IMPORTANT TERMINOLOGIES

1. Kinematics and Kinetic BasicKinematics and Kinetic Basic
ConceptsConcepts
Lecture-2Lecture-2
Saifullah KhalidSaifullah Khalid
LecturerLecturer
School of Physiotherapy,School of Physiotherapy,
IPM&R, Dow University of Health Science, KarachiIPM&R, Dow University of Health Science, Karachi
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2. MassMass
““ The quantity of matterThe quantity of matter
in an objectin an object ””
No variation in massNo variation in mass
with regard to location orwith regard to location or
gravitational conditionsgravitational conditions
““It represents theIt represents the
resistance to a change ofresistance to a change of
state of an objectstate of an object””
WeightWeight
““ The force that resultsThe force that results
from the action of afrom the action of a
gravitational field on agravitational field on a
massmass ””
Units:Units: Newton, PoundNewton, Pound
force (lbf)force (lbf)
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3. InertiaInertia
 ““ The resistance to a change of state duringThe resistance to a change of state during
rotationrotation ””
I = m × rI = m × r ²²
Units:Units: kilogram meter squaredkilogram meter squared ((kg×mkg×m²²)), Slug inch, Slug inch
squaredsquared (sl×in(sl×in²)²)
The Truck and Ladder
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4. Linear MotionLinear Motion
 ““ Motion in which allMotion in which all
parts of the body travelparts of the body travel
along parallel pathsalong parallel paths ””
 Also calledAlso called TranslationTranslation
 Rectilinear translationRectilinear translation
 Curvilinear translationCurvilinear translation
Angular MotionAngular Motion
 ““ Motion in which allMotion in which all
particles in the bodyparticles in the body
travel in a circulartravel in a circular
mannermanner,, if the axis ofif the axis of
rotation is fixedrotation is fixed ””
 If theIf the axis of rotation isaxis of rotation is
not fixednot fixed the motion isthe motion is
actually aactually a combination ofcombination of
translationtranslation && rotationrotation
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5. DisplacementDisplacement
 ““ The change in the position of aThe change in the position of a
body”body”
 TranslationalTranslational
 Rotational changeRotational change
 CombinedCombined
 Translational changeTranslational change
 Example:Example: General movement of theGeneral movement of the
human bodyhuman body
 Rotational changeRotational change
 Example:Example: Motion of limbsMotion of limbs
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6. VelocityVelocity
 ““The rate at which anThe rate at which an
object changes itsobject changes its
position”position”
 AngularAngular && LinearLinear
VelocityVelocity
 HorizontalHorizontal &&VerticalVertical
VelocityVelocity
SpeedSpeed
 "How fast an object is"How fast an object is
moving”moving”
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7. Linear velocityLinear velocity
 ““ The rate at which aThe rate at which a
body moves in abody moves in a
straight linestraight line ””
 Units:Units:
 Meters/second (Meters/second (m/sm/s))
 Feet/second (Feet/second (ft/secft/sec oror
ft/sft/s), Miles per hour), Miles per hour
((mphmph))
Angular VelocityAngular Velocity
 ““ The rate of changeThe rate of change
of angularof angular
displacement withdisplacement with
respect to timerespect to time ””
 Units:Units:
 Radians/secRadians/sec ( rad/s )( rad/s )
 degrees/secdegrees/sec (deg/sec(deg/sec
oror ° /sec° /sec oror ° /s° /s ))
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8. AccelerationAcceleration
 “The rate of change ofThe rate of change of
velocity with respect tovelocity with respect to
timetime”
 PositivePositive,, NegativeNegative,, ZeroZero
valuesvalues
 DecelerationDeceleration (Negative(Negative
acceleration)acceleration)
 Units:Units:
 (m/s(m/s²²), (ft/sec), (ft/sec² or² or ft/sft/s²²),),
(in/sec(in/sec²² or in/sor in/s²²))
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9. Forces & MomentsForces & Moments
Forces:Forces:
““A push or pull" that results fromA push or pull" that results from
physical contact between two objectsphysical contact between two objects
Common examples Force:Common examples Force:
 Muscles/tendons pull, ligaments pull,Muscles/tendons pull, ligaments pull,
friction, ground reaction, weight, jointfriction, ground reaction, weight, joint
forces and joint reaction forcesforces and joint reaction forces
 Gravity is the only exceptionGravity is the only exception
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10. Force & MomentsForce & Moments
 Forces from the abd. & add. musclesForces from the abd. & add. muscles
act through their tendons, while theact through their tendons, while the
hip joint reaction forcehip joint reaction force acts throughacts through
its respective joint CORits respective joint COR
 In general, the point of application ofIn general, the point of application of
a force is located with respect to aa force is located with respect to a
fixed point on a body, usually thefixed point on a body, usually the
joint CORjoint COR
 This information is usedThis information is used to calculateto calculate
thethe momentmoment due to that forcedue to that force
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11. Force & MomentsForce & Moments
Moment ...Moment ...
 The bending action of forceThe bending action of force
 In biomechanics, a momentIn biomechanics, a moment
(M)(M) is typicallyis typically caused by acaused by a
force acting at a distanceforce acting at a distance (r)(r)
from the COR of a segmentfrom the COR of a segment
M = rM = r ××FF
 A moment tends to cause aA moment tends to cause a
rotationrotation
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12. Moments & Moment ArmMoments & Moment Arm
Torque …Torque …
 Synonymous with a momentSynonymous with a moment
 Effect of a force that tendsEffect of a force that tends
to cause rotation about anto cause rotation about an
axisaxis
 Moment Arm …Moment Arm …
 ““The distance that isThe distance that is
perpendicularperpendicular
to the force vector”to the force vector”
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13. Force CoupleForce Couple
 ““ An arrangement of twoAn arrangement of two
equal and opposite parallelequal and opposite parallel
forces that tend to causeforces that tend to cause
rotationrotation ””
 Pure examples are rare inPure examples are rare in
musculoskeletal systemmusculoskeletal system
 In general, muscles areIn general, muscles are
responsible for producingresponsible for producing
both forcesboth forces andand momentsmoments,,
thus resulting in boththus resulting in both
translationaltranslational andand rotationalrotational
motionmotion09/29/1609/29/16 1313

14. Muscle ForcesMuscle Forces
 Three important parameters to consider theThree important parameters to consider the
force of a muscle;force of a muscle;
 OrientationOrientation,, MagnitudeMagnitude andand Point ofPoint of
applicationapplication
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15. Clinical RelevanceClinical Relevance
 Muscles generate 2 types of forcesMuscles generate 2 types of forces
 Angular MotionAngular Motion ((RotationRotation))
 Linear MotionLinear Motion ((TranslationTranslation) may) may
bebe StabilizingStabilizing oror destabilizing forcedestabilizing force
 ExampleExample ……
 Supraspinatus orientation & action …Supraspinatus orientation & action …
 Stabilize head of humrus intoStabilize head of humrus into
glenoid cavityglenoid cavity
 Deltoid orientationDeltoid orientation & action …& action …
 Produces aProduces a destabilizing forcedestabilizing force thatthat
may result inmay result in superior translationsuperior translation ofof
the humeral headthe humeral head
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16. FrictionFriction
 “ The tangential force acting
between two bodies in contact that
opposes motion or impending
motion ”
 Static FrictionStatic Friction
 Kinetic FrictionKinetic Friction
 Coulomb FrictionCoulomb Friction
 Friction b/w dry surfacesFriction b/w dry surfaces
 Most biomechanical analysesMost biomechanical analyses
involve dry frictioninvolve dry friction
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17. Joint ForcesJoint Forces
 ““ The forces that exist betweenThe forces that exist between
the Articular surfaces of thethe Articular surfaces of the
jointjoint ””
 Joint forces are the result ofJoint forces are the result of
muscle forces, gravity, andmuscle forces, gravity, and
inertial forcesinertial forces ((usually, muscleusually, muscle
forces are responsible for theforces are responsible for the
largest partlargest part))
 Also called Bone on bone forcesAlso called Bone on bone forces
((not joint reaction forcesnot joint reaction forces))
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18. Joint Reaction ForcesJoint Reaction Forces
 “ The equal and opposite forces that
exist between adjacent bones at a
joint caused by the weight and
inertial forces of the two segments ””
 A fairlyA fairly abstract conceptabstract concept useful inuseful in
mathematical analysis but not muchmathematical analysis but not much
use in practiceuse in practice
 Must not be confused with jointMust not be confused with joint
forcesforces that include the effects ofthat include the effects of
muscle actionmuscle action
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19. Ground Reaction ForcesGround Reaction Forces
 “ The forces that act on the
body as a result of interaction
with the ground ”
 According to Newton’s thirdAccording to Newton’s third
law …law …
““Ground reaction forces areGround reaction forces are
equal and opposite to thoseequal and opposite to those
that the body is applying tothat the body is applying to
the ground”the ground”
 Ground reaction forces can beGround reaction forces can be
measuredmeasured with awith a forceforce
platformplatform
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20. Center of PressureCenter of Pressure
 ““ Center of pressure is the pointCenter of pressure is the point
on a body where the total sum ofon a body where the total sum of
the pressure field acts,the pressure field acts, causing acausing a
force to act through that pointforce to act through that point
 Generally, the force is appliedGenerally, the force is applied
over a diffuse areaover a diffuse area e.g. the plantare.g. the plantar
aspect of the footaspect of the foot
 During Standing …During Standing …
When pressure exists under bothWhen pressure exists under both
heels and balls of the foot, theheels and balls of the foot, the
COPCOP will be in thewill be in the mid-footmid-foot
RegionRegion
 During Walking …During Walking …
COPCOP moves under the footmoves under the foot
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21. Free Body DiagramFree Body Diagram
 ““ A diagram in which all theA diagram in which all the
forces and torques acting on aforces and torques acting on a
body are identifiedbody are identified ””
 This includes forces likeThis includes forces like gravitygravity,,
frictional forcesfrictional forces, and, and reactionreaction
forcesforces caused by contact withcaused by contact with
other objectsother objects
 The name originates from theThe name originates from the
fact that the body is “fact that the body is “ freedfreed ””
from its external contacts that arefrom its external contacts that are
replaced by reaction forcesreplaced by reaction forces
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22. F is the force applied to the hand by the
handle of the cable attached to the weight
in the weight pan,
W is the total weight of the lower arm
acting at the center of gravity of the lower
arm,
FM1 is the force exerted by the biceps on
the radius,
FM3 is the force exerted by the
brachioradialis muscles on the radius,
FM2 is the force exerted by the brachialis
muscles on the ulna, and
FJ is the resultant reaction force at the
humeroulnar and humeroradial joints of the
elbow.
Example of free body diagram
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23. Newton’s LawsNewton’s Laws
 Sir Isaac NewtonSir Isaac Newton (1642-1727)(1642-1727)
 IN-MO-REIN-MO-RE
 First Newton’s lawFirst Newton’s law (Law of(Law of InInertia)ertia)
 Second Newton’s lawSecond Newton’s law (Law of(Law of
MoMomentum)mentum)
 Third Newton’s lawThird Newton’s law (Law of(Law of
ReReaction)action)
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24. Newton’s LawsNewton’s Laws
 First law …First law …
 ““ An object remains at rest or constant velocity unlessAn object remains at rest or constant velocity unless
acted upon by an unbalanced external forceacted upon by an unbalanced external force ””
 Second law …Second law …
 ““ If there is an unbalanced force acting on a object, itIf there is an unbalanced force acting on a object, it
produces an acceleration in the direction of the force,produces an acceleration in the direction of the force,
directly proportional to the forcedirectly proportional to the force (f = ma)(f = ma)””
 Third law ……Third law ……
 ““ For every action (For every action (forceforce) there is a reaction () there is a reaction (opposingopposing
forceforce) of equal magnitude but in opposite direction) of equal magnitude but in opposite direction ””
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25. Newton’s LawsNewton’s Laws
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26. Modes of DeformationModes of Deformation
 When an object (in static equilibrium) isWhen an object (in static equilibrium) is
subjected to external force, there is somesubjected to external force, there is some
local shape change within the object calledlocal shape change within the object called
deformationdeformation
 External forces may beExternal forces may be
Normal forcesNormal forces i.e. tensile or compressivei.e. tensile or compressive
forcesforces
ShearShear i.e. tangential forcesi.e. tangential forces
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27. Normal and shear stressesNormal and shear stresses
 Normal stress..Normal stress..
The internal force that isThe internal force that is
opposite in the direction ofopposite in the direction of
externally applied forceexternally applied force
and parallel to the long axisand parallel to the long axis
of material or perpendicularof material or perpendicular
to its cross sectionto its cross section
It may be tensile stress orIt may be tensile stress or
compressive stresscompressive stress
Represented byRepresented by σσ=F/A=F/A09/29/1609/29/16 2727

28. Shear stressesShear stresses
 The intensity of internalThe intensity of internal
force that is opposite in theforce that is opposite in the
direction of external load butdirection of external load but
perpendicular to the longperpendicular to the long
axis of material or coplanaraxis of material or coplanar
with its cross sectionwith its cross section
Represented byRepresented by ττ= F/A= F/A
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29. Normal and Shear StrainsNormal and Shear Strains
 Strain…Strain…
 Measure of the degree of deformationMeasure of the degree of deformation
 Normal strainNormal strain….….
The ratio of the change (increase orThe ratio of the change (increase or
decrease) in length to the originaldecrease) in length to the original
(undeformed) length(undeformed) length
Tensile or +ive strainTensile or +ive strain
Compressive or –ive strainCompressive or –ive strain
 Denoted byDenoted by εε==ΔΔl/ll/l
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30. Shear strainShear strain
 Related to distortions caused by shearRelated to distortions caused by shear
stressesstresses
 Denoted with the symbolDenoted with the symbol γ =γ = d/h.d/h.
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31. STRESS-STRAIN DIAGRAMSSTRESS-STRAIN DIAGRAMS
 Different materials mayDifferent materials may
demonstrate differentdemonstrate different
stress strain relationshipsstress strain relationships
 Consider the stress-strainConsider the stress-strain
diagram showndiagram shown
 Labeled as O, P, E, Y, U &Labeled as O, P, E, Y, U &
RR
 Type of material,Type of material,
temperature and load ratetemperature and load rate
can alter s-s relationshipcan alter s-s relationship
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32. ELASTIC AND PLASTICELASTIC AND PLASTIC
DEFORMATIONSDEFORMATIONS
 Elasticity is defined as the ability of aElasticity is defined as the ability of a
material to resume its original (stress-free)material to resume its original (stress-free)
size and shape on removal of applied loadssize and shape on removal of applied loads
 An elastic material whose stress-strainAn elastic material whose stress-strain
diagram is a straight line is called a linearlydiagram is a straight line is called a linearly
elastic material.elastic material.
 For such a material, the stress is linearlyFor such a material, the stress is linearly
proportional to strainproportional to strain

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33.  The slope of the stress-strainThe slope of the stress-strain
diagram in the elastic regiondiagram in the elastic region
is called the elastic oris called the elastic or
Young’s modulus of theYoung’s modulus of the
material,material,
 denoted by E. sodenoted by E. so σσ= Eε.= Eε.
 Plasticity implies permanentPlasticity implies permanent
deformations. Materials maydeformations. Materials may
undergo plastic deformationsundergo plastic deformations
following elasticfollowing elastic
deformations when they aredeformations when they are
loaded beyond their elasticloaded beyond their elastic
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34. VISCOELASTICITYVISCOELASTICITY
 Tissues in which the physical propertiesTissues in which the physical properties
associated with the stress-strain curveassociated with the stress-strain curve
change(strain) as a function of time arechange(strain) as a function of time are
consideredconsidered viscoelasticviscoelastic
 Most tissues within the musculoskeletalMost tissues within the musculoskeletal
system demonstrate at least some degreesystem demonstrate at least some degree
of Viscoelasticityof Viscoelasticity
 The stress-strain curve of a viscoelasticThe stress-strain curve of a viscoelastic
material is also sensitive to thematerial is also sensitive to the rate ofrate of
loading of the tissueloading of the tissue
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35.  In general, theIn general, the slope of aslope of a
stress-strain relationshipstress-strain relationship
when placed underwhen placed under
tension or compressiontension or compression
increases throughout itsincreases throughout its
elastic range as the rateelastic range as the rate
of the loading increasesof the loading increases
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36. Creep phenomenonCreep phenomenon
 One phenomenon of aOne phenomenon of a
viscoelastic material isviscoelastic material is
creepcreep
 creep describes acreep describes a
progressive strain of aprogressive strain of a
material when exposedmaterial when exposed toto
a constant load over timea constant load over time
 if the stress is heldif the stress is held
constant, the strainconstant, the strain
increases with timeincreases with time09/29/1609/29/16 3636

37. Stress relaxation phenomenonStress relaxation phenomenon
 Strain is maintainedStrain is maintained
at a constant levelat a constant level
 while observing thewhile observing the
stress response ofstress response of
the material.the material.
 the stress decreasesthe stress decreases
with time (relaxation)with time (relaxation)
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38. Center of Gravity and StabilityCenter of Gravity and Stability
 COGCOG ::
 ““The point at which all of the weight of that body to beThe point at which all of the weight of that body to be
concentrated”concentrated”
 It changes on a body's shape and body mass distributionIt changes on a body's shape and body mass distribution
changeschanges
 COGCOG in anatomical position …in anatomical position … approx. at the level ofapprox. at the level of
22ndnd
sacral vertebrasacral vertebra
 Importance of the location of a person’s COGImportance of the location of a person’s COG ……
 Important in athletics and other fast motionsImportant in athletics and other fast motions
 More important clinically i.e. for motions in which theMore important clinically i.e. for motions in which the
acceleration is negligible, COG must be containedacceleration is negligible, COG must be contained
within a person's base of support to maintain stabilitywithin a person's base of support to maintain stability
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39. Center of Gravity and StabilityCenter of Gravity and Stability
 When a person stands upright,When a person stands upright,
his COG is post. to his toes, sohis COG is post. to his toes, so
there is a counterclockwisethere is a counterclockwise
moment at his toes. This is amoment at his toes. This is a
stable positionstable position
As the person bends forward,As the person bends forward,
his COG moves anterior to hishis COG moves anterior to his
toes and the weight of his uppertoes and the weight of his upper
body produces a clockwisebody produces a clockwise
moment at his toes. Since theremoment at his toes. Since there
is no further anterior support,is no further anterior support,
this moment is unbalanced andthis moment is unbalanced and
the man will fall forwardthe man will fall forward09/29/1609/29/16 3939

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