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Biomechanical Factors Biomechanical Factors & & Concepts Concepts Chapter 3

Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

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Page 1: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Biomechanical Factors Biomechanical Factors

& &

ConceptsConcepts

Chapter 3

Page 2: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

• BiomechanicsBiomechanics: : – The study of The study of mechanicsmechanics as it relates to functional as it relates to functional

and anatomical analysis of biological systems.and anatomical analysis of biological systems.

– MechanicsMechanics: : • The study of physical actions of forces. Divided into:The study of physical actions of forces. Divided into:

– StaticsStatics: : the study of systems that are in a constant state of motionthe study of systems that are in a constant state of motion

• At rest with no motion or At rest with no motion or

• Moving at a constant velocity without accelerationMoving at a constant velocity without acceleration

• (Forces acting on the body being in balance)(Forces acting on the body being in balance)

– DynamicsDynamics: : they study of systems in motion with acceleration.they study of systems in motion with acceleration.

• (Unequal forces acting on the body causing it to be unbalanced)(Unequal forces acting on the body causing it to be unbalanced)

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Page 3: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

• Machines of the Body:Machines of the Body:– Used to increase or multiply the applied force Used to increase or multiply the applied force

(muscular contraction) in performing a task (to (muscular contraction) in performing a task (to cause, control, prevent cause, control, prevent →→ push, pull, hold) to push, pull, hold) to provide a provide a mechanical advantage.mechanical advantage.

• Mechanical advantage:Mechanical advantage:– Enables us to apply a relatively small force to move a Enables us to apply a relatively small force to move a

much greater resistancemuch greater resistance

– Determined by Determined by dividing load by effortdividing load by effort::

Page 4: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

• Machines function to:Machines function to:– Balance multiple forcesBalance multiple forces– Enhance forceEnhance force– Enhance range of motion and speed of movementEnhance range of motion and speed of movement– Alter the resulting direction of an applied forceAlter the resulting direction of an applied force

Page 5: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Musculoskeletal System Machines

• LeversLevers

• Wheel/AxlesWheel/Axles

• PulleysPulleys

Page 6: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Levers

Lever:Lever:– A rigid bar that turns around an axis of rotation, or fulcrum.A rigid bar that turns around an axis of rotation, or fulcrum.

– Three Points of a LeverThree Points of a Lever1.1. Axis (A):Axis (A):

• The point of rotation (joint) about which the lever movesThe point of rotation (joint) about which the lever moves

2.2. Force (F):Force (F):• The point of force application (usually muscle insertion)The point of force application (usually muscle insertion)

3.3. Resistance (R): Resistance (R): • The point of resistance applicationThe point of resistance application

• Center of gravity of lever orCenter of gravity of lever or

• Location of an external resistanceLocation of an external resistance

Humans move through a system of levers that cannot be changed, but can be used Humans move through a system of levers that cannot be changed, but can be used more effectivelymore effectively

Note: The arrangement of these three points determines the type of lever & which kind of motion it is best suited

Page 7: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

First Class LeverAxis (A) is between Force (F) and Resistance (R)

• If axis is midway between If axis is midway between force and resistance = force and resistance = – Balanced movementBalanced movement

• If axis is close to the force = If axis is close to the force = – Speed and range of motionSpeed and range of motion

• If axis is close to resistance =If axis is close to resistance = – ForceForce

Anatomical ExamplesAnatomical Examples

Head on Neck Triceps Press

• FARFAR1st1st

AA

FF RR

| Force ArmForce Arm || | Resistance Arm Resistance Arm ||

Page 8: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Second Class LeverResistance (R) is between Axis (A) and Force (F)

• Large resistance can be moved with relatively Large resistance can be moved with relatively small forcesmall force

• Designed to produce Designed to produce forceforce movements movements

Anatomical ExamplesAnatomical Examples

Heel Raises Push ups

• ARFARF2nd2nd

| | Force Arm Force Arm ||

AA

RR

| | Resistance Arm Resistance Arm ||

FF

Page 9: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Third Class LeverForce (F) is between Axis (A) and Resistance (R)

• Requires large force to move a relatively small Requires large force to move a relatively small resistanceresistance

• Designed for speed and range of motionDesigned for speed and range of motion• Most levers in the human body are this typeMost levers in the human body are this type

Anatomical ExamplesAnatomical Examples

Biceps Curl Knee Flexion

• AFRAFR3rd3rd

| | Resistance Arm Resistance Arm ||

AA

RR

| | Force Arm Force Arm ||

FF

Page 10: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Mechanical Advantage of Leversmay be determined using the following

equations:

• Mechanical Mechanical AdvantageAdvantage

= =

ResistanceResistance

ForceForce

• Mechanical Mechanical AdvantageAdvantage

==

Length of force armLength of force arm

Length of resistance armLength of resistance arm

Page 11: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Torque• Torque (moment of force) – the turning effect of an eccentric Torque (moment of force) – the turning effect of an eccentric

forceforce– Eccentric force: force applied in a direction not in line with the center Eccentric force: force applied in a direction not in line with the center

or rotation of an object with a fixed axis or rotation of an object with a fixed axis

– For rotation to occur, an eccentric force must be appliedFor rotation to occur, an eccentric force must be applied

– In the human body, the contracting In the human body, the contracting muscle applies an eccentric forcemuscle applies an eccentric force (not to be confused with an eccentric contraction) to the bone on (not to be confused with an eccentric contraction) to the bone on which it attaches and causes the bone to rotate about an axis at the which it attaches and causes the bone to rotate about an axis at the jointjoint

– The amount of torque can be determined by multiplying the The amount of torque can be determined by multiplying the amount amount of force by force armof force by force arm

Page 12: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Force Arm

• Force armForce arm: the distance between the location of : the distance between the location of force and the axisforce and the axis– Distance from joint to where the muscle attachesDistance from joint to where the muscle attaches

– Also known as moment arm or torque armAlso known as moment arm or torque arm

– The greater the distance of force arm, the more torque The greater the distance of force arm, the more torque produced by the forceproduced by the force

Page 13: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Resistance Arm

• Resistance ArmResistance Arm: the distance between the axis and : the distance between the axis and the point of resistance application the point of resistance application – Distance from joint to center of gravity of distal segmentDistance from joint to center of gravity of distal segment

Page 14: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Inverse Relationship Between Length of the Two Lever Arms

• Longer force arm = less force requiredLonger force arm = less force required

(assuming resistance and resistance arm are (assuming resistance and resistance arm are constant)constant)

• Shorter resistance arm = greater resistance movedShorter resistance arm = greater resistance moved

(assuming force and force are remain constant) (assuming force and force are remain constant)

Page 15: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Proportional Relationship Between Force & Resistance Components

• ↑ ↑ Resistance Resistance requiresrequires ↑ Force ↑ Force• ↑ ↑ Resistance arm length Resistance arm length requiresrequires ↑ Force arm length ↑ Force arm length• ↑ ↑ Force or force arm allows ↑ resistance to be Force or force arm allows ↑ resistance to be

movedmoved• Slight variations - impact on mechanical advantageSlight variations - impact on mechanical advantage

Page 16: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological
Page 17: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Human leverage System

• Built for Built for speed & ROM @ expense ofspeed & ROM @ expense of force force

• Short force arm & long resistance arm Short force arm & long resistance arm requiresrequires great strength to produce movementgreat strength to produce movement

• Longer lever arm = more effective in Longer lever arm = more effective in ↑↑ velocity velocity

Page 18: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

90°

90°

AMP

AR MFA

RFA

COG

Torque, Length of Lever Arms, Angle of Resistance & Angle of Muscle Pull

• EMC: Effective Muscular ComponentEMC: Effective Muscular Component• ERC: Effective Resistive ComponentERC: Effective Resistive Component

• Note: When working these problems determine:Note: When working these problems determine: – Type of muscle contractionType of muscle contraction

– Relative speed of movementRelative speed of movement

• EquationsEquations::– EMC = Muscular Force (MF) x Muscular Force Arm (MFA) x Sine of Angle of EMC = Muscular Force (MF) x Muscular Force Arm (MFA) x Sine of Angle of

Muscle Pull (AMP)Muscle Pull (AMP)

– ERC = Resistive Force (RF) x Resistive Force Arm (RFA) x Sine of Angle of ERC = Resistive Force (RF) x Resistive Force Arm (RFA) x Sine of Angle of Resistance (AR)Resistance (AR)

Example:

Muscular Force = 100

Resistive Force = 40

Muscular Force Arm = 2”

Resistive Force Arm = 10”

Angle of Muscle Pull = 90°

Angle of Resistance = 90°

Calculate EMC and ERC

EMC = MF x MFA x sin AMP

= 100 x 2” x sin 90°

= 200

ERC = RF x RFA x sin AR

= 40 x 10” x sin 90°

= 400

Eccentric Contraction – Fast movement

Page 19: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Wheels and Axles• Used primarily to enhance speed and range of Used primarily to enhance speed and range of

motion in the musculoskeletal systemmotion in the musculoskeletal system• Center of the wheel and axle both correspond to Center of the wheel and axle both correspond to

the fulcrumthe fulcrum• Both the radius of the wheel and the radius of Both the radius of the wheel and the radius of

the axle correspond to the force armsthe axle correspond to the force arms

• If a wheel radius is 3 times greater than the If a wheel radius is 3 times greater than the radius of the axle, due to the longer force radius of the axle, due to the longer force arm, the wheel has a mechanical advantage arm, the wheel has a mechanical advantage over the axleover the axle– The outside of the wheel will turn at a speed 3 The outside of the wheel will turn at a speed 3

times that of the axletimes that of the axle– The distance that the outside of The distance that the outside of

the wheel turns will be 3 the wheel turns will be 3 times that of the outside axletimes that of the outside axleJoint:

Axle:

Outside of Wheel:

Force:

Page 20: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Pulleys• Single pulleys have a fixed axle Single pulleys have a fixed axle

– function to change the effective direction of force function to change the effective direction of force application application

– have a mechanical advantage of 1have a mechanical advantage of 1

• Every additional rope connecting to moveable Every additional rope connecting to moveable pulleys increases the mechanical advantage by 1pulleys increases the mechanical advantage by 1

Joint:

Pulley:

Force:

Force Application:

Movement:

Page 21: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological
Page 22: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Laws of motion and physical activities

• Body motion is produced or started by some Body motion is produced or started by some action of muscular systemaction of muscular system

• Motion cannot occur without a forceMotion cannot occur without a force

• Muscular system is source of force in Muscular system is source of force in humanshumans

• TwoTwo types of motiontypes of motion– linear motionlinear motion– angular motionangular motion

Page 23: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Laws of motion and physical activities• Linear motion (translatory motion) - motion Linear motion (translatory motion) - motion

along a linealong a line– rectilinearrectilinear motion - motion along a straight line motion - motion along a straight line– curvilinearcurvilinear motion - motion along a curved line motion - motion along a curved line

• Linear displacementLinear displacement - distance that a - distance that a system moves in a straight linesystem moves in a straight line

Page 24: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Laws of motion and physical activities• Angular motion (rotary motion) - rotation Angular motion (rotary motion) - rotation

around an axisaround an axis– In the body, the axis of rotation is provided by In the body, the axis of rotation is provided by

the various jointsthe various joints

• Linear & angular motion are relatedLinear & angular motion are related– angular motion of the joints produces the linear angular motion of the joints produces the linear

motion of walkingmotion of walking

Page 25: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Laws of motion and physical activities• Sports ex. - cumulative angular motion of Sports ex. - cumulative angular motion of

the joints imparts linear motion to a thrown the joints imparts linear motion to a thrown object (ball, shot) or to an object struck with object (ball, shot) or to an object struck with an instrument (bat, racket)an instrument (bat, racket)

Page 26: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Laws of motion and physical activities• DisplacementDisplacement - actual distance that the - actual distance that the

object has been displaced from its original object has been displaced from its original point of referencepoint of reference

• DistanceDistance - actual sum length of - actual sum length of measurement traveledmeasurement traveled– object may have traveled a distance of 10 object may have traveled a distance of 10

meters along a linear path in two or more meters along a linear path in two or more directions but only be displaced from its directions but only be displaced from its original reference point by 6 meters original reference point by 6 meters

Page 27: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Laws of motion and physical activities

• Angular displacementAngular displacement - change in location of - change in location of a rotating bodya rotating body

• Linear displacementLinear displacement - distance that a system - distance that a system moves in a straight linemoves in a straight line

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

• VelocityVelocity - includes the direction & describes - includes the direction & describes the rate of displacementthe rate of displacement

Page 28: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Laws of motion and physical activities

• Newton's laws of motion have many Newton's laws of motion have many applications to physical education activities applications to physical education activities and sportsand sports

Page 29: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Law of Inertia• A body in motion tends to remain in A body in motion tends to remain in

motion at the same speed in a straight line motion at the same speed in a straight line unless acted on by a force; a body at rest unless acted on by a force; a body at rest tends to remain at rest unless acted on by tends to remain at rest unless acted on by a forcea force

• Muscles produce force to start, stop, Muscles produce force to start, stop, accelerate, decelerate & change the direction accelerate, decelerate & change the direction of motionof motion

Page 30: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Law of Inertia• InertiaInertia - resistance to action or change - resistance to action or change

– In human movement, inertia refers to resistance In human movement, inertia refers to resistance to acceleration or decelerationto acceleration or deceleration

– tendency for the current state of motion to be tendency for the current state of motion to be maintained, regardless of whether the body maintained, regardless of whether the body segment is moving at a particular velocity or is segment is moving at a particular velocity or is motionlessmotionless

– the reluctance to change status; only force can the reluctance to change status; only force can change statuschange status

Page 31: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Law of Inertia• The greater an object’s mass, the greater its inertiaThe greater an object’s mass, the greater its inertia

– the greater the mass, the more force needed to the greater the mass, the more force needed to significantly change an object’s inertiasignificantly change an object’s inertia

• ExamplesExamples– Sprinter in starting blocks must apply considerable force Sprinter in starting blocks must apply considerable force

to overcome his resting inertiato overcome his resting inertia– Runner on an indoor track must apply considerable Runner on an indoor track must apply considerable

force to overcome moving inertia & stop before hitting force to overcome moving inertia & stop before hitting the wallthe wall

– Thrown or struck balls require force to stop themThrown or struck balls require force to stop them

Page 32: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Law of Inertia

• Force is required to change inertiaForce is required to change inertia– Any activity carried out at a steady pace Any activity carried out at a steady pace

in a consistent direction will conserve in a consistent direction will conserve energyenergy

– Any irregularly paced or directed activity Any irregularly paced or directed activity will be very costly to energy reserveswill be very costly to energy reserves

– Ex. handball & basketball are so much Ex. handball & basketball are so much more fatiguing than jogging or dancingmore fatiguing than jogging or dancing

From Hamilton N, Luttgens K: Kinesiology: scientific basis of human motion, ed 10, 2002, McGraw-Hill.

Page 33: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Law of Acceleration• A change in the acceleration of a body A change in the acceleration of a body

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

Page 34: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Law of Acceleration• AccelerationAcceleration - the rate of change in velocity - the rate of change in velocity

– To attain speed in moving the body, a strong To attain speed in moving the body, a strong muscular force is generally necessarymuscular force is generally necessary

• Mass - the amount of matter in the bodyMass - the amount of matter in the body– affects the speed & acceleration in physical affects the speed & acceleration in physical

movementsmovements

Page 35: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Law of Acceleration• A much greater force is required from the muscles A much greater force is required from the muscles

to accelerate a 230-pound man than than to to accelerate a 230-pound man than than to accelerate a 130-pound man to the same running accelerate a 130-pound man to the same running speedspeed

• A baseball maybe accelerated faster than a shot A baseball maybe accelerated faster than a shot because of the difference in weightbecause of the difference in weight

• The force required to run at half speed is less than The force required to run at half speed is less than the force required to run at top speedthe force required to run at top speed

• To impart speed to a ball or an object, the body To impart speed to a ball or an object, the body part holding the object must be rapidly acceleratedpart holding the object must be rapidly accelerated

Page 36: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Law of Reaction• For every action there is an opposite and equal For every action there is an opposite and equal

reaction.reaction.– As we place force on a surface by walking over As we place force on a surface by walking over

it, the surface provides an equal resistance back it, the surface provides an equal resistance back in the opposite direction to the soles of our feetin the opposite direction to the soles of our feet

– Our feet push down & back, while the surface Our feet push down & back, while the surface pushes up & forwardpushes up & forward

• Force of the surface reacting to the force we Force of the surface reacting to the force we place on it is place on it is ground reaction forceground reaction force

Page 37: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Law of Reaction

• We provide the action force while We provide the action force while the surface provides the reaction the surface provides the reaction forceforce– easier to run on a hard track than on a easier to run on a hard track than on a

sandy beach due to the difference in the sandy beach due to the difference in the ground reaction forces of the two ground reaction forces of the two surfacessurfaces

– track resists the runner's propulsion track resists the runner's propulsion force, and the reaction drives the runner force, and the reaction drives the runner aheadahead

From Hamilton N, Luttgens K: Kinesiology: scientific basis of human motion, ed 10, 2002, McGraw-Hill.

Page 38: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Law of Reaction– sand dissipates the runner's force reducing the sand dissipates the runner's force reducing the

reaction force with the apparent loss in forward reaction force with the apparent loss in forward force & speedforce & speed

– sprinter applies a force in excess of 300 pounds sprinter applies a force in excess of 300 pounds on his starting blocks, which resist with an on his starting blocks, which resist with an equal forceequal force

– in flight, movement of one part of the body in flight, movement of one part of the body produces a reaction in another part because produces a reaction in another part because there is no resistive surface to supply a reaction there is no resistive surface to supply a reaction forceforce

Page 39: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Friction• FrictionFriction - force that results from the - force that results from the

resistance between surfaces of two objects resistance between surfaces of two objects from moving upon one anotherfrom moving upon one another– Depending increased or decreased friction may Depending increased or decreased friction may

be desiredbe desired– To run, we depend upon friction forces between To run, we depend upon friction forces between

our feet & the ground so that we may exert our feet & the ground so that we may exert force against the ground & propel ourselves force against the ground & propel ourselves forwardforward

Page 40: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Friction– With slick ground or shoe surface friction With slick ground or shoe surface friction

is reduced & we are more likely to slipis reduced & we are more likely to slip

– In skating, we desire decreased friction so In skating, we desire decreased friction so that we may slide across the ice with less that we may slide across the ice with less resistanceresistance

Page 41: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Friction• Static friction or kinetic frictionStatic friction or kinetic friction

– Static frictionStatic friction - the amount of friction between - the amount of friction between two objects that have not yet begun to movetwo objects that have not yet begun to move

– Kinetic friction Kinetic friction - friction occurring between two - friction occurring between two objects that are sliding upon one anotherobjects that are sliding upon one another

Page 42: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Friction• Static friction is always greater than kinetic Static friction is always greater than kinetic

frictionfriction– It is always more difficult to initiate dragging an It is always more difficult to initiate dragging an

object across a surface than to continue object across a surface than to continue draggingdragging

– Static friction may be increased by increasing Static friction may be increased by increasing the normal or perpendicular forces pressing the the normal or perpendicular forces pressing the two objects together such as in adding more two objects together such as in adding more weight to one object sitting on the other objectweight to one object sitting on the other object

Page 43: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Friction• To determine the amount of friction forces To determine the amount of friction forces

consider both forces pressing the two consider both forces pressing the two objects together & the objects together & the coefficient of frictioncoefficient of friction – depends upon the hardness & roughness of the depends upon the hardness & roughness of the

surface texturessurface textures

• Coefficient of friction - ratio between force Coefficient of friction - ratio between force needed to overcome the friction over the needed to overcome the friction over the force holding the surfaces togetherforce holding the surfaces together

Page 44: Biomechanical Factors &Concepts Chapter 3. Biomechanics:Biomechanics: –The study of mechanics as it relates to functional and anatomical analysis of biological

Friction• Rolling frictionRolling friction - resistance to an object - resistance to an object

rolling across a surface such as a ball rolling rolling across a surface such as a ball rolling across a court or a tire rolling across the across a court or a tire rolling across the groundground– Rolling friction is always much less that static Rolling friction is always much less that static

or kinetic frictionor kinetic friction

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Balance, equilibrium, & stability• BalanceBalance - ability to control equilibrium, - ability to control equilibrium,

either static or dynamiceither static or dynamic

• EquilibriumEquilibrium - state of zero acceleration - state of zero acceleration where there is no change in the speed or where there is no change in the speed or direction of the bodydirection of the body– static or dynamicstatic or dynamic

• Static equilibrium - Static equilibrium - body is at rest or body is at rest or completely motionlesscompletely motionless

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Balance, equilibrium, & stability• Dynamic equilibriumDynamic equilibrium - all applied & inertial - all applied & inertial

forces acting on the moving body are in forces acting on the moving body are in balance, resulting in movement with balance, resulting in movement with unchanging speed or directionunchanging speed or direction

• To control equilibrium & achieve balance, To control equilibrium & achieve balance, stabilitystability needs to be maximized needs to be maximized

• Stability is the resistance to a Stability is the resistance to a – change in the body's accelerationchange in the body's acceleration– disturbance of the body's equilibriumdisturbance of the body's equilibrium

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Balance, equilibrium, & stability• Stability is enhanced by determining body's Stability is enhanced by determining body's

center of gravitycenter of gravity & appropriately changing it & appropriately changing it• Center of gravity - point at which all of Center of gravity - point at which all of

body's mass & weight are equally balanced body's mass & weight are equally balanced or equally distributed in all directionsor equally distributed in all directions

• Balance - important in resting & moving Balance - important in resting & moving bodiesbodies

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Balance, equilibrium, & stability• Generally, balance is desiredGenerally, balance is desired• Some circumstances exist where movement Some circumstances exist where movement

is improved when the body tends to be is improved when the body tends to be unbalancedunbalanced

• General factors applicable to enhancing General factors applicable to enhancing equilibrium, maximizing stability, & equilibrium, maximizing stability, & ultimately achieving balance:ultimately achieving balance:1.1.  A person has balance when the center of gravity A person has balance when the center of gravity

falls within the base of supportfalls within the base of support

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Balance, equilibrium, & stability2.2.  A person has balance in the direct proportion to A person has balance in the direct proportion to

the size of the basethe size of the baseThe larger the base of support, the more balanceThe larger the base of support, the more balance

3.3.  A person has balance depending on the weight A person has balance depending on the weight (mass)(mass)The greater the weight, the more balanceThe greater the weight, the more balance

4. A person has balance, depending on the height 4. A person has balance, depending on the height of the center of gravityof the center of gravityThe lower the center of gravity, the more balanceThe lower the center of gravity, the more balance

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Balance, equilibrium, & stability5. A person has balance, depending on where the 5. A person has balance, depending on where the

center of gravity is in relation to the base of center of gravity is in relation to the base of supportsupportBalance is less if the center of gravity is near the Balance is less if the center of gravity is near the edge of the baseedge of the baseWhen anticipating an oncoming force, stability When anticipating an oncoming force, stability may be improved by placing the center of gravity may be improved by placing the center of gravity nearer the side of the base of support expected to nearer the side of the base of support expected to receive the forcereceive the force

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Balance, equilibrium, & stability6. In anticipation of an oncoming force, stability 6. In anticipation of an oncoming force, stability

may be increased by enlarging the size of the may be increased by enlarging the size of the base of support in the direction of the anticipated base of support in the direction of the anticipated force.force.

7. Equilibrium may be enhanced by increasing the 7. Equilibrium may be enhanced by increasing the friction between the body & the surfaces it friction between the body & the surfaces it contactscontacts

8. Rotation about an axis aids balance8. Rotation about an axis aids balanceA moving bike is easier to balance than a A moving bike is easier to balance than a stationary bikestationary bike

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Balance, equilibrium, & stability9. Kinesthetic physiological functions contribute to 9. Kinesthetic physiological functions contribute to

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

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Balance, equilibrium, & stability• In walking a person throws the body in and In walking a person throws the body in and

out of balance with each stepout of balance with each step• In rapid running movements where moving In rapid running movements where moving

inertia is high, the center of gravity has to be inertia is high, the center of gravity has to be lowered to maintain balance when stopping lowered to maintain balance when stopping or changing directionor changing direction

• In jumping activities the center of gravity In jumping activities the center of gravity needs to be raised as high as possibleneeds to be raised as high as possible

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Force• Muscles are the main source of force that Muscles are the main source of force that

produces or changes movement of a body produces or changes movement of a body segment, the entire body, or some object segment, the entire body, or some object thrown, struck, or stoppedthrown, struck, or stopped

• Strong muscles are able to produce more Strong muscles are able to produce more force than weak musclesforce than weak muscles– both maximum and sustained exertion over a both maximum and sustained exertion over a

period of timeperiod of time

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Force• ForcesForces either push or pull on an object in an either push or pull on an object in an

attempt to affect motion or shapeattempt to affect motion or shape

• Without forces acting on an object there Without forces acting on an object there would be no motionwould be no motion

• Force - product of mass times accelerationForce - product of mass times acceleration

• Mass - amount of matter in a bodyMass - amount of matter in a body

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Force• The weight of a body segment or the entire The weight of a body segment or the entire

body X the speed of acceleration determines body X the speed of acceleration determines the forcethe force– Important in footballImportant in football– Also important in activities using only a part of Also important in activities using only a part of

the bodythe body– In throwing a ball, the force applied to the ball is In throwing a ball, the force applied to the ball is

equal to the weight of the arm times the speed of equal to the weight of the arm times the speed of acceleration of the armacceleration of the arm

– Leverage factors are also importantLeverage factors are also important

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ForceForce = mass x accelerationForce = mass x acceleration

F = M x AF = M x A

• Momentum (Momentum (quantity of motion) - equal to quantity of motion) - equal to mass times velocitymass times velocity

• The greater the momentum, the greater the The greater the momentum, the greater the resistance to change in the inertia or state of resistance to change in the inertia or state of motionmotion

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Force• Many activities, particularly upper extremity, Many activities, particularly upper extremity,

require a summation of forces from the require a summation of forces from the beginning of movement in the lower segment beginning of movement in the lower segment of the body to the twisting of the trunk and of the body to the twisting of the trunk and movement at the shoulder, elbow, and wrist movement at the shoulder, elbow, and wrist jointsjoints

• Ex. golf drive, shot-putting, discus and Ex. golf drive, shot-putting, discus and javelin throwingjavelin throwing

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Mechanical loading basics• Significant mechanical loads are generated & Significant mechanical loads are generated &

absorbed by the tissues of the bodyabsorbed by the tissues of the body• Internal or external forces may causing these Internal or external forces may causing these

loadsloads• Only muscles can actively generate internal Only muscles can actively generate internal

force, but tension in tendons, connective force, but tension in tendons, connective tissues, ligaments, and joints capsules may tissues, ligaments, and joints capsules may generate passive internal forcesgenerate passive internal forces

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Mechanical loading basics• External forces are produced from outside External forces are produced from outside

the body & originate from gravity, inertia, or the body & originate from gravity, inertia, or direct contactdirect contact

• All tissues, in varying degrees, resist changes All tissues, in varying degrees, resist changes in their shapein their shape

• Tissue deformation may result from external Tissue deformation may result from external forces, but can result from internally forces, but can result from internally generated forcesgenerated forces

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Mechanical loading basics• Internal forces canInternal forces can

– fracture bonesfracture bones– dislocate jointsdislocate joints– disrupt muscles & connective tissuesdisrupt muscles & connective tissues

• To prevent injury or damage from tissue To prevent injury or damage from tissue deformation the body must be used to absorb deformation the body must be used to absorb energy from both internal & external forcesenergy from both internal & external forces

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Mechanical loading basics• It is advantageous to absorb force over larger It is advantageous to absorb force over larger

aspects of our body rather than smaller and to aspects of our body rather than smaller and to spread the absorption rate over a greater spread the absorption rate over a greater period of timeperiod of time

• Stronger & healthier tissues are more likely Stronger & healthier tissues are more likely to withstand excessive mechanical loading & to withstand excessive mechanical loading & the resultant excessive tissue deformationthe resultant excessive tissue deformation

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Mechanical loading basics• Excessive tissue deformation due to Excessive tissue deformation due to

mechanical loading may result frommechanical loading may result from– Tension (stretching or strain)Tension (stretching or strain)– CompressionCompression– ShearShear– BendingBending– Torsion (twisting)Torsion (twisting)

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Throwing• In the performance of various sport skills In the performance of various sport skills

such as throwing, many applications of the such as throwing, many applications of the laws of leverage, motion, and balance may be laws of leverage, motion, and balance may be found found

• In throwing, the angular motion of the levers In throwing, the angular motion of the levers (bones) of the body (trunk, shoulder, elbow, (bones) of the body (trunk, shoulder, elbow, and wrist) is used to give linear motion to the and wrist) is used to give linear motion to the ball when it is releasedball when it is released

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Throwing• In throwing, the individual's inertia & the In throwing, the individual's inertia & the

ball's inertia must be overcome by the ball's inertia must be overcome by the application of forceapplication of force (Law of inertia) (Law of inertia)

• Muscles of the body provide the force to Muscles of the body provide the force to move the body parts & the ball move the body parts & the ball

• Law of accelerationLaw of acceleration is in effect with the is in effect with the muscular force necessary to accelerate the muscular force necessary to accelerate the arm, wrist, & handarm, wrist, & hand

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Throwing• The greater the force (mass X acceleration) The greater the force (mass X acceleration)

that a person can produce, the faster the arm that a person can produce, the faster the arm will move, and thus the greater the speed that will move, and thus the greater the speed that will be imparted to the ballwill be imparted to the ball

• The reaction of the feet against the surface on The reaction of the feet against the surface on which the subject stands applies the which the subject stands applies the law of law of reactionreaction

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Throwing• The longer the lever, the greater the speed The longer the lever, the greater the speed

that can be imparted to thethat can be imparted to the ball ball– The body from the feet to the fingers can be The body from the feet to the fingers can be

considered as one long leverconsidered as one long lever– The longer the lever, from natural body length or The longer the lever, from natural body length or

the body movements to the extended backward the body movements to the extended backward position, the greater will be the arc through position, the greater will be the arc through which it accelerates and thus the greater the which it accelerates and thus the greater the speed imparted to the thrown objectspeed imparted to the thrown object

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Throwing• Short levers are advantageous in taking less total Short levers are advantageous in taking less total

time to release the balltime to release the ball• Balance or equilibrium is a factor in throwing when Balance or equilibrium is a factor in throwing when

the body is rotated posteriorly in the beginning of the body is rotated posteriorly in the beginning of the throwthe throw– the body is moved nearly out of balance to the rear,the body is moved nearly out of balance to the rear,

– balance changes again with the forward movementbalance changes again with the forward movement

– balance is reestablished with the follow-through when the balance is reestablished with the follow-through when the feet are spread and the knees & trunk are flexed to lower feet are spread and the knees & trunk are flexed to lower the center of gravity the center of gravity

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Web SitesBiomechanics: The Magazine of Body Movement and Medicine

www.biomech.com/ COSI Hands-on science centers

www.cosi.org/onlineExhibits/simpMach/sm1.swf– A Flash site demonstrating simple machine explanations

Edquestwww.edquest.ca/pdf/sia84notes.pdf – Text, pictures, and illustrations on simple and complex machines

GRD Training Corporationwww.physchem.co.za/Motion/Motion%20Index.htm– Explanations of physics principles for in motion with quizzes

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Web SitesIntegrated Publishing

www.tpub.com/content/engine/14037/index.htm– Engine mechanics

International Society of Biomechanicswww.isbweb.org/ – Software, data, information, resources, yellow pages, conferences.

James Madison Memorial High Schoolwww.madison.k12.wi.us/jmm/isp/U7PDF08.pdf– A pdf file explaining the six types of simple machines

Kinesiology Biomechanics Classeswww.uoregon.edu/~karduna/biomechanics/kinesiology.htm – A listing of numerous biomechanics and kinesiology class site on

the web with many downloadable presentations and notes

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Web SitesOptusnet.com

www.members.optusnet.com.au/ncrick/converters/moment.html– Conversion formulas for physics variables

The Physics Classroomwww.glenbrook.k12.il.us/gbssci/phys/Class/BBoard.html– Numerous topics including the laws of motion and other physics

principlesPhysics Concepts—Simple Machines

www.ceeo.tufts.edu/robolabatceeo/K12/classroom/lever.asp – An overview of physics concepts involved in the study of

biomechanics.

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Web SitesSports Coach—Levers

www.brianmac.demon.co.uk/levers.htm – A basic review of levers with excellent links to the study of muscle

training & function.Worsley School

www.wcsscience.com/simple/machines.html– Detailed explanations and illustrations on simple machines