Chapter 3 Biomechanics

Newton's second law! Law of acceleration

a change in the acceleration of a body occurs in the same direction as the faucet that caused it. the change in acceleration is directly proportional to the force causing it and inversely proportional to the mass of the body

as the force arm becomes longer,

a decreasing amount of force is required to move a relatively larger resistance

first class levers: if the force arm and the resistance arm are equal in length,

a force equal to the resistance is required to balance it.

wheels and axles function essentially as

a form of a lever

8) rotation about an axis aids balance

a moving bike is easier to balance than a stationary bike

a relatively smaller force may be applied to the wheel to move

a relatively greater resistance applied to the axle

in second class levers a large resistance can be moved by

a relatively small force

lever

a rigid bar that turns about an axis of rotation or a fulcrum

musculoskeletal system may be through of a as

a series of simple machines

to attain speed in moving the body,

a strong muscular force is generally necessary

balance:

ability to control equilibrium, either static or dynamic

to prevent injury or damage from tissue deformation the body must be used to

absorb energy from both internal and external forces

displacement:

actual distance that the object has been displaced from its original point of reference

distance:

actual sum length of measurement traveled

dynamic equilibrium:

all applied and inertial forces acting on the moving body are in balance, resulting in movement with unchanging speed or direction

statics involves

all forces acting on the body being in balance resulting in the body being in equilibrium

mass:

amount of matter in the body

in objects without a fixed axis it is

an applied force that is not in line with object's center or gravity

for rotation to occur what type of force must be applied?

an eccentric force

if either of the resistance components increase, there must be a/an (decrease/increase) in one or both of force components.

an increase

as the force arm becomes shorter,

an increasing amount of force is required to move a relatively smaller resistance

how are linear and angular motion are related in the body?

angular motion of the joints produces the linear motion of walking

shoveling-

application of lifting force to a shovel handle with lower hand while upper hand on shovel handle serves as axis of rotation

the longer the lever, from the natural body length of the body movement to the extended backward position, the greater will be the

arc through which it accelerates and thus the greater the speed imparted to the thrown object

if the radius of the wheel is 5 times the radius of the axle, then outside of the wheel with turn

at a speed of 5 times that of the axle

both the wheel and the axle complete the turn

at the same time

in the body joints represent what part of the lever?

axes

1st class lever

axis between the force and resistance FAR

humerus acts as the

axle

why can a tennis player hit a tennis ball harder with a straight arm drive than with a bent elbow?

because the lever (including the racket) is longer and therefore moves at a faster speed

why is the pull on the ulna considered direct and true?

because the ulna cannot rotate

static equilibrium:

body is at rest or completely motionless

what is an example of true 3rd class leverage?

brachialis

resistance application

center of gravity of lever or location of external resistance

single pulleys function to

change effection direction of force application

angular displacement:

change in location of a rotating body

first class lever systems produce force motion when axis is

close to resistance (crowbar)

first class levers produce speed and range or motion when axis is

close to the force (triceps in elbow extension)

any activity carried out at a steady pace in a consistent direction will

conserve energy

kinematics

description of motion and includes consideration of time, displacement velocity, acceleration, and space factors of a system's motion

stability is enhanced by

determining body's center of gravity and appropriately changing it

in the law of acceleration the change in acceleration is ____ proportional to the price causing it and _____ proportional to the mass of the body.

directly, inversely

resistance arm:

distance between the axis and the point of resistance application

linear displacement:

distance that a system moves in a straight line

in humans, contracting muscle applies what type of force to bone upon which it attaches?

eccentric force (not to be confused with eccentric contraction)

brachialis pulls on the ulna just below the

elbow

wheels and axles are used primarily to

enhance range of motion and speed of movement in the musculoskeletal system

6) in anticipation of an oncoming force, stability may be increased by

enlarging the size of the base of support in the direction of the anticipated force

using the lateral malleolus as a pulley, force is transmitted to the plantar aspect of the foot resulting in

eversion/plantar flexion

stronger and healthier tissues are more likely to withstand

excessive mechanical loading and the resultant excessive tissue deformation

tissue deformation may result from

external forces, but can result from internally generated forces

true or false: levers can be changed.

false. levers can not be changed, but they can be utilized more efficiently

the greater the force (mass x acceleration) that a person can produce, the

faster the arm will move, and thus the greater the speed that will be imparted to the ball

there are (few/many) 2nd class levers in the body

few

the biceps brachia supinates the forearm as it

flexes

Newton's third law! law of reaction:

for ever action there is an equal and opposite reaction

human leverage system is built for speed and range of movement at the expense of

force

motion cannot occur without

force

levers rotate about an axis as a result of _____ being applied to cause its movement against a _______.

force (effort, E), resistance

impulse in the product of

force and time

eccentric force:

force applied in direction not in line with the center of rotation of an object with a fixed axis

both the radius of the wheel and the radius of the axle correspond to the

force arms

3rd class lever

force between axis and resistance AFR

the greater the mass, the more

force needed to significantly change an objects inertia

friction:

force that results from the resistance between surfaces of two objects from moving up one another

to determine the amount of friction forces consider both

forces pressing the two objects together and the coefficient of friction

7) equilibrium may be enhanced by increasing the

friction between the body and the surfaces in contacts

with slick ground or shoe surface friction is (reduced/increased) and we are more likely to slip

friction is reduced

kinetic friction:

friction occurring between two objects that are sliding upon one another

ther center of the wheel and the axle both correspond to the

fulcrum

external forces are produced from outside the body and originate from

gravity, inertia or direct contact

internal rotators attaching to the humerus resulting in

greater range of motion and speed

force of the surface eating to the force we place on it is called

ground reaction force

if the radius of the wheel is 5 times the radius of the axle, then the wheel

has a 5 to 1 mechanical advantage over the axle

4) a person has balance, depending on the

height of the center of gravity -the lower the center of gravity, the more balance

speed:

how fast an object is moving or distance that an object moves in a specific amount of time

balance:

important in resting and moving bodies

momentum may be altered by

impulse

when do we desire decreased friction?

in skating so that we may slide across the ice with less resistance

velocity:

includes the direction and describes the rate of displacement

pulleys may be combined to form compound pulleys to

increase mechanical advantage

static friction may be increased by

increasing the normal or perpendicular forces pressing the two objects together such as in adding more weight one object sitting on the other object

what may cause these loads?

internal or external forces

what type of relationship is between the length of the lever arms?

inverse relationship -between force and force arm -between resistance and resistance arm

as peroneus longus contracts,

it pulls towards its belly (toward the knee)

what is an example of a pulley in the human body?

lateral malleolus acting as a pulley around which tendon of preens longus runs

which one of newton's laws is in effect with the muscular force necessary to accelerate the arm, wrist, and hand.

law of acceleration

in throwing, the individual's inertia and the ball's inertia must be overcome by the application of force. which of newton's laws is this?

law of inertia

rolling friction is always much (less/more) than static or kinetic friction

less

the longer the force arm, the (less/more) force required to move the lever if the resistance and the resistance arm remain constant.

less

triceps force arm is

less than 1 inch

what is the most common type of machine?

levers

in throwing, the angular motion of the levers (bones) of the body (trunk, shoulder, elbow and wrist) is used to give

linear motion to the ball when it is released

greater force or force arm allows a greater amount of resistance to be moved or a (shorter/longer) force arm to be used.

longer

greater resistance or resistance arm requires (shorter/longer) force arm.

longer

many activities, particularly upper extremity, require a summation of forces from the beginning of movement in the

lower segment of the trunk and movement at the shoulder, elbow and wrist joints

momentum is equal to

mass X velocity

resistance can vary from

maximal to minimal

strong muscle are able to produce more force than weak muscles both

maximum and sustained exertion over a period of time

what are the two equations for determining mechanical advantage?

mechanical advantage = resistance/ force or mechanical advantage= length of force arm/ length of resistance arm

what is another name for torque?

moment of force

shortening the resistance arm allows (less/more) resistance to be moved if force and force arm remain constant.

more

the greater the distance of the force arm, the (less/more) torque produced by the force.

more

curvilinear motion:

motion along a curved line

linear motion:

motion along a line

rectilinear motion:

motion along a straight line

short force arms and long resistance arms require great muscular strength to produce

movement

amount of torque is determined by

multiplying the amount of force (force magnitude) by the force arm

interntal force can only be activated by

muscles

what is the main source of force in the body?

muscles

what is the source of force in the human body?

muscular system

without forces acting on an object there would be

no motion

the body from the feet to the fingers can be considered as

one long lever

the reluctant to change status;

only force can change status

hand and wrist are located

outside of the wheel when the elbow is flexed 90 degrees

force arm:

perpendicular distance between location of force application and axis

what is an example of a second class lever system in the body?

plantar flexion of the foot to raise the body up on the toes

center of gravity:

point at which all of the body's mass and weight are equally balanced or equally distributed in all directions

axis

point of rotation about which lever moves

force:

produce of mass times acceleration

what is good about third class levers?

produce speed and range of motion in the body

what type of relationship is found between force components and resistance components?

proportional relationship

forces either

push or pull on an object in an attempt to affect motion or shape

what is an example of a 2nd class lever?

push up

what is another term for momentum

quantity of motion

mechanical advantage =

radius of the wheel/radius of the axle

we provide the action force while the surface provides the

reaction force

2nd class lever

resistance between axis and force ARF

in human movement, inertia refers to

resistance to acceleration or deceleration

inertia:

resistance to action or change

rolling friction:

resistance to an object rolling across a surface such as a ball rolling across a court or a tire rolling across the ground

the greater the momentum, the greater the

resistance to change in the inertia or state of motion

force x force arm =

resistance x resistance arm

what is another name for angular motion?

rotary motion

applying an eccentric force to a bone causes the bone to

rotate about an axis at the joint

balance or equilibrium is a factor in throwing when the body is

rotated posteriorly in the beginning of the throw

angular motion:

rotation around an axis

using the elbow joint as the axis, the biceps brachia applies force at its insertion on radial tuberosity to perform what action?

rotation of the forearm

what type of lever system is a push up?

second class, due to the axis being at the hand and the retsinas is body weight at the elbow joint

human leverage for sport skills requires

several levers

for quickness, it is desirable to have a

shorter lever arm

throwing a ball involves levers at

shoulder, elbow & wrist joints

body motion is produced or started by

some action of muscular system

it is advantageous to absorb force over later aspects of our body rather than smaller and to

spread the absorption rate over a greater period of time

to control equilibrium and achieve balance, ____ needs to be maximized.

stability

equilibrium:

state of zero acceleration where there is no change in the speed or direction on the body -static or dynamic

which is always greater static or kinetic friction?

static friction is always greater than kinetic friction -it is always more difficult to initiate dragging an object across a surface than to continue dragging

kinetics

study of forces associated with the motion of a body

mechanics:

study of physical actions of forces

dynamics

study of systems in motion with acceleration

statics:

study of systems that are in a constant state of motion, whether at rest with no motion or moving at a constant velocity without acceleration

short levers are advantageous in

taking less total time to release the ball

what in the body may generate passive internal forces

tension in tendons, connective tissues, ligaments and joint capsules

static friction:

the amount of friction between two objects that have no yet begun to move

mass:

the amount of matter in the body

first class levers produce balanced movements when

the axis is midway between the force and resistance (seesaw)

in the body bones represent what part of the lever?

the bars

5) a person has balance, depending on where the center of gravity is in relation to

the base of support -balance is less if the center of gravity is near the edge of the base -when anticipating an oncoming force, stability may be improved by placing the center of gravity nearer the side of the base of support expected to receive the force

biomechanics is necessary to study

the body's mechanical characteristics & principles to understand its movements

general factos applicable to enhancing equilibrium, maximizing stability, an ultimately achieving balance: 1) a person has balance when

the center of gravity falls within the base of support

what happens when the applied force exceed the amount of forearm resistance in an elbow?

the elbow extends

force equation in throwing a ball

the force applied to the ball is equal to the weight of the arms times the speed of acceleration of the arm

the greater the object's mass,

the greater its inertia

the longer the lever,

the greater the speed that can be imparted to the ball

depends upon

the hardness and roughness of the surface textures

example of a first class lever

the head balancing on the neck in flexing/extending -agonist and antagonist muscle groups are contracting simultaneously on either side of the joint axis -agonist produces force while antagonist supplies resistance

the reason of the feet against the surface on which the subject stands applies which law?

the law of reaction

the longer the lever,

the more effective it is in imparting velocity

when either the wheel or axle turn,

the other must turn as well

axis/fulcrum

the point of rotation

you calculate the mechanical advantage of the wheel and axle by considering

the radius of the wheel over the axle

acceleration:

the rate of change in velocity

coefficient of friction:

the ratio between force needed to overcome the friction over the force holding the surfaces together

the force arm can be described as

the shortest distance from axis of rotation to the line of action of the force

2) a person has balance in the direction proportion to

the size of the base -the larger the base of support, the more balance

mass affects

the speed and acceleration in physical movement

biomechanics:

the study of mechanics as it relates to the functional and anatomical analysis of biological systems, especially humans.

as we place force on a surface by walking over it,

the surface provides an equal resistance back in he opposite direction to the soles of our feet

significant mechanical loads are generated and absorbed by

the tissues of the body

what is torque?

the turning effect of an eccentric force

force equation

the weight of a body segment or the entire body X the speed of acceleration force= M x a

if the wheel raids is greater than the radius of the axle, then, due to the longer force arm,

the wheel has the mechanical advantage over the axle

if application of force is reversed and applied to the axle, then the mechanical advantage results from

the wheel turning a greater distance and speed

why do long levers produce better performance in sports?

they produce more linear force

what is the most common lever in the body?

third class levers

why do muscles contract?

to apply force

what are machines used for?

to increase mechanical advantage

Often, we purposely increase force arm length in order to increase torque so that we can more easily move a relatively large resistance. what is the purpose of this?

to increase our leverage

often, we purposely increase force arm length in order to increase _____.

torque

what is another name for linear motion?

translatory motion

what is an example of a 1st class lever?

triceps extension

true or false: Biceps brachii supinates forearm as it flexes so its 3rd class leverage applies to flexion only

true

true or false: all tissues, in varying degrees, resist changes in their shape

true

brachialis pulls on the

ulna

a system in acceleration is unbalanced due to

unequal forces acting on the body

what is the axis of rotation in the body?

various joints

any irregularly paced or directed activity will be

very costly to energy reserves

3) a person has balance depending on the

weight (mass) -the greater the weight, the more the balance

tendency for the current state of motion to be maintained, regardless of

where the body segment is moving at a particular velocity or is motionless

where is the force applied on a muscle?

where the muscle inserts in bone, not in the belly of muscle

force of application

(usually muscle insertion) effort

the force arm can also be known as

-moment arm -torque arm

what is an example of a third class lever?

-paddling a boat -shoveling -biceps brachii in elbow flexion

what are the two types of friction?

-static -kinetic

excessive tissue deformation due to mechanical loading may result from

-tension (stretching or strain) -compression -shear -bending -torsion (twisting)

9) kinesthetic physiological functions contribute to balance

-the semicircular canals of the inner ear, vision, touch (pressure) & kinesthetic sense all provide balance information to the performer -balance and its components of equilibrium and stability are essential in all movements and are all affected by the constant force of gravity as well as by inertia

what are some examples of second class levers?

-wheelbarrow -nutcracker -loosening a lug nut -raising the body up on the toes

each additional rope increased mechanical advantage by

1

what is the mechanical advantage of single pulley?

1

biceps force arm is

1 to 2 inches

what are the components of the third class lever system in elbow flexion at the biceps brachii (AFR)?

A= elbow joint F=biceps brachia applies force at its insertion on the radial tuberosity R=center of gravity serving as the point of resistance application

what are the components of the lever system (A, F, R) in plantar flexion?

A=ball of the foot F=plantar flexors apply force to the calcaneus R=tibial articulation with the foot

newton's first law! law of inertia

-a bod yin motion tends to remain in motion at the same sped in a straight line unless acted on by a force; a body at rest tends to remain at rest unless acted on by a force -muscles produce force to start, stop, accelerate, decelerate & change the direction of motion

there are three points that determine the type of lever and for which kind of motion it is best suited, what are these three points?

-axis -force application -resistance application

stability is the stability to a

-change in the body's acceleration -disturbance of the body's equilibrium

internal forces can

-fracture bones -dislocate joints -disrupt muscles & connective tissues

what are two other examples of third class levers?

-hamstrings contracting to flex leg at knee while in a standing position -using iliopsoas to flex thigh at hip

what are the three machine types not found in the body?

-inclined plane -screw -wedge

musculoskeletal sytem arrangement provides for 3 types of machines in producing movement:

-levers -wheel and axles -pulleys

what are the two types of motion?

-linear motion -angular motion

mechanical advantage

-load/effort or load divided by effort -ideally using a relatively small force, or effort to move a much greater resistance

machines function in 4 ways:

1) balance multiple forces 2) enhance force in an attempt to reduce total force needed to overcome a resistance 3) enhance range of motion & speed of movement so that resistance may by moved further or faster than the applied force 4) alter resulting direction of the applied force

what are the two divisions of mechanics?

1) statics 2) dynamics

the distance that the outside of the wheel turns will be

5 times that of the outside of the axle