361 Final 1
Why does a force directed through an axis of rotation not cause rotation at the axis?
there is no lever arm available which has the force have nothing to act on which causes the torque to not be produced which mean there will be no moment produced
biceps at the elbow lever
third class
in the human body, most lever systems are
third class
medial deltoid at the shoulder lever
third class
patellar tendon at the knee lever
third class
tweezers, arm, baseball bats, hockey sticks, golf clubs, fishing, unattached oar, someone sweeping, stapler, tongs
third class lever
most levers within the body are
third class levers
How many principle axes are there for the human body?
three
principal axes
three mutually perpendicular axes passing through the total body center of gravity
Electromechanical Delay
time of muscle activation and force recorded (useful for reflex studies)
Why are golf club heads weighted?
to increase the moment of inertia of the club head rotating around the shaft
Why do skilled high jumpers lower their COM on the last step?
to increase time of support between foot and ground to increase vertical velocity at take-off to increase impulse at take-off
how are resistance training devices designed?
to match resistance generated by the torque of the muscle. isokinetic exercise is constant angular velocity at a joint when applied to exercise machinery
Why does a figure skater cross his arms tightly across the chest when performing a quadruple axel?
to reduce moment of inertia and to increase angular velocity
How does density of bones influence injury risk?
Denser bones decrease injury risk.
when are local and remote terms used?
to sum the angular momenta of all the body segments about a principal axis to get the total-body angular momentum about that axis ex: doing a somersault, have to sum angular momentum of one segment such as the lower leg
The higher the position of the CG, the ______ the potentially disruptive torque created if the body undergoes an angular displacement.
top heavy
The product of muscle tension and muscle moment arm produces a
torque at the joint crossed by the muscle
When the resultant joint torque and angular velocity curves are on the same side of a running graph ______
torque is concentric
principal moment of inertia
total-body moment of inertia relative to one of the principal axes
transfer of angular momentum
transferring angular velocity at least partially from one principal axis of rotation to another
What is the main plane and axis of motion when punting a football?
transverse axis, sagittal plane
A motionless body is in a state of static equilibrium.
true
If force is applied directly to the axis of rotation, torque will equal zero.
true
Is the following sentence true or false? A compound machine is a combination of two or more simple machines that operate together.
true
Is the following sentence true or false? The ideal mechanical advantage of an inclined plane is the distance along the incline plane divided by its change in height.
true
T or F? All second-class levers have a mechanical advantage greater than one because the input arm is longer than the output arm
true
When other factors remain constant, an increase in the mass of an object will subsequently increase the object's stability.
true
third class lever example
tweezers, bicep curl, human arms and legs, shovels, fishing rods, tongs
the force of muscular tension is resolved into _______
two force components. rotary component and parallel component
when does the amount of angular momentum change?
when an external torque does act
eccentric torque
when muscle torque & joint movement occur in opposite directions
concentric torque
when muscle torque & joint movement occur in same direction
when is it easiest to initiate rotation?
when the force is applied perpendicularly and far away as possible from the AOR
when is angular momentum conserved?
whenever gravity is the only acting external force remains constant in the absence of external torques
what characteristics distinguish levers as 1st class, 2nd class, or 3rd class?
where the fulcrum, input arm, and output arm is are located
Which of the following can increase base of support?
widen stance add more points of contact (i.e. 3-point stance to 4-point stance)
Likewise, radius of gyration for a body segment such as the forearm is greater with respect to the
wrist than with respect to the elbow.
can two joint muscles be concentric at one joint and eccentric at a second joint?
yes
do the magnitude of a force and the length of its moment arm equally affect the amount of torque generated?
yes
The feeling you get when rounding a corner in a car and
you're being pushed in the direction of the outside of the curve.
Form Drag
Depends on objects's size and shape. Drag force acting on an object within fluid caused by difference in pressure on two sides of the object. More pressure in the front of the person than in the back
Surface Drag
Depends on the surface material. Drag force acting on an object within fluid caused by the friction between the surface of object and the fluid. Causes a negative force.
Why is this advantageous for an off-center hit?
Designed to increase the club head inertia reduces the tendency of the club to rotate about the shaft during an off-center hit.
Effort Arm
Distance between the force and the axis. Effort arm generates force to work against resistance arm. Effort arm refers to muscle attachment point.
Resistance Arm
Distance between the resistance force and the axis
what is the antagonist and what does it control?
The tension is the antagonist controls the velocity of the movement and enhances the stability of the joint
Torque
The turning effect of an eccentric force Equals the product of the force magnitude and the length of the moment (torque/effort/force) arm - there are two types, torque arm, resistance arm -
a simple machine that consists of two disks or cylinders, each with a different radius that rotate around each other
wheel and axle
second class lever example
wheelbarrow, nutcracker, calf raise, staplers, bottle openers, nail clippers
transfer of angular momentum example
when a diver changes from a primarily somersaulting rotation to one that is primarily twisting
What is radius of gyration and does it change based on the axis of rotation? Explain
Distance from the axis of rotation to a point where the body's mass would be concentrated without altering its rotational characteristics Yes, when the radius of gyration is shorter more mass is concentrated closer to the axis of rotation, the moment of inertia is less, and the object is easier to swing.
Center of Mass
Distribution of mass is equal in all directions. Calculating center of mass requires knowing how mass is distributed throughout the body. Center of mass is fixed on a projectile motion path, even if other body parts alter position . Center of mass change change locations but still follow projectile motion.
Which factor will have the greatest influence and why?
Distribution of mass with respect to the axis of rotation because angular momentum is proportional to the square of the radius of gyration.
how to calculate the IMA of a wheel and axle.
Divide the diameter where input force is exerted by the diameter where output force is exerted.
Drafting
Drafting at higher velocities will have more impact than at lower velocities because at higher velocities drag force is more meaningful. When traveling behind someone both air pressure/density and relative velocities are decreased allowing the person to use less energy to overcome drag force.
how does takeoff from a springboard related to angular momentum?
During takeoff, a diver must attain sufficient linear momentum to reach the necessary height and sufficient angular momentum to perform the required number of rotation. If multiple-rotations is required, the angular momentum generated at takeoff increases as rotational requirements of the dive increase.
Third class levers
Force lies between the axis (fulcrum) and the resistance A-F-R - Designed to favor speed and range of motion - * Third class are a common place in the body - Examples: fishing, baseball, field hockey, sports, rowing, diving - real life example: a good example is the action of the bicep as it lifts a load in the hand while pivoting at the elbow -
Three parts of a lever
Force point (F): point where effort is applied, the insertion point of the muscle Resistance point (R): point where resistance acts, ie the weight, perpendicular from the fulcrum Fulcrum (A): axis of motion, center of gravity on the body segment
Drag Force
Force that acts in opposition to the relative motion of an object with respect to fluid
Effort Force
Force that makes the lever move. (input force)
Calculating torque
Force x force arm (F x FA) If F x FA = R x RA, the lever is in equilibrium - R x RA > F x FA - resistance force produces movement - F x FA > R x RA - force produces movement -
Angular Kinetics
Forces that cause angular motion
Power Spectrum Graph
Frequencies of power spectrum graph provide information on fatigue and determining active muscle type. Allows for calculation of median frequency (where 50% of total power is observed).
How is angular momentum primarily derived during aerial skills?
From the angular impulse creased by the reaction force of the support surface during takeoff.
Somersaulting occurs around which of the following axes of rotation?
Frontal
Where is radius of gyration located in relation to center of gravity (COG)?
Further from the axis
How does body mass influence injury risk?
Greater body mass puts greater force on bones, which can increase injury risk. Greater body mass also relates to denser bones, which can decrease injury risk.
equilibrium
If either the force (F) or the force arm (FA) change, a turning effect will occur in the direction of the increased torque.
Which of the following is true of a baserunner weighing 70 Newtons and a baserunner weighing 50 Newtons?
If the baserunners run at the same velocity around the bases, the heavier baserunner will have to lean in more towards the pitchers mound due to a greater centripetal force
First class lever
In the first class lever the axis point is in the middle and the resistance and force points are on the edges. Ex. Tricep muscle at the elbow/ "see-saw"
If a diver goes from a full layout position to a tuck position, what will happen to her angular velocity?
Increase
How to increase stability?
Increase base of support
Centrifugal force is misnomer. What is really happening when you feel a pull to the outside while rounding curve?
Inertia
Angular Inertia
Moment of Inertia: object's resistance to rotation. Units: kgm^2. The larger amount of angular inertia means that a large torque is needed to bring about the same angular velocity in same amount of time. An object can have different angular inertia about different axes.
explain moment of inertia and its formula:
Moment of inertia: inertial property for rotating bodies representing resistance to angular acceleration; based on both mass and the distance the mass is distributed from the axis of rotation I = mr^2 ii. A body's inertia is directly proportional to...its mass iii. Resistance to angular acceleration is a function of what two factors?
Mechanical Device
Motion at a joint which occurs as a result of muscle tension exerting force on a bone exemplifies a simple mechanical device.
With levers in the human body, forces rarely act at perfect right angles.
Muscle forces that exert torque are dependent on point of insertion of the muscle; & length, tension, and angle of pull changes -
what factors affect the capability for a muscle to generate force? (6)
Muscle length Cross-sectional area Moment arm Angle of attachment
Why is a bat easier to swing if you grip the barrel instead of the handle?
Radius of gyration
Mechanical Advantage
Ratio between the effort arm and resistance arm. In the body most situations lead to a mechanical advantage of less than 1 (leads to more range of motion and speed rather than strength)
Fiber Arrangement
Series: fibers arranged end to end along the long axis of a muscle. Series arrangement produces less strength but more range of motion and speed. (Fusiform)
How does positioning of fulcrum with respect to tip of the board affect performance of a backward somersault?
Setting the fulcrum further back from the tip of the board results in greater downward board tip vertical velocity at the beginning of takeoff.
What does a raw EMG signal show?
Show the sum of all voltages being received from any motor units the electrode is in position to read. Since the signals are being summed, some signals will amplify others while some will diminish others.
When a discus thrower spins and then releases the discus, what direction will it travel?
Tangent to the circular path at release
Which of the following is the most important factor affecting the magnitude of centripetal force?
Tangential linear velocity
What is the benefit for limbs being tapered?
Tapered limbs means that more mass is distributed toward the proximal end. This means more mass toward the center of the body, which makes moment of inertia less and makes rotation easier. It takes less effort to move and we are able to rotate limbs with less resistance. This decreases metabolic cost.
How much force can a tendon handle?
Tendon can handle greatest amount of tensile stress than compression and shear.
What is centrifugal force? Is it real?
The absence of centripetal force acting on an object no.
how is diving related to conservation of angular momentum?
The amount of angular momentum present at the instant of takeoff remains constant through out the dive. As diver goes from an extended layout position into a tuck, the radius of gyration is decreased, thus reducing the body's principal moment of inertia about the transverse axis. Tighter the tuck , the greater the angular velocity. Once somersault is completed, diver extends fully, thereby increasing total body moment of inertia with respect to the axis of rotation.
Fulcrum (A)
The axis or fixed point about which the lever rotates -
Third Class Lever
The effort arm is between the fulcrum and the resistance arm. Example: bicep curl (elbow joint is the fulcrum, effort arm comes from forearm muscle, resistance is the weight held in hand)
what kind of lever is the elbow acting as when we do a bicep curl?
The elbow flexors contract eccentrically to apply a braking resistance and to control movement speed during the down phase of a curl exercise. Second class lever
First Class Lever
The fulcrum is between the effort arm and resistance arm. Example: tricep extension, moving hear backward and forward.
Types of levers
The human musculoskeletal system is made up of levers with Short Force Arms and Long resistance Arms Humans are built for speed and range of movement at the expense of force production -
What happens to a golf ball when initial velocity is increased early in the flight?
There will be a greater upward acceleration and then more slowing of the ball.
What do shin guards do?
They distribute the force over a larger area, which decreases the stress. Cushioning allows force to be spread out over a longer period of time, this causes a smaller peak force during contact and less pressure to the area.
Why do smaller gymnasts have an advantage over larger, stronger gymnasts in performing skills involving whole-body rotations?
They have smaller moments of inertia
center of gravity/center of mass
The point around which the mass and weight of a body are balanced in all directions The CG of a symmetrical object of homogeneous density is the exact center of the object point about which the sum of torques produced by the weights of the body segements are equal to zero
Third class lever
The second class lever has the force in the middle and the resistance and axis on the edges. Ex. bicep muscle/ "shovel"
Second class lever
The second class lever has the resistance point is in the middle and the force and axis points are on the edges. Ex. "wheel barrow"
impulse-momentum relationship equation
Tt= delta H Tt= (Iw)2 - (Iw)1 T= torque t= time H= angular momentum I= moment of inertia w= angular velocity 1,2 subscripts= initial and second or final points in time
What does the principle of conservation of momentum for angular motion mean? Explain it without the author's words
Without external forces, the total angular momentum of a system stays the same
Why is a bat easier to swing if you grip the barrel instead of the handle?
k is reduced
What are the appropriate units fro angular momentum?
kg(m2/s)
Which of the following are accurate units for moment of inertia?
kg(m^2)
Which of the following are accurate units for moment of inertia?
kg•m2
What are the appropriate units for angular momentum?
kg•m2/s
The radius of gyration of the forearm for flexion/extension movements is much ___than for pronation/supination
larger
When the body assumes a tucked position during a somersault, its principal moment of inertia (and resistance to angular motion) about the transverse axis is ___ than when a body is in anatomical position
less
mechanical advantage of 1st class levers
less than 1, greater than 1, or equal to 1. moment arm of resistance and force can vary
When muscles develop tension, pulling on bones to support or move the resistance created by the weight of the body segment(s) and possibly the weight of an added load, the muscle and bone are functioning mechanically as a____
lever
a screwdriver used to pry the lid off a paint can is an example of a__________
lever
what do you use to pry/ lift things?
lever
what is a rigid bar that is free to move around a fixed point (fulcrum)
lever
first class lever actions of agonist and antagonist muscle groups
lever positioned with the applied force and the resistance on opposite sides of the axis of rotation Actions of agonist and antagonist muscle groups on opposite sides of a joint axis
first class lever
lever positioned with the applied force and the resistance on opposite sides of the axis of rotation resistance and force on opposite sides of fulcrum (load=resistance, effort=force)
third class lever definition
lever positioned with the applied force between the fulcrum and resistance
second class lever definition
lever positioned with the resistance between the applied force and the fulcrum
list the 6 types of simple machines
lever, wedge, wheel and axle, inclined plane, screw, pulley
Torque is the angular equivalent of
linear force
Torque is the angular equivalent of what?
linear force
During a takeoff from a springboard or platform, a competitive diver must attain sufficient ____ and sufficient ___ to perform the required number of rotations
linear momentum to reach the necessary height (and safe distance from board or platform) -angular momentum -
Rotating around which of the following principal axes of rotation has the least moment of inertia (anatomical position)?
longitudinal
What is the main plane and axis of motion of a spin in skating?
longitudinal axis, transverse plane
moment of inertia formula for a single particle - I= mr^2
m - particle's mass r - particle's radius of rotation
Which of the following variables contribute to moment of inertia?
m and k
where is the moment arm within the human body?
With in the human body, the moment arm for a muscle with respect to the joint center is the perpendicular distance between the muscle's line of action and the joint center.
If a pendulum stops swinging, which of the following is/are true?
angular velocity = 0 and angular momentum = 0
What is the main plane and axis of motion of a cartwheel?
anterior-posterior axis, frontal plane
Which of the following is/are true regarding dynamic equilibrium?
applies to bodies in motion and first identified by D 'Alembert
Radians
arc length divided radius
All classes of lever
are used to make a load easier; all have a fulcrum, input force, and output force; and all have a IMA found by diving the input force by output force.
angular momentum and mass or angular velocity
as mass or angular velocity increases, angular momentum increases
Which of the following is/are true regarding a force couple?
created by equal forces on opposite sides of an axis and created by forces acting in the same angular direction
Which of the following does not increase stability?
decrease mass
When knee flexion is increased, what happens to the moment of inertia of the leg about the hip?
decreased
resistance to angular acceleration factors
depends on amount of mass of an object distribution of that mass with respect to axis of rotation
A concept indicating a balance between applied forces and inertial forces for a body in motion is called ________________.
dynamic equilibrium
How come gravity does not affect angular momentum?
d⊥ = 0 and T = 0
The more closely concentrated the mass is to the axis of rotation of an implement, the ___ it is to swing
easier
Intrinsic Factors
factors that are directly related to person participating in activity: skeletal (density, structure, size, shape, architecture), muscular (structural composition, size, strength, endurance, flexibility), tendon (locations of origins and insertions, yield and ultimate strength), neuromuscular (timing of muscle activation), body (mass, height, anthropometrics)
Ultimate Strength
failure: complete rupture or break will occur
Running barefoot results in higher joint torque at the knee than using running shoes.
false
The center of gravity of an object is always located within the object.
false
T or F? First class levers always have a mechanical advantage that is greater than
false; it can be greater than 1, equal to 1, or less than 1
Parallel:
fibers arranged parallel to each other. Parallel arrangement produces more strength but less range of motion and speed. (Unipennate, bipennate)
newtons third law angular
for every torque exerted by one body on another, there is an equal and opposite torque exerted by the second body on the first ex: doing sit ups, the feet tend to rise upwards and produce a torque equal and opposite to torque produced by body rising upwards
Torque is the angular analogue of what?
force
3rd class lever
force (F) between axis (A) & resistance (R) - a-f-r -
centripetal force
force directed toward the center of rotation for a body in rotational motion prevents a rotating body from leaving its circular path while rotation occurs around a fixed axis direction of centripetal force is always towards center of rotation
what is Centripetal Force?
force directed toward the center of rotation for a body in rotational motion. It prevents the rotating body from leaving its circular path while rotation occurs around a fixed axis. It produces the radial component of the acceleration of a body travelling on a curved path.
what conditions must be met for a body to be in a state of static equilibrium (3)
1. The sum of all vertical forces (or force components) acting on the body must be 0, 2. The sum of all horizontal forces (or force components) acting on the body must be 0, 3. The sum of all torques must be zero.
factors that affect magnitude of body's angular momentum
1. its mass (m) 2. distribution of that mass with respect to the axis of rotation (k)
what makes angular momentum change?
1. magnitude and direction of external torques 2. length of time interval over which each torque acts such as angular impulse and linear impulse 3. motion of body segments
Density of air
1.2 kg/m^3 around sea level, .7 kg/m^3 at high elevations
Density of water
1000 kg/m^3
Angular Inertia
An objects resistance to angular motion, Units=kgm^2
third class lever
force is closer to the axis of rotation/fulcrum, where the resistance is on the outside/further away (load=resistance, effort=force)
parallel component
force is directed parallel to the bone pulls bone away from joint center (dislocating component) pulls bone toward joint center (stabilizing component)
Muscle strength
force production of a muscle
Pressure
force/area (externally)--load creating the stress
Stress
force/area (internally)--load on tissues. 1 pascal=1 Newton applied over 1m^2
Somersaulting occurs around which of the following axes of rotation?
frontal
3 principal axes
frontal anteroposterior longitudinal each of which passes through the total body CG
the fixed point that a lever rotates around is called the____________
fulcrum
because most lever systems are third class in the human body, this arrangement promotes
range of motion and angular speed of joints
Recruitment Patterns
rate at which motor units are recruited -
Centrifugal force is a misnomer. What is really happening when you feel a pull to the outside while rounding a curve?
iinertia
Which of the following is/are true regarding center of mass?
in a spherical ball with evenly distributed mass, it is in the exact center it is the point around which a body's weight is equally balanced regardless of body position it may be located outside an object or body
A slanted surface along which a force moves an object to a different elevation is called a(n) ______________
inclined plane
If a diver goes from a full layout position to a tuck position, what will happen to her angular velocity?
increase
Which of the following will improve leverage?
increase force arm and decrease resistance arm
as muscle force increases, resistance
increases
moment of inertia
inertial property for rotating bodies representing resistance to angular acceleration based on both mass and the distance the mass is distributed from the axis of rotation
why are smaller gymnasts able to perfrom whole body rotations?
As we grow segments of moment of inertia affect resistance to angular rotation. thats why smaller moments of inertia means smaller gymnasts have an advantage in performing whole body rotations, despite the fact that larger gymnasts may have greater strength and generate more power.
What happens to drag force at high elevations?
At high elevations there is a lower density and lower air pressure. This decreases the drag force. There is less air resistance but it is also more difficult to get oxygen into the blood stream.
First class levers
Axis (Fulcrum) lies between the force and the resistance F-A-R - Produces balanced movements when the axis is midway between the force and the resistance - When the axis is close to the force lever produces speed and range of motion - When the axis is close to the resistance, lever produces force - Examples: - Scissors, See-Saw, rowing - First class levers the best example in the body is found with the skull pivoting on the atlas vertebrae of the spine with the weight of the head held by the trapezius and the sternocloeidmastoid muscles of the neck. -
what is Moment of inertia?
inertial property for rotating bodies representing resistance to angular acceleration. Based on both mass and the distance the mass is distributed from the axis of rotation.
the distance between the fulcrum in a lever and the input force
input arm
the force exerted ON a machine
input force
A-F-R (third lever)
is shorter force arm and longer resistance arm -
Young's Modulus
Ratio of stress to strain (stress/strain). Describes the compliance or stiffness of a biological structure (calculates the properties of tissues). Determines how much force is require to deform a structure. It is the slope of the stress-strain curve up to the yield point (between the elastic and plastic region). A steep slope means the structure is more stiff, a gradual slop means the structure is more compliant. (measured in pascals)
Why do spring coaches stress "heel to buttocks" during sprints?
Reduces moment of inertia of the leg with respect to the hip
What effect does "choking up" on a bat have?
Reduces moment of inertia, and increases angular velocity of swing
Which of the following is/are most important factor(s) affecting the magnitude of centripetal force?
tangential linear velocity
Factors that affect muscle force
Cross sectional area, fiber arrangement, fiber length, contraction velocity, fiber type, neural factors
How does air density affect lift and drag force?
Decrease in density decreases lift and drag force (higher elevations). Increase in density increases lift and drag force (lower elevations).
When knee flexion is increased, what happens to the moment of inertia of the leg about the hip?
Decreased
Contraction Velocity
Relationship between muscle action type, velocity and force production. Concentric (shortened) muscles have decreased force when velocity is increases. Eccentric (lengthened) muscles have increased force when velocity increases.
Which statement(s) is/are true regarding postural sway?
it affects balance in the elderly it is reduced by widening the BOS to a certain pointit is increased by putting one foot in front of the other
Which of the following is a characteristic of torque?
it is a vector quantity, it is characterized by magnitude, it is characterized by direction
a fulcrum is related to a lever because....
it is the point at which the lever moves around; it helps the lever lift things; depending on where you place it, there are different levers than can be made
What will happen to the COM of a human body if the arms are raised up overhead?
it will move up
what is the force acting at the joint?
joint reaction force
Which of the following factors influences the amount of torque produced by muscles at a joint?
the amounts of tension generated by the muscles and the arrangement of the muscles around the joint
where is the angle of maximum mechanical advantage on a joint?
the angle where the most rotary force can be produced
For a multisegmented object such as the human body, angular momentum about an axis is the sum of.
the angular momenta of the individual body segments.
The closer the horizontal location of the CG is to the boundary of the base of support, the ______ is the force required to push it outside
the base of support, thereby disrupting equilibrium.
In analyzing the human body as a projectile, which of the following quantities follows a parabolic path?
the center of mass
because most lever systems are third class in the body, what does this mean about the force generated/resistance force?
the forces generated must be in excess in the resistance force to provide movement/positive mechanical work since the mechanical advantage is less than 1
in a 1st class lever
the fulcrum is between the input force and output force, IMA can be less than one, greater than one, or = to 1
Which of the following variables contribute to moment of inertia?
M and k
Centripetal force is related to which of the following?
radial acceleration
Which of the following will benefit mobility?
raise center of gravity
mechanical advantage of 2nd class levers
(load=resistance, effort=force) always greater than 1. the resistance is closer to the fulcrum than the force, so the resistance moment arm=always less than the force moment arm mechanical advantage=moment of force/moment of resistance, ration always greater than 1
mechanical advantage of 3rd class levers
(load=resistance, effort=force)always less than 1. the force is closer to the fulcrum than the resistance, so the force moment arm=always less than the resistance moment arm. mechanical advantage=moment of force/moment of resistance, ration always less than 1
Rotation
A force offset from center of mass causes rotation
In the human body, angular momentum about a given axis of rotation is the sum of the angular momentum of the body segments. They include two components:
1. Local term: based on the segments angular momentum about its own segmental CG. 2. Remote term: represents the segments angular momentum about the total body center of gravity. 3 factors affecting the magnitude of a body's angular momentum: - 1. Its mass (m) 2. Distribution of mass with respect to the axis of rotation (k) 3. Angular velocity of the body (w) -
what are the linear kinetic quantities?
1. Mass (m) 2. Force (F) 3. Momentum (M) 4. Impulse (ft)
what are the angular kinetic quantities?
1. Moment of inertia (I) 2. torque (T) 3. Angular momentum (H) 4. Angular impulse (Tt)
Steps of muscle activation electrical potential around muscle membrane
1. Motor unit stimulate 2. Acetylcholine released into sarcomere 3. Positive sodium ions flow into negatively charged intracellular space 4. Positively charged calcium ions released 5. Calcium and ATP make muscle contract at actin and myosin level At -55 action potential/muscle activation occurs -
The amount of torque which must by generated by the biceps brachii at the elbow in order to maintain the arm in a particular position is 50 Nm. If the biceps attaches to the radius at a perpendicular distance of 3 cm from the joint center at the elbow, how much force must the muscle produce?
1667 N
which direction will the teeter totter go?
190 (1.6)=304 200 (1.5)=-300 304-300=+4Nm towards the girl because it is moving in the counter clockwise direction (see notes, slide 6)
A claw-tooth hammer being used to pry up a nail is an example of which class of lever?
1st class
A seesaw is an example of which class of lever?
1st class
Which one of newton's laws (angular) forms the underlying basis for the principle of conservation of angular momentum?
1st law
Describe Newton's three laws as they apply to angular kinetics.
2) The greater the bodies mass the greater its resistance to linear acceleration; therefore miss is a body's inertial characteristic for considerations relative to linear motion.
A lever positioned with the applied resistance between the axis and the force is a ________ class lever.
2nd class
A wheelbarrow is an example of which class of lever?
2nd class
Types of Levers
3 types, Each is classified by the relative position of the fulcrum(axis), the resistance and the force
Newton's first law, angular
A rotating body will maintain a state of constant rotational motion unless acted on by an external torque
what is Newtons First Law in angular movement?
A rotating body will maintain a state of constant rotational motion unless acted on by an external torque.
In the human body, most of the lever systems formed by muscles pulling on bones are what class?
3rd class
The resistance arm (RA) will always be longer than the force arm (FA) in what class lever?
3rd class
Which of Newton's laws (angular analogues) explains why a batter wears cleats?
3rd law - reaction
Lever
A lever is a simple mechanical device used to produce turning about an axis resulting in a mechanical advantage for SPEED and FORCE.
Why is a light weight shoe more beneficial?
A light weight show is more beneficial because having less mass at the end of the limb will decrease the angular inertia causing less resistance. A light weight shoe with some cushioning (protection) is an appropriate choice in footwear for performance.
Understanding a bicep curl (arm holding a weight)
A muscle must create opposite torque to hold this position. As the elbow extends, the angle between the line of force of muscle force and the forearm decreases. This brings the perpendicular distance from the line of muscle closer to the elbow joint, decreasing the effort arm that the muscle produces. As the moment arm decreases, the force required to generate torque increases. You need more force when the effort arm is shorter.
what is Newtons Second Law in angular movement?
A net torque produces angular acceleration of a body that is directly proportional to the magnitude of the torque, in the same direction as the torque, and inversely proportional to the body's moment of inertia.
Newton's 2nd law, angular
A net torque produces angular acceleration of a body that's directly proportional to the magnitude of the torque, in the same direction as the torque, and inversely proportional to the body's moment of inertia.
what contributes to net joint torques
A number of factors, including weight of body segment, motion of body segments, and action of external forces, may contribute
Tangential Acceleration
Acceleration in the direction of motion, it is tangent to the circular path of a point of a rotating object. It is perpendicular to the radius. With constant angular acceleration, tangential acceleration increases as radius increases.
Centripetal Acceleration
Acceleration toward axis of rotation
Lift Force
Acts perpendicular to the motion of an object through a fluid. Lift force can be in any direction.
What are the advantages and disadvantages of setting the fulcrum further away from the tip?
Adv: allows diver more time in contact with board to generate angular momentum and increased vertical velocity going into the dive Disadv: requirement of increased hurdle flight duration and the necessity of reversing downward motion from a position of greater flexion at the knees.
Eccentric Axis
An axis of rotation that does not go through the objects center of gravity.
Which of the following acts to produce a change in angular momentum?
Angular impulse
Which of the following is referred to as the "quantity of angular motion" possessed by a body?
Angular momentum
Is angular momentum conserved for a gymnastic vault while in the air?
Angular momentum is conserved in a gymnastic vault in the air. Gravity is the only force pulling through their center of rotation. This means that no other torques are acting on the gymnast and therefore there is no change in angular momentum.
Is angular momentum conserved in a spin about the longitudinal axis of an ice skater?
Angular momentum is conserved while the skater is in the air. Gravity is acting through the axis of rotation so there is no change in angular momentum while the skater is in the air but when on the ground torque is created as angular momentum is taken away. Once the skater leaves the ice, there is an inverse relationship between angular velocity and moment of inertia. The mass doesn't change so the change in angular inertia throughout the flight depends on change in body position (mass distribution). As the skater pulls their arms closer to center, inertia gets smaller so velocity gets bigger. As they extend their arms out, inertia increases again and slows the rotation.
Is angular momentum conserved for a giant swing in gymnastics?
Angular momentum is not conserved for a giant swing in gymnastics because the axis of rotation is not in the same location as the center of mass, the rotation is around the bar. Therefore gravity creates a torque on the way down, which increases the angular momentum. Then momentum is taken away on the way up.
In the absence of external torque, which of the following will increase when moment of inertia decreases?
Angular velocity
Which of the following quantities increases as moment of inertia decreases during the airborne phase of a dive?
Angular velocity
If a pendulum stops swinging, which of the following is/are true?
Angular velocity/momentum = 0
Cross Sectional Area
Area perpendicular to long axis/pull of muscle force. Aka Muscle thickness. It is proportional to muscle's ability to produce active force. Hypertrophy (growth of muscle fiber size), hyperplasia (proliferation of muscle cells, less common)
Describe the moment of inertia in running
As leg rotates, it rotates around the hip joint center at the end of the leg. When extended, that mass of the leg is located far away from the axis of rotation. This distribution creates a large moment of inertia. When the knee flexes, the mass is located closer to the hip joint center, which creates a smaller moment of inertia about the axis of rotation. During the swing phase of running, flexion should be optimized.
In overhead throwing sports, describe the concept of a "kinetic chain". Provide examples
As the arm moves forcefully forward, angular momentum is progressively transferred from proximal to distal segments. Throw: motions of elbow extension and wrist flexion accelerated by motion of the trunk and upper arm, as angular momentum is transferred from segment to segment. -Tennis serve: angular momentum produced by movements of trunk, arm, and legs, with a transfer of momentum from the extending lower extremity and rotating trunk to the racket arm, and finally to the racket.
How much force is acting on the skydiver?
BW = 580 N - a = -8.8m/s2 59.7 N
Coefficient of Drag
Based on the surface material and shape of an object.
Fiber Length
Basis of force production is the attachment of myosin cross bridges to actin filaments. Optimal overlap (sarcomere resting length) of myosin and actin leads to optimal force production. Greatest number of actin an myosin overlapping means greatest force production.
Headwind
Blowing opposite to the object's motion (makes it more difficult to move forward)
Tailwind
Blowing with the object's motion (coming from behind, which makes it easier to move forward)
Frontal Plane
Body cut into anterior and posterior halves
Sagittal Plane
Body cut into right and left halves
Transverse Plane
Body cut into superior and inferior halves
Which can structure can handle the greatest amount of stress? (tendon, ligament, bone)
Bone (can handle greatest amount of stress)Then tendon - Then ligament -
How do you minimize form drag?
By reducing frontal area
How would a cyclist decrease their coefficient of drag
By tucking and leaning forward. Their shape will become more stream line and decrease their frontal area, which will ultimately increase their velocity.
How can electrical potential be measured?
By using surface electrodes
How much force can cortical bone handle?
Can handle most amount of compression (100-280 degrees) then tension (90-170) - then shear (50-100) -
What effect can growth have on a gymnast's performance?
Can result in declines in their performance capabilities due to changes in body proportions with growth.
Stability
Capacity of an object to return to equilibrium (or capacity of an object to maintain equilibrium)
Bernouli's Principle
Causes lift force. Pressure is lower on the side with faster moving fluid. Pressure is higher on side with slower moving fluid. Faster moving fluids exert less pressure laterally than slower moving fluids. Examples: wings on a plane, rudders on a boat
Which of the following is known as "center-seeking" force?
Centripetal force
What is angular impulse?
Change in angular momentum equal to the product of torque and time interval over which the torque acts a. Significant changes in an object's angular momentum may result from The action of a large torque over a small time interval or from the action of a small torque over a large time interval
What is angular impulse?
Change in angular momentum equal to the product of torque and time interval over which the torque acts.
What influences angular momentum?
Change in angular velocity, change in direction of axis of rotation, change in moment of inertia (ie change in mass or mass distribution), or combination of all three.
what impacts two measures of standing balance and what are those two measures?
Changes in foot position have been found to affect two measures of standing balance: The location of the line of gravity and postural sway.
What does choking up on a bat do?
Choking up on a bat reduces the radius of the bat. This brings the distribution of mass closer to the body which decreases the moment of inertia, therefore it takes less effort to rotate the bat. Although, when the radius is reduced the linear velocity of the bat decreases.
If total body angular momentum is 0, what will happen as the result of a forceful movement such as a spike?
Compensatory rotation in lower body in opposite direction
Eccentric force
Eccentric force - force applied in a direction not in line with the center of rotation of an object with a fixed axis For rotation to occur an eccentric force must be applied - example: throwing a ball, lifting a platform, pulling equally against someone. -
Limitations of Electromyography
Electrodes are separated from motor units by skin, tissue, and other muscles.
Centrifugal Force
Equal and opposite force to centripetal force. Centrifugal acceleration away from axis of rotation
lengths of arms
F-A-R(first lever) is equal resistance arm and equal force arm
centripetal force equation angular
Fc= mrw^2 Fc= centripetal force m= mass r= radius of rotation w= velocity- speed of rotation (most influential bc force is proportional to square of angular velocity
explain cat rotation
First phase consists of internally generated rotation of segment 1 around its longitudinal axis with a compensatory rotation of segment 2 in opposite direction around longitudinal axis of segment 1. Second phase consists of rotation of segment 2 around its longitudinal axis in the same direction originally taken by segment 1 with a compensatory rotation of segment 1 in the opposite direction around axis 2. Resulting rotation of both phases has small angular velocity because k is relatively large with respect to axis -
Full Wave Rectification
First step in processing information. Taking absolute values of all data points. Then data is usually filtered to remove noise.
Why is it recommended to flex your knees and hips when lifting a heavy object rather than using your hips and back?
Flexing knees and hips reduces that resistance arm and torque of the lumbar spine. This gives you more strength.
Newton's 3rd Law applied to Angular Motion
For every torque applied to one body there is an equal and opposite torque applied on the second body by the first. It can be applied to one body with multiple segments rotating around an axis.
what is Newtons Third Law in angular movement?
For every torque exerted by one body on another, there is an equal and opposite torque exerted by the second body on the first.
newton's third law, angular
For every torque exerted by one body on another, there's an equal and opposite torque exerted by the second body on the first.
Toque is the angular analogue of what?
Force
Principle of Levers
Force X Force arm = Resistance X Resistance arm Torque = force x force arm / resistance x resistance Mechanical Advantages of Levers - MA = FA/RA the efficiency with which a lever is able to magnify a force
Resistance (R)
Force acting on the lever resisting the force may also be referred to as Resistance Force (RF) or Load -
Force (F)
Force applied at some point along the lever in order to overcome a resistance may also be referred to as Effort (E) or Effort Force (EF)
Explain centripetal force and provide a real-life example.
Force directed toward the center of rotation for a body in rotational motion. AKA center-seeking force. Swinging a ball on the end of a string in a circle.
What is centripetal force(F)?
Force directed toward the center of rotation for the body in rotational motion
What is the purpose of a golf swing?
General terms: to hit the ball as far as possible in the right direction Mechanical terms: to maximize club head velocity while optimizing fluid dynamics and direction - Wolfe's Law - Tissue adapts to level of stress placed on it, level of adaptation depends on typical loading. If load is too high and/or too frequent it could lead to injury rather than adaptation. This law applies to any tissue that receives blood flow.
What is the purpose of a vertical jump test in mechanical terms?
General terms: to jump as high as possible Mechanical Terms to maximize vertical take off velocity - Characteristics: swing arms up during take off phase - Influence: due to newton's 3rd law, swinging arms upwards pushes body down. More force goes into the ground, which means more force will push body back up. It also raises center of mass so they begin jumping from higher. -
When performing a double or triple, where is the angular momentum generated and where is it contributed from? Why is tight positioning of the arms and legs so important?
Generated by skater's movements and changes in total body moment of inertia prior to takeoff. Contributed by motion of the free leg that's extended to increase total-body moment of inertia around skater's vertical axis. Tight positioning of arms and legs is essential for maximizing revolutions while airborne because it decreases the moment of inertia.
Which lever classes do a golf club, a swinging door, and a shovel belongs to?
Golf club: third class lever where the top hand is the axis, the bottom hand is the force, and the bottom of the club is the resistance Swinging door second class where the hinges are the axis, the resistance is the door, and the handle is the force Shovel third class, see golf club
Which of the following is/are accurate formula(s) for angular momentum?
H = Iω and H = mk2ω
angular momentum equation
H= Iw
H=mk^2w
H= angular momentum I= moment of inertia w= angular velocity k= distribution of mass w respect to the axis of rotation
Which of the following is/are accurate formula(s) for angular momentum?
H=Iw, or H=mk2w
Angular Momentum
H=angular velocity*moment of inertia. Angular momentum is conserved when no external forces are acting on object. If axis of rotation is in the same location as center of mass, gravity will not cause torque and will not affect angular momentum.
What affect does humidity have on air density.
Higher humidity means lower density. Lower humidity means higher density. (this is because water vapor has lower density than air). Humidity has least impact on density.
What affect does temperature have on air density?
Higher temperature means lower density (because of faster moving molecules means fewer molecules fit). Lower temperatures means higher density.
What are differing body motions of highly skilled divers and lower skilled divers? How does this affect performance?
Highly: perform arm swing with arms fully extended. Maximizes moment of inertia of arm and angular momentum generated. Increases performance. Lower: often must use flexion at elbow to reduce moment of inertia of arm about shoulder so arm swing can be completed during time available. Decreases performance.
Radius of gyration
How mass is distributed. Mass closer to center has smaller radius of gyration, which means the object is easier to rotate. When mass is distributed farther from the center there is a larger radius of gyration, the object has larger moment of inertia, which means it is more difficult to rotate. Radius of gyration is the root mean square distance of each point on an object relative to the center of mass.
Important points to remember:
Human movement occurs through the use of a system of levers. The Anatomical levers of the human body cannot be changed Levers can more efficiently maximize efforts (force production) of the body
What is the formula for moment of inertia with respect to an axis? Explain the formula
I = mk^2; m = total body mass, k = radius of gyration, I = moment of inertia with respect to an axis
H=I(s)w(s) + mr^2w(g)
I(s)= segments moment of inertia w(s)= segments angular velocity m= segments mass r= distance between total body and segmental CGs w(g)= angular velocity of segmental CG about the principal transverse axis
What is the radius of gyration and what does it account for?
I=mk2,Distance from the axis of rotation to a point where the body's mass could be concentrated without altering its rotational characteristics.
What is moment of inertia and what are the two primary components?
I=mr2,Inertial property for rotating bodied representing resistance to angular acceleration; based on both mass and the distance the mass is distributed from the axis of rotation.
Which type of equipment provides constant velocity?
Isokinetic
What determines the ideal mechanical advantage of a pulley or pulley system?
It is equal to the number of rope sections supporting the load being lifted
Which of the following accurately describes the radius of gyration of the forearm segment?
It is greater with respect to the wrist than with respect to the elbow
Which of the following accurately describes the radius of gyration of the forearm segment?
It is greater with respect to the wrist than with respect to the elbow.
what is Conservation of Angular Momentum?
It is the total angular momentum of a given system remains constant in the absence of external torques. Useful in mechanical analysis of diving, and gymnastics events in which the human body undergoes controlled rotations while airborne.
How does "choking up" on a bat make it easier to swing
It reduces the bat's moment of inertia with respect to the axis of rotation at the player's wrists, and increases the relative ease of swinging.
what three factors affect the magnitude of angular momentum?
Its magnitude affected by body's mass (m), the distribution of that mass with respect to the axis of rotation (k), and the angular velocity of the body (ω).
Magnus Force
Lift force created by spinning object
Magnus Effect
Lift force that is created by spinning objects. Deviation in the direction of a spinning object towards the direction of the spin. (the effect from molecules of a fluid moving faster on one side than the other)
Which structure can handle to greatest amount of strain? (tendon, ligament, bone)
Ligament (can handle greatest amount of strain)then tendon - then bone -
Axis of Rotation
Line about which the lever revolves, which passes through the fulcrum and which is also at right angles to the plane of motion -
Rotating around which of the following principe axes of rotation has the least moment of inertia (anatomical position)?
Longitudinal
What affect does air pressure have on air density?
Lower pressure means lower density (high elevation). Higher pressure means higher density (low elevation). Fluid pressure accounts for most of fluid density.
Factors affecting stress to tissues
Magnitude of force Area of force distribution - Direction of force - Frequency - Loading rate -
Moment of inertia is the angular analogue of what?
Mass
How does the swinging of a baseball bat relate to this?
Mass and the distribution of mass with respect to the axis of rotation
why is this advantageous?
Mass distribution closer to the hip, with more massive thighs and slimmer lower legs than others Greatly reduces the moment of inertia of the leg with respect to the hip, thus reducing resistance to hip flexion and increasing angular acceleration
What is the involvement of newtons first law in human movement?
Mass remains constant which forms the underlying basis for the principle of conservation of angular momentum is that it remains constant. Angular momentum remains constant in the absence of external torque because angular velocity may change to compensate for changes in moment of inertia resulting from alterations in radius of gyration.
Factors that affect stability
Mass, friction, horizontal position and height of center of gravity with respect to the base of support
Regarding moment of inertia of the leg with respect to the hip, which of the following leg morphologies would favor a sprinter?
Massive thighs and slimmer lower legs
mechanical advatage
Mechanical Advantage = the ratio of the resistance force to the effort force of the lever (MA = R/E)
Mechanical advantage
Mechanical advantage is gained through the use of a mechanical device to increase or multiply the applied force
What does it mean if the effort arm is longer than the resistance arm?
Mechanical advantage toward STRENGTH
What does it mean if the effort arm is shorter than the resistance arm?
Mechanical advantage toward speed and range of motion.
Is gait different during walking when compared to sprinting?
Minimal angular accel of the legs is required. Flexion at the knee during swing phase remains relatively small, and the leg's moment of inertia with respect to the hip is relatively large.
Which of the following are accurate units for centripetal force?
N
Which of the following variables affects angular momentum?
Neither linear velocity or angular acceleration
The statement "a rotating body will maintain a state of constant angular motion unless acted on by an external torque" refers to which of the following?
Newton's first law of inertia
Newton's First Law applied to angular motion
Object's resistance to angular motion
Yakovlev's Model
Observed body's reaction to stresses and applied those reactions to appropriate training. (there is an appropriate amount of timing of training stimulus)
When a cyclist rounds a curve, where does centripetal force act?
On the tires of the cycle
Backspin
On top: higher speed and lower pressure of air. On bottom: lower speed and higher pressure on bottom. Makes ball curve upward.
Topspin
On top: lower speed and higher pressure. On bottom: higher speed and lower pressure. Makes ball curve downward.
How come gravity foes not affect angular momentum?
Perpendicular distance, and torque equal 0
Moment Arm
Perpendicular distance. For any given muscle, the moment arm is greatest when the angle of the pull of the bone is 90 degrees. (90 degrees from the bone it inserts on)
what makes a change in angular momentum on a spring board?
Position of fulcrum with respect to the tip of the board can usually be adjusted & can influence performance.Setting fulcrum farther back from tip of the board results in greater downward vertical velocity at the beginning of takeoff, which allows the diver more time in contact with the board to generate angular momentum and increased vertical velocity. -
Electromyography
Provides information on amplitude and frequency of electrical potential changes, which provides information about muscle activation. Picks up activity of multiple motor units. Electromyographs fluctuate around zero.
Root Mean Square
Provides sense of how active a muscle is. Its overall amplitude of activity. (square data, sum it, divide by number of observations, take square root of result)
What is angular momentum and what are the two primary components?
Quantity of angular motion possessed by a body; measured as the product of moment of inertia and angular velocity.
What is angular momentum, what is its formula?
Quantity of angular motion possessed by a body; measured as the product of moment of inertia and angular velocity. H = Iω or H = mk^2ω -
characteristics of torque arms
RA = FA: Both R and F move same distance FA > RA: More force generated - -Less force needed FA must move farther - RA > FA: More speed and range of motion RA moves farther - -Greater resistance or resistance arm requires greater force or longer force arm - cont. - If the forces (R & F) act at angles other than at right angles to the lever, the corresponding torque arms must be determined by projecting lines which intersect at right angles with the force lines.
Centripetal force is related to which of the following?
Radial acceleration
If a diver goes from a full layout position to a tub position, what will happen to his momentum?
Remain the same
Second Class Lever
Resistance arm is between the fulcrum and the effort arm. Example: toe raise (when standing on tip toe, the ball of the foot acts as the fulcrum, the weight of the body acts as the resistance, and the effort comes from the gastrocnemius muscle)
Second class levers
Resistance lies between the force and the Axis (fulcrum) A-R-F - Force arm always longer than the resistance arm -
Components of a Lever
Rigid bar: Not always straight
According to Newton's 2nd Law, what is the relationship among torque, moment of inertia, and angular acceleration?
T=Ia
What factors affect the magnitude of force relative to fluid?
Size, shape, surface material, velocity, density
How can a cyclist maintain balance when rounding a sharp curve?
Slow down, and lean to the inside of the curve
Fiber Type
Slow twitch fatigue resistant (least power) Fast twitch fatigue resistant (intermediate power) - Faster twitch fatigue resistant (intermediate power) Fastest twitch fatigue resistant (most power) -
levers and torque with sports
Sport skills generally incorporate several levers. The longer the lever (total segments), the more effective it is in imparting force. The greater the length of the lever, the greater the velocity and acceleration that occur at the distal end of the lever. -
Procedure for Jackson Strength Evaluation System- (Levers Experiment)
Strap on hand or on wrist. Used same equipment from the muscle strength test.
Shear
Stress that act perpendicular to long axis of structure (pulling across transverse plane--not very common)
Compression
Stress that acts parallel to long axis of structure and tends to shorten structure (weight bearing activities)
Tension
Stress that acts parallel to long axis of structure and tends to stretch the structure
Torque formula
T = Fd⊥
According to Newton's 2nd Law, what is the relationship among torque, moment of inertia, and angular acceleration?
T = Iα
newtons second law angular
T= Ia a net torque produces angular acceleration of a body that is directly proportional to the magnitude of the torque, in the same direction as the torque, and inversely proportional to the body's moment of inertia the greater moment of inertia, the smaller the angular acceleration
T = Fd⊥ label parts
T= Torque F= applied force d⊥ = force's moment arm or perpendicular distance from forces line of action to the axis of rotation
equation for torque
T=Fd
What does the patella (kneecap) do?
The knee cap increases mechanical advantage because it pulls the tendon farther from the joint axis. This increases the length of the effort arm, which gives you more strength.
Resistance Force
The load that must be overcome for motion to occur. (can be external weight, force of gravity) (output force)
how do we find the location of the center of gravity for a one-segment object, like a baseball bat/broom/shovel?
The location of the CG for a one-segment object, such as a baseball bat, a broom, or a shovel, can be approximately determined using a fulcrum to determine the location of a balance point for the object in three different planes.
Force Lever
The mechanical advantage favors force over speed when the force arm is bigger than the resistance arm A first class lever can be a force lever and a second class lever is always a force lever.
Speed Lever
The mechanical advantage favors speed over force when the resistance arm is bigger than the force arm. A first class lever can be a speed lever and a third class lever is always a force.
what is the mechanical advantage?
The mechanical effectiveness of a lever for moving a resistance
Explain the principle of the conservation of angular momentum.
The more closely concentrated the mass is to the axis of rotation, the easier it is to swing the object. the more mass is positioned away from the axis of rotation, the more difficult it is ti initiate (or stop) angular motion.
The more closely concentrated the mass is to the axis of rotation, the easier it is to swing it.
The more mass is positioned away from the axis, the more difficult it is to initiate or stop angular motion
how do throwing events relate to change in angular momentum?
The objective in throwing events is to maximize the angular impulse exerted on an implement before release to maximize its momentum and horizontal displacement following release.As long as the moment of inertia of a rotating body remains constant, increased angular momentum translates to increased linear momentum when the body is projected.
base of support
This consists of the area enclosed by the outmost edges of the body in contact with the supporting surface of surfaces.
How many principles axes are there for the human body?
Three
three conditions for equilibrium
Three conditions for equilibrium: Fv = 0 (sum of the vertical forces) Fh = 0 (sum of the horizontal forces) T = 0 (sum of torques)
What is drag force in swimming.
Thrust. Drag force in swimming is beneficial. Becomes a positive drag force that accelerates swimmer forward.
Neural Factors
Timing of firing rate of muscles affects force production and for how long.
Functions of machines
To balance forces t o enhance force - To enhance range of motion and speed - To alter direction -
What is the purpose of the upper body when running?
To counter the rotations of the lower body (Newton's 3rd law)
Why are golf club heads weighted?
To increase the moment of inertia of the club head rotating around the shaft
how does a Cyclist running a curve exerts CF on the tires to stay within a curved path?
To prevent rotation toward the outside of the curve, cyclist must lean to the inside of the curve so that the moment arm of the systems weight relative to contact point with the ground is large enough to produce an oppositely directed torque of equal magnitude. If no leaning, cyclist would have to reduce speed to reduce the magnitude of the ground rxn force, in order to prevent loss of balance. -
Why does a figure skater cross his arms tightly across the chest when preforming a quadruple axel?
To reduce moment of inertia, and to increase angular velocity
Torque
Torque is created when a force is applied at some distance from the axis of rotation. Torque=force*perpendicular distance. Units for torque are Nm. When a torque is applied angular acceleration is the result.
Impulse Momentum Relationship
Torque*change in time = Change in Angular momentum. If there is no impulse the momentum will be constant
Newton's 2nd Law applied to Angular Motion
Torque=angular inertia*angular acceleration
Terminal Velocity
Ultimate speed that can be attained when falling under the influence of gravity. When drag force(+all other frictional forces)=force of gravity. Sum of all forces are in equilibrium.
Fast Fourier Transform
Used to calculate multiple frequencies present in electromyography. (multiple frequencies are provided and shown on a power spectrum graph)
Buoyancy
Vertical or upward force on an object in fluid. It equals the weight of the fluid displaced by the object. It is a static force, which means buoyancy will occur whether an object is in motion or not.
why is the human body moment of inertia defined by the axis of rotation?
When segment rotates around the longitudinal axis, moment of inertia is different from its moment of inertia during flexion and extension or abduction and adduction, because mass distribution and its moment of inertia is different with respect to the axis of rotation.
How is swinging a bat related to using newtons third law?
When a baseball player forcefully swings a bat, rotating the mass of the upper body, a torque is created around the players longitudinal axis. if feet aren't firmly planted, the lower body tends to rotate around the longitudinal axis in the opposite direction. If feet are planted, the torque generated by the upper body is translated to the ground, where the earth generates a torque of equal magnitude and opposite direction on the cleats of the batters shoes.
How is Newton's 3rd law applied to a baseball player?
When a baseball player swings a bat, his arms and upper body rotate toward the pitcher. If his feet were not planted on the ground, his lower body would rotate in the opposite direction.
explain why handling a bat by the barrel results in short radius of gyration
When a bat is held by the barrel, radius of gyration is much shorter than when the bat is held properly because more mass is positioned close to the axis of rotation.
What happens when a jumper raises their legs?
When a jumper raises their legs, the rest of the body will drop lower (body position changes around center of mass during flight but center of mass stays on the same path)
when a muscle crossing a joint develops tension, what does it produce?
When a muscle crossing a joint develops tension, it produces a force pulling on the bone to which it attaches, thereby creating torque at the joint the muscle crosses.
How does the example of performing a one-and-a-half somersault dive exhibit the conservation of angular momentum?
When angular momentum is conserved, changes in body configuration produce a trade-off between moment of inertia and angular velocity, with a tuck position producing greater angular velocity.
What happens to centripetal acceleration and centrifugal force when a hammer thrower increases the angular velocity of the hammer?
When angular velocity of the hammer is increased,
explain the distribution of mass in a baseball bat of how it would resist angular acceleration?
When mass is closer to the axis of rotation, the easier it is to swing the bat.
how is spiking in volleyball related to conservation of angular momentum?
When performing a spike, moving the hitting arm with a high angular velocity and a large angular momentum, there is rotation of the lower body producing an = amount of angular momentum in the opposite direction. The moment of inertia of the 2 legs with respect to the hips is much greater than the spiking arm with respect to the shoulder. Angular velocity of the legs generated to counter the angular momentum of the swinging arm is much less than the angular velocity of the spiking arm.
How do you change the direction of an object when it has angular momentum?
You need to add torque. Torques may not change the magnitude of angular velocity of an object but it can change the components (can change the direction, inertia)
In which of the following situations is maximal stability desirable?
a Sumo wrestler's crouched defensive stance
Which one of the following incorrectly identifies the parts of a lever within the human body?
a bone is the rigid bar a joint is the axis of rotationa muscle insertion provides the point of force COM of the moving segment is the point of resistance
an example of a compound machine.
a car a washing machine a watch
Same as above, but with a volleyball spike,
a compensatory rotation of the lower extremity offsets the forcefully swinging arm so that total body angular momentum is conserved. -
what type of lever is your head?
a first class weight of head in the front going down fulcrum is the neck force of muscle pulling down in the back
what type of scenario would produce no torque?
a force directed through an axis of rotation because the force's moment arm is zero
what is good about when the mechanical advantage is greater than 1?
a force less than the resistance force is needed to move the object. it is good for heavy objects, but you do not move the object as far
when the mechanical advantage is less than 1 ______
a force that is larger than the resistance must be applied to cause motion to the lever. this is less effective in the sense that more force is requried, but a small movement of the lever will cause a larger range of motion
segmental method of locating the center of gravity
a procedure for determining total body center of mass location based on the masses and center of mass locations of the individual body segments The segmental method uses data for average locations of individual body segments CGs as related to a percentage of segment length The location of the CG of a multi-segmented object is more influenced by the positions of the heavier segments than by those of the lighter segments. A commonly used procedure for estimating the location of the total body CG from projected film images of the human body.
newtons first law angular
a rotating body will maintain a state of constant rotational motion unless acted on by an external torque conservation of angular momentum angular momentum will remain constant in the absence of external torque
lever
a simple machine consisting of a relatively rigid bar-like body that may be made to rotate about an axis
how to find center of gravity using a reaction board
a specially constructed board for determining the center of gravity location of a body positioned on top of it The procedure requires the use of a scale, a platform of the same height as the weight surface of the scale, and rigid board with sharp supports on either end. Location of the CG of the human body is complicated be the fact that its constituents (such as bone, muscle, and fat) have different densities and are unequally distributed throughout the body.
Anterior-posterior axis
a straight line that cuts through the body from front to back (lateral abduction and adduction of the arm)
Longitudinal axis
a straight line that cuts through the body from top to bottom (turning head side to side)
balance
ability to control equilibrium
rotary component
acting perpendicular to the bone actually causes the bone to rotate about the joint center
Plastic Region
after the yield point. Tissue is at risk for long term damage. The tissue has deformed and will not return to original shape even after stress is released.
much of human movement involves simultaneous tension development in ______ and _______ muscle groups.
agonist and antagonist
Agonist vs. Antagonist muscles
agonist: contracting muscle antagonist: stretching muscle agonist vs antagonist joint torques antagonist creates torques in direction opposite than the torques created by the agonist
For any given muscle, the moment arm is largest when the angle of pull on the bone is closest to
angle of *pull at 90 degrees*
Angular Acceleration
angular acceleration in angular kinematics: change in angular velocity/change in time, angular acceleration in angular kinetics=torque/angular inertia, Units: radians/second^2
Which of the following acts to produce a change in angular momentum?
angular impulse
In throwing event in track and field, the object is to... maximize the ___ exerted on an implement before release, to maximize its ___ and the ultimate ___ following release
angular impulse momentum horizontal displacement
angular impulse equation
angular impulse= Tt T= product of torques t= time interval
Which of the following is referred to as the "quantity of angular motion" possessed by a body?
angular momentum
Which of the following quantities increases as moment of inertia decreases during the airborne phase of a dive?
angular momentum and angular velocity
When the line of action of a body's weight (directed form the CG) moves outside the base of support, a torque is created that tends to cause ____
angular motion of the body, thereby disrupting stability, with the CG falling toward the ground.
In the absence of external torque, which of the following will increase when moment of inertia decreases?
angular velocity
1st class lever
axis (A) between force (F) & resistance ® - f-a-r -
Fulcrum
axis of rotation
The ability to control equilibrium defines ____________.
balance
The ability to control equilibrium defines what?
balance
local term
based on segment's angular momentum about its own segmental CG
inertia
body's tendency to resist acceleration a body's inertia is directly proportional to its mass
Which of the following is known as "center-seeking" force?
centripetal force
angular impulse
change in angular momentum equal to the product of torque and time interval over which the torque acts
what is Angular impulse?
change in angular momentum equal to the product of torque and time interval over which the torque acts. When it acts on a system, it results in a change in the total angular momentum of the system.
Angular velocity
change in displacement/change in time
Loading rate
change in force/change in time (impact sports have high loading rates to they require pads and helmets)
inertial property
characteristics that make something resistant to change or motion
If total body angular momentum is 0, what will happen as the result of a forceful movement such as a spike?
compensatory rotation in lower body in opposite direction
When net muscle torque and joint movement occur in the same direction, what type of contraction occurs?
concentric
dynamic equilibrium
concept indicating a balance between applied forces and inertial forces of a body in motion Bodies in motion are considered to be in a state of dynamic equilibrium, with all forces resulting in equal and oppositely directed inertial forces. dynamic equilibrium equations (sigma)Fx - māx = 0 (sigma)Fy - māy = 0 (sigma)TG - ī(alpha) = 0 The sums of the horizontal and vertical forces acting on a body are Fx and Fy; max and may are products of the body's mass and the horizontal and vertical accelerations of the body's center of mass; TG is the sum of torques about the body's center of mass, and I(alpha) is the product of the body's moment of inertia about the center of mass and the body's angular acceleration.
Which of the following is/are function(s) of antagonist muscles?
control velocity of movement and enhance stability of the joint
Angular Kinematics
description of angular motion
moment of inertia for human body
different with respect to different axes when the entire human body rotates free of support, it moves around one of 3 principal axes
inertia and mass
directly proportional the greater a body's mass, the greater its resistance to linear acceleration the greater a body's mass, greater resistance to angular acceleration as well
resistance arm
distance between the axis and the point of resistance application
what is the Radius of gyration?
distance from the axis of rotation to a point where the body's mass could be concentrated without altering its rotational characteristics and it can change as the axis of rotation changes.
radius of gyration
distance from the axis of rotation to a point where the body's mass could be concentrated without altering its rotational characteristics distance from axis of rotation to a point at which the mass of the body can theoretically be concentrated without altering the inertial characteristics of the rotating body
k
distance known as radius of gyration
most important factor for angular momentum
distribution of mass with respect to the axis of rotation bc H is proportional to the square of radius of gyration
additional factor for resisting angular acceleration
distribution of mass with respect to the axis of rotation will ease of swinging a bat be greater with weight near the bat's grip or end of bat?
how does motions of body segments during takeoff for a diver determine the magnitude and direction of the reaction force generating linear and angular impulse?
divers using their arms to contribute more to angular momentum than the motion of other segments. Divers use arm swings with the arm fully extended to maximize moment of inertia of the arms and angular momentum generated. Less skilled divers use flexion at the elbow to reduce the moment of inertia of the arms about the shoulders so that arm swing can be completed during the time available.
Pronation of foot
dorsiflexion, eversion, subtalar joint abduction
Where is radius of gyration located in relation to center of gravity (COG)?
further from the axis
A thin wedge of a given length has a(n) ________________ advantage than a thick wedge of the same length.
greater
The greater the amount of friction is between an object and the surface or surfaces it contacts, the _____ is the force requirement for initiating or maintaining motion
greater
The more massive an object is, the _____ is the force required to produce a given acceleration
greater
the higher the CG, the _______ stable you are
greater disruptive torque, less stable
what is good about when the mechanical advantage is less than 1?
greater force than the force of resistance is needed, but less force creates a further range of motion
when mass within an object is not constant, the COG shifts in the direction of the
greater mass
whenever the moment arm of the force is longer than the moment arm of the resistance, the mechanical advantage reduces to a number ______ meaning
greater than 1 meaning the magnitude of force needed to move the resistance is less than the resistance itself
radius of gyration and radius of rotation
gyration is always anger than the radius of rotation (distance to the segmental CG) radius of gyration changes as axis of rotation changes
Which will yield better results: low frequency/high stress or high frequency/low stress?
high frequency/low stress (but there is still risk for injury--need to know how much damage is being done and how much remodeling needs to happen between workout sessions.)
Asymmetrical positioning of the arms with respect to the axis of angular momentum can shift the axis of rotation. this is called ___
hula movement
Screws with threads that are close together have a greater________________________________
ideal mechanical advantage (IMA)
the mechanical advantage of a machine in the absence of friction is
ideal mechanical advantage (IMA)
angular momentum and angular velocity relationship
if body has no angular velocity, it has no angular momentum
Which of the following is true of a baserunner weighing 70 Newtons and a baserunner weighing 50 Newtons?
if the baserunners run at the same velocity around the bases, the heavier baserunner will have to lean in more towards the pitcher's mound due to a greater centripetal force
factors that increase mechanical stability
make you MORE stable (mass, friction, base of support, horizontal positioning, and vertical positioning) 5 - 1-Increasing body mass 2-Increasing friction between the body and the surface 3-Increasing the size of the base of support in the direction of the line of action of an external force 4-Horizontally positioning the center of gravity near the edge of the base of support on the side of the oncoming external force 5-Vertically positioning the center of gravity as low as possible
Moment of inertia is the angular analogue of what?
mass
Density
mass/volume
Regarding moment of inertia of the leg with respect to the hip, which of the following leg morphologies would favor a sprinter?
massive thighs and slimmer lower legs
The mechanical effectiveness of a lever for moving a resistance may be expressed quantitatively as its ______________which is the ratio of the moment arm of the force to the moment arm of the resistance:
mechanical advantage
The ratio of force arm to resistance arm defines _______________.
mechanical advantage
The relative efficiency of a lever is proportional to which of the following?
mechanical advantage of the lever
The perpendicular distance between the line of force and the axis defines what?
moment arm
Torque is the product of force and the perpendicular distance from the force to the axis, also known as the ___________________________.
moment arm
Mechanical Advantage (MA)
moment arm (force)/moment arm (resistance) ratio of the distance of the moment arm of the force, to the distance of the moment arm of the resistance
what does it mean when the mechanical advantage is greater than 1?
moment arm of force>moment arm of resistancea force can balance a larger resistance a force less than the resistance force is needed to move the object
As a joint moves through a range of motion, there are changes in the ______
moment arms of the muscle crossing the joint. to keep torque of muscle at a joint constant, you have to add more force if you decrease the moment arm
Which of the following phrases is/are synonymous with torque?
moment of force and rotary force
inertial property for angular motion
moment of inertia
I= Emr^2
moment of inertia for a body formula - I=mk^2
I
moment of inertia with respect to an axis
what does it mean when the mechanical advantage is less than 1?
moment of resistance is > than moment of force a force can move a resistance further range of motion with less force force greater than the force of resistance is needed, but a smaller force leads to a further distance traveled
Which of the following quantities is zero for an object in static equilibrium?
momentum kinetic energy
The more rotations or twists, the ___ angular momentum required
more
distribution of mass to axis of rotation and angular motion relationship
more closely concentrated the mass is to axis of rotation, EASIER to swing more mass positioned away from axis of rotation, more DIFFICULT to make angular motion OVERALL- the more closely mass is distributed to axis of rotation, the easier it is to initiate or stop angular motion
If disruption of stability is the desired outcome, which of the following should be observed?
move COM to edge of BOS
The ability to move a resistance with a force that is smaller than the resistance offers a clear advantage for
moving a heavy load
when the muscle is closer to the joint, how does it impact movement?
muscle closer to the joint moves the joint faster/makes more of an impact
force couple
muscle groups moving together to produce movement around a joint two forces acting in opposite directions to rotate a part around an axis
A simple machine consisting of a rope fitted into a groove in a wheel is a(n) __________________ .
pulley
angular momentum
quantity of angular motion possessed by a body measured as the product of moment of inertia and angular velocity
what is Angular Momentum?
quantity of angular motion possessed by a body. measured as the product of moment of inertia and angular velocity.
momentum
quantity of motion that an object has amount of motion
Since antagonist tension development creates torque in the direction opposite that of the torque produced by agonist, the resulting movement at the joint is a function of the _____
net torque
Does swinging with a weighted bat increase post-warm-up velocity?
no
Which of the following variables affects angular momentum?
not linear velocity or angular acceleration
Recruitment Rate
number of motor units stimulated by a neural system (increases number of units recruited, increased number on actin and myosin binding sites, increased active muscle force) -
how is transferring angular velocity from on principal axis to another can occur when a diver changes from a somersault rotation to twisting?
occurs through the vector sum of the 2 rotations if it remains constant in magnitude and direction. When total -body angular momentum is zero, generating a twist in midair is possible using skillful manipulation of a body composed of at least 2 body segments. Its easier to initiate rotation about long axes because total body movement of inertia with respect to the long axis is much smaller than the other 2 axs.
When a cyclist rounds a curve, where does centripetal force act?
on the tires of the cycle
the distance between the fulcrum in a lever and the output force
output arm
to calculate the ideal mechanical advantage of any lever, divide the input arm by the____________
output arm
the force exerted BY a machine
output force
When the human body acts as a projectile, the body's CG follows a ________, regardless of any changes in the configurations of the body segments while in the air.
parabolic trajectory
Strain
percent change in length (strain usually results from stress. when force is applied to a biological structure, stress results and may cause the structure to deform)
Movement/torque arm
perpendicular distance from the line of force to the axis of rotation
Supination of foot
plantar flexion, inversion, subtalar joint adduction
What effect does "choking up" on a bat have?
reduces moment of inertia and increases angular velocity of swing
Why do sprint coaches stress "heel to buttocks" during sprinting?
reduces moment of inertia of the leg with respect to the hip
Elastic Region
region a tissue can be stretched or changed shape to without damage (tissue will return to original shape after stress is released)
If a diver goes from a full layout position to a tuck position, what will happen to his momentum?
remain the same
2nd class lever
resistance (R) between axis (A) & force (F) - a-r-f -
second class lever
resistance is closer to the fulcrum/axis of rotation, force is towards the end (load=resistance, effort=force)
stability
resistance to disruption of equilibrium
What is the proposed advantage of Nautilus resistance equipment over free weights?
resistance varies over the range of motion with Nautilus equipment
When other factors remain constant, increased movement speed is associated with increased _______ during exercises such as the squat.
resultant joint torque
Transverse axis
runs from side to side across the body (bending forward at the hips, bicep curls)
wheelbarrow, nutcracker
second class lever
lower leg lever
second class. fulcrum is toe, force going down at the foot, effort going up in the back of the leg near calf
remote term
segment's angular momentum about the total body CG
What is the importance of segmental center of mass to the lever systems of the human body?
segmental COM is the point of resistance (where weight vector is drawn) and therefore determines the length of the resistance arm
how do we solve equilibrium problems?
set the torques equal to zero, or vertical components if you can find joint reaction force.
How can a cyclist maintain balance when rounding a sharp curve?
slow down and lean to the inside of the curve
The greater the moment of inertia, the ___ the resulting angular acceleration
smaller
the closer the cg to the outside of the base of support, the ______ stable
smaller less stable the closer the cg is to the outside of the board
Third class lever systems favor which of the following?
speed and range of motion
how do we find the resultant torque?
sum of each torque-make sure to designate direction tho (1 is negative and 1 is positive) Girl-190 N, moment arm=1.6 m boy-200 N, moment arm=1.5 m boy=clockwise girl=counterclockwise
The Greek letter sigma () means the
sum of, Fv represents vertical forces, Fh represents horizontal forces, and T is torque
When a discus thrower spins and then releases the discus, what direction will it travel?
tangent to the circular path at release
How can you increase the angular momentum of a golf club?
the goal for a golf swing is to transfer as much linear velocity to the ball as possible. A longer, heavier golf club swung with the same angular velocity as a shorter, lighter one will produce more angular momentum.
Resistance to angular acceleration is a function of a body's mass. The greater the mass
the greater the resistance to angular acceleration. However, the relative ease or difficulty of initiating or halting angular motion depends on the distribution of mass with respect to the axis of rotation.
in a 3rd class lever
the input force is between the output force and fulcrum, the IMA is always less than one
in a 2nd class lever
the load is between the fulcrum and the input force, the IMA is always greater than one
If mass is positioned away from the axis of rotation,
the more difficult it is to initiate (or stop) angular motion.
Which of the following affects the force-generating capability of a muscle?
the muscle length and cross-sectional area, the angle and distance from the joint center of the tendon attachment to bone, and the velocity of muscle shortening
Why does the orientation of a force acting on a body affect the amount of torque it generates at an axis of rotation within the body?
the orientation of the force acting on a body is related to torque because of the equation so to change the direction of the applied force you need to change the moment arm which will cause the torque to be changed
fulcrum
the point of support, or axis, about which a lever may be made to rotate
When a muscle contracts at a joint, which of the following affects torque?
the rotary component of muscle force
Define Torque
the rotary effect created by an applied force
torque definition
the rotary effect of a force about an axis of rotation. the product of the force and the force's moment arm vector quantity=magnitude and direction counterclockwise=positive clockwise=negative
A 30 kg child sits on the right end of a see-saw 1 m from the axis. If a 20 kg child sits on the left end of the see-saw 2 m from the axis, what will happen?
the see-saw will tilt to the left
what is the moment arm?
the shortest perpendicular distance from the force's line of action to the axis of rotation also referred to as the force arm or lever arm
When the elbow is extended and the elbow flexors contract, which of the component forces acts in addition to the rotary component?
the stabilizing component of muscle force
Which of the following must be true for an object to be in a state of static equilibrium?
the sum of all vertical forces acting on the object must be equal to zero the sum of all horizontal forces acting on the object must be equal to zero the sum of all torques acting on the object must be equal to zero
angular momentum for a segment about a principal axis equation
the sum of the local and remote terms
principle of conservation of momentum for angular motion
the total angular momentum of a given system remains constant in the absence of external torques
what contributes to net joint torque?
weight of bodies, motion of body segments, action of joint forces
When a cyclist rounds a curve, the gorund exerts ___ on the tires of the cycle. The forces acting on the cycle/cyclist system are ___, ___, and the ___. The ___ component of the GRF and laterally directed friction provide centripetal force, which also creates a(n) ___ about the system's CG. Cyclist must lean into curve to prevent rotation toward ___ of curve,centripetal force
weight, friction, GRF horizontal torque outside
