biomechanics midterm
Which of Newton's Laws of motion tells that the acceleration of an object is proportional to the force impressed?
2nd
Which of Newton's Laws of Motion can be described by 'action-reaction'?
3rd law
When a tennis player makes a cutting move and the shoe not moving relative to the surface, what type of friction is occuring?
Static
What is required for total mechanical energy to be conserved?
B: External forces must be in equilibrium
A: Graviational Potential Energy
The type of energy based upon an height
Total mechanical energy is conserved in which activity (ignore air resistance)?
C: A dismount from the bar in gymnastics while in the air
F slope- component of gravity
F Slope = Vertical Force x sin (angle of the slope).
A 67-kg skier glides down a 18 deg slope. There is a frictional force of 91 N and air resistance of 68 N. What is the resultant force working on the skier?
F= mgsinO-air resistance- friction force
law of universal gravitation
F=Gm1m2/r^2
flight time when it starts and ends the same
Ft=-2vy/g
Impulse-Momentum formula
Ft=mv
what forces affect projectiles?
Gravity and air resistance are the only forces that affect projectiles.
predicting horizontal position
HD= (FT)(Vh)
distance
How far the receiver travels
maximum height
Maximum height occurs when a projectile is halfway through the flight time from take-off until it returns to the height it left from. MH=Yo-vy^2/2g
Curvilinear translation
Motion along a curved path with no change in orientation. jumping but back and forth same distance but curved path
Rectilinear translation
Motion in a straight line with no change in orientation. riding a bicycle
To calculate changes in velocity after a collision where total momentum is conserved, we can use
Mv +mv = Mv+ MV
Law of Inertia
Newton's first law Inertia is the property of an object to resist changes in motion.
What is required for static equilibrium?
No motion and a resultant force of zero
normal force equation
Normal Force = Vertical Force x cos (angle of the slope).
Angular motion
Rotation of all points on an object around an axis pedling
Resultant Force (net force)
There are multiple forces at work. Internal forces include any force working within the body or object under investigation. External forces are those forces working outside the body. The overall effect of combining all the external forces working on an object is called a resultant or net force direction and magnitude
Newton's Second Law
This law is represented by the familiar equation F = ma. This law illustrates the cause and effect relationship of force and motion. Force causes motion. Additionally, Newton's second law tells us that the acceleration of the object is proportional to the amount of force that caused it and inversely proportional to the mass of the object. his law is often described as "action-reaction". This states that when an object exerts a force on another object, the second object exerts an equal (in magnitude) and opposite (in direction) force back on the original object. This law is particularly important when considering human locomotion.
impulse
This quantity of the average net force applied over a period of time (F*t) is known as Impulse.
Acceleration
When an object is speeding up, slowing down, or changing direction, it is accelerating. Acceleration is calculated using velocity (Equation 3 ). Acceleration can occur between components of velocity or in positive or negative directions
Equilibrium
When resultant external forces are calculated and add up to zero, the object is in equilbrium. This means the object will not accelerate
he Law of Universal Gravitation.
When the universal gravitational constant, the mass of the earth, and the radius of the earth are entered into this equation and calculated, the result is -9.8 m/s2.
vertical position is determined using what equation?
Y= Yo+Vyt+.5gt^2
The slope of velocity versus time equals
acceleration
g
acceleration due to gravity -9.8
Newton's first law states
an object at rest stays at rest unless acted upon by an outside force. Likewise, an object in motion stays in motion in a straight line unless acted upon by an outside force. A force must be applied to an object in order for it to move.
A gymnast doing a back flip is performing this type of motion:
anuglar motion
Velocity
based upon displacement rather than distance
Mechanical energy
can be defined as the ability to perform mechanical work. It is a scalar quantity that is, like mechanical work, measured in J. In this biomechanics context, we will discuss three forms of mechanical energy: (1) kinetic energy (KE), (2) gravitational potential energy (GE), and (3) strain potential energy (SE)
A ski jumper going for maximum distance is performing this type of motion while in the air:
curvilinear
Linear kinematics
description of motion
The difference between positive and negative work stems from the direction of motion of the body the force acts on and the
direction of the force acting on the body
speed equation
distance/time
that a state of equilibrium (Fresultant = 0)
does not necessarily mean that there is no motion. It just means there is not change in motion. Some other examples of constant motion when the resultant force is zero include: A gliding skater or hockey puck (very small amounts of friction) Lifting a dumbell at a constant velocity (here the lifting force equals the force of gravity providing a resultant force of zero).
Coefficient of Restitution Formula
e= V2-V1/U2-U1 has no units e= relative velocity after collision/relative velocity before collision
coefficient of restitution for bouncing a ball off the ground
e= square root of Hb/Hd
Sometimes an object that is not moving has all of the momentum of another object transferred into it. In this case, m2u2 and m1v1 can be removed from Equation 3 since the velocities in those terms are zero.
e=v2-v1/u2-u1
A car driving around a curve at a constant speed of 35 mph is not accelerating because the speed is constant.
false
When there are no external forces other than what are called conservative forces (gravity, elastic energy, electrical energy, and magnetic energy
he magnitude of total mechanical energy (i.e., the sum of kinetic, potential gravitational, and potential strain energy) does not change.
coefficient of restitution
he ratio of speeds after and before collisions. s a value that helps quantify the elasticity of an impact, by creating a ratio of relative velocities of the colliding objects before and after impact. The coefficient of restitution has no unit since it is calculated as a ratio of velocities.
Which quantity equals a change in linear momentum?
impulse
A soft foam pit is used for landing during the pole vault. The foam pit cushions the landing of the vaulter by
increasing the displacement during the landing
Mass is a measure of:
inertia
Vy=
initial vertical velocity
A resistance to a change in motion defines?
interia
mechanical work
is a scalar quantity that can be considered in two ways. Mechanical work relates to the ability of a force to (1) act through a given displacement, and (2) transfer mechanical energy. w=FD units -J
projectile
is an object that has been set on some path and continues on by its own inertia.
Linear momentum
is determined by an object's mass and the velocity at which it is traveling L=mv Newton's first law of motion is closely connected with momentum
Weight
is the downwards pull on an object due to its mass and gravity. On earth, gravity pulls on objects at about -9.8 m/s/s While weight depends upon how much gravity is generated by the location the object is, mass is constant no matter what the influence of gravity is.
Mass
is the measure of the inertia an object has. While weight depends upon how much gravity is generated by the location the object is, mass is constant no matter what the influence of gravity is.
power
is the rate at which mechanical work is performed and can be described using Mechanical power is an important characteristic of human motion, as it describes an individual's ability to perform mechanical work in a given duration. p=w/t=FV
When release velocity is doubled with a release height of zero and a release angle of 45 deg, what will happen to the horizotnal displacement?
it will qudruple
Which of the following is not a projectile?
jet plane
What is the branch of dynamics concerned with the description of motion?
kinematics
A projectile leaves from above the ground and lands on the ground. Assuming an equal magnitude of velocity, what will to optimal release angle be for maximum horizontal displacement (ignore air resistance)?
less than 45
The product of a body's mass and its linear velocity defines
linear momentum
flight time when staring and ending are different
long equation
elastic collision equation
m1v1+m2v2=m1v1+m2v2 m= mass U= velocities
normal force on slope
mg Cos theta
Which is an example of an internal force?
muscle force
mechanical work on bar
n summary, from the beginning to end of the repetition, zero mechanical work was done (negative in one direction and positive in the other)
normal force
n this case, "normal" will refer to the force which works perpendicular to the surface (a foot with the ground, a hand gripping a tennis racquet, the legs of a chair on the floor, etc).
elastic collisions,
objects bounce off of each other with the total momentum being conserved. In this type of collision, one object may gain momentum while the other loses momentum or both objects might keep the same momentum.
speed
pace of something
Y
predicted vertical
A skier going down a constant straight slope is performing this type of motion:
rectilinear
Combining components of forces leads to a:?
resultant force and Net force
Keep in mind that as you initially begin to lower the bar
the muscle force will be less than 445 N, however, as you near your chest, a muscle force that is greater than 445 N will be required to slow the descending bar, so that you don't hurt yourself.
inelastic collision
the objects collide and then stay together.
fricition
the resistance that one surface or object encounters when moving over another. This friction may be large or small, but will always be in existence. The magnitude of this frictional force is determined by how large the normal force is and a coefficient of friction F=uN
velocity equation
v=d/t
In the kinetic energy equation, which component is most influential should you change it?
velocity
The slope of a graph of position versus time will give:
velocity
Mechanical work of transfering energy
w= GPE+KE+SE mechanical work is equal to the change in total energy; in this context, total energy can be thought of as the sum of kinetic, potential gravitational, and potential strain energy
resultant force of runner
weight down * gravity air resistance and horizontal force going back same direction normal force going up. reduce and find angle or amount
To raise the bar,
you must apply an average upwards force of 445 N to the bar throughout an upwards displacement of 0.3 m (more than 445 N at the beginning of the motion and less than 445 N at the end of the motion).
strain energy
Potential strain energy is the ability to perform mechanical work, related to deformation, and can be defined using 1/2k(change in x)^2 (related to deformation)
Horizontal Displacement
After finding the flight time, horizontal displacement can be calculated by entering that flight time into HD= (ft)(vh)
General Motion
Any combination of at least two of the above types of motion.
Throughout the entire descent of the bar,
the average muscle force will be equal, but opposite, to the weight of the bar (445 N).
dynamic vs. static
Dynamic friction occurs when two dry surfaces are sliding between each other. When a shuffleboard puck glides across the board, dynamic friction is occuring. In contrast, a shoe on the ground while someone is running should not be moving relative to the surface providing an example of static friction.
Inertia
Inertia is a resistance to a change in motion.
Yo=
Initial vertical position
The type of energy based upon an object's motion
Kinetic Energy
kinetic energy
Kinetic energy is the ability to perform mechanical work, related to motion. Kinetic energy can be defined using 1/2mv^2
linear momentum equation
L=MV mass * velocity
What is true about mechanical work done to the body completed during a full repetition of a pushup?
Positive work is completed on the way up and negative on the way down equaling zero
gravitational potential energy
Potential gravitational energy is the ability to perform mechanical work, related to vertical position, and can be defined using -mgh
The slope of a position versus time graph equals
The slope of a position versus time graph equals velocity.
displacement
run began until where it finished represents vector quantity
The type of energy based upon deformation of an object
strain energy
Kinematics
study of describing movement (time, velocity, displacement)
Kinetics
study of forces that cause motion (force, torque, gravity, friction)
Newton's third law
that forces occur in pairs—every action has an equal and opposite reaction. Newton's law of gravitation helps us understand the force of gravity.
