© 2008 McGraw-Hill Higher Education. All Rights Reserved. Chapter 11: The Description of Human Motion KINESIOLOGY Scientific Basis of Human Motion, 11

© 2008 McGraw-Hill Higher Education. All Rights Reserved.

Chapter 11:The Description of

Human Motion

KINESIOLOGY

Scientific Basis of Human Motion, 11th edition

Hamilton, Weimar & LuttgensPresentation Created by

TK Koesterer, Ph.D., ATC

Humboldt State University

Revised by Hamilton & Weimar

KINESIOLOGY

Scientific Basis of Human Motion, 11th edition

Hamilton, Weimar & LuttgensPresentation Created by

TK Koesterer, Ph.D., ATC

Humboldt State University

Revised by Hamilton & Weimar


Objectives1. Name the motions experienced by the human body,

and describe the factors that cause & modify motion.

2. Name & properly use terms that describe linear & rotary motion.

3. Explain the interrelationship that exist among displacement, velocity, & acceleration, & use them to describe & analyze human motion.

4. Describe behavior of projectiles, & explain how angle, speed, & height of projection affect that behavior.

5. Describe relationship between linear & rotary movement, & explain significance to human motion.

6. Identify kinematic components used to describe skillful performance of a motor task .


Relative Motion

• Motion is the act or process of changing place or position with respect to some reference object.

• At rest or in motion depends totally on the reference.

• Sleeping passenger in a flying plane:– At rest in reference to the plane.– In motion in reference to the earth.


Cause of Motion

• The cause of motion is a form of force.• Force is the instigator of movement.• Force must be sufficiently great to overcome

the object’s inertia, or resistance to motion.• Force relative to resistance will determine if

the object will move or remain at rest.


Kinds of Motion

• Although the variety of ways in which objects move appears to be almost limitless, careful consideration reveals only two classifications of movement patterns:– Translatory or linear– Rotary or angular


Translatory Movement

• An object is translated as a whole from one location to another.– Rectilinear: straight-line progression– Curvilinear: curved translatory movement

Fig 11.1

Rectilinear Rectilinear motionmotion

Fig 11.2

CurvilinearCurvilinearmotionmotion


Circular Motion

• A special form of curvilinear motion.• Object moves along the circumference of a

circle, a curved path of constant radius.• The logic relates to the fact that an unbalanced

force acts on the object to keep it in a circle .• If force stops acting on the object, it will move in

a linear path tangent to the direction of movement when released.


Rotary, or Angular, Motion

• Typical of levers, wheels, & axles

• Object acting as a radius moves about a fixed point.

• Measured as an angle, in degrees.

• Body parts move in an arc about a fixed point.

Fig 11.3


Rotary, or Angular, Motion

• Circular motion describes motion of any point on the radius.

• Angular motion is descriptive of motion of the entire radius.

• When a ball is held as the arm moves in a windmill fashion– ball is moving with circular motion.– arm acts as a radius moving with angular

motion.


Other Movement Patterns

• Combination of rotary & translatory is called general motion

• Angular motions of forearm, upper arm & legs.• Hand travels linearly and imparts linear force to

the foil

Fig 11.4


Kinds of Motion Experience by the Body

• Most joints are axial.• Segments undergo

primarily angular motion.

• Slight translatory motion in gliding joints.

Fig 11.5


Kinds of Motion Experience by the Body• Rectilinear movement when the body

is acted on by the force of gravity or a linear external force

Fig 11.7 Fig 11.6


Kinds of Motion Experience by the Body

• General motion – e.g. forward and backward rolls on ground

• Rotary motion – e.g. spinning on ice skates

• Curvilinear translatory motion – e.g. diving and jumping

• Reciprocating motion – e.g. swinging on a swing


Factors that Determine the Kind of Motion

• Depends primarily on the kind of motion permitted in a particular object.– Lever permits only angular motion.– Pendulum permits only oscillatory motion.

• If an object is freely movable, it permits either translatory or rotary motion.– Determined by where force is applied in

reference to its center of gravity.– Presence or absence of modifying forces.


Factors Modifying Motion

• External factors– Friction helps a runner gain traction, but

hinders the rolling of a ball.– Air resistance or wind is indispensable to

the sailboat’s motion, but may impede a runner.

– Water resistance is essential for propulsion, yet it hinders an objects’ progress through the water.


Factors Modifying Motion

• Internal or anatomical factors: – friction in joints; tension of antagonists,

ligaments & fasciae; anomalies of bone & joint structure; atmospheric pressure inside joints; and presence of interfering soft tissues.

• One of the major problems in movement is– How to take advantage of these factors.– How to minimize them when they are

detrimental to the movement.


KINEMATIC DESCRIPTION OF MOTION

Linear Kinematics • Distance

– How far an object has moved or traveled.• Displacement

– Distance an object has moved from a reference point.

– May not indicate how far object traveled.– A vector quantity having both magnitude

and direction.


Linear Kinematics • Walk north 3 km, then east 4 km.• What is the distance traveled?• What is the displacement?

Fig 11.8


Speed and Velocity

• Speed is how fast an object is moving, nothing about the direction of movement.– a scalar quantity

Average Speed = distance traveled or d

time t


• Velocity involves direction as well as speed– speed in a given direction– rate of displacement– a vector quantity

Average Velocity = displacement or s / t

time

v = s / t

Speed and Velocity


Acceleration

• The rate of change in velocity.• May be positive or negative.• If acceleration is positive then velocity will

increase.• If acceleration is negative then velocity will

decrease.

Average acceleration = final velocity – initial velocitytime

a = (vf – vi)/t


Acceleration

Fig 11.10

Section a:

v- increasing (+)

a-constant (+)

Section b:

v- constant (+)

a-zero

Section c:

v- non-linear increase (+)

a- non-constant (+)

Section d:

v- decreasing (+)

a- constant (-)


Acceleration Units

a = (final velocity – initial velocity) / time

a = (final m/sec – initial m/sec) / sec

a = (m/sec) / sec

a = m/sec2


Uniformly Accelerated Motion

• Constant acceleration rate.• Common with freely falling objects.• Air resistance is neglected.• Objects will accelerate at a uniform rate due

to acceleration of gravity.• Object projected upward will be slowed at the

same uniform rate due to gravity.


Acceleration of Gravity

• 32 ft/sec2 or 9.8 m/sec2

• Velocity will increase 9.8 m/sec every second when an object is dropped from some height. – End of 1 sec = 9.8 m/sec– End of 2 sec = 19.6 m/sec– End of 3 sec = 29.4 m/sec

• Does not consider resistance or friction of air.


Air Resistance

• Lighter objects will be affected more:– may stop accelerating (feather) and fall at

a constant rate.• Denser, heavier objects are affected less.• Terminal velocity – air resistance is increased

to equal accelerating force of gravity. – Object no longer accelerating, velocity

stays constant.– Sky diver = approximately 120 mph or

53 m/sec.


Laws of Uniformly Accelerated Motion

• Distance traveled & downward velocity can be determined for any point in time:

vf = vi + at

s = vi t + /2at2

vf 2 = vi 2 + 2as

Where:vf = final velocity

vi = initial velocity

a = accelerationt = times = displacement


Laws of Uniformly Accelerated Motion

• Time it takes for an object to rise to the highest point of its trajectory is equal to the time it takes to fall to its starting point.

• Upward flight is a mirror image of the downward flight.

• Release & landing velocities are equal, but opposite.

• Upwards velocities are positive.• Downward velocities are negative.


Projectiles

• Objects given an initial velocity and released.• Gravity is the only influence after release.* • Maximum horizontal displacement

– e.g. long jumper, shot-putter• Maximum vertical displacement

– e.g. high jumper, pole vault• Maximum accuracy

– e.g. shooting in basketball or soccer* Neglecting air resistance.


Projectiles

• Follows a predictable path, a parabola.

• Gravity will– slow upward motion.– increase downward

motion.– at 9.8 m/sec2

Fig 11.11


ProjectilesUpward portion

Position versus TimeUpward

0

1

2

3

4

5

6

0 0.2 0.4 0.6 0.8 1 1.2

Time (sec)

Pos

ition

y-d

irect

ion

(m)

Velocity versus TimeUpward

0

2

4

6

8

10

0 0.2 0.4 0.6 0.8 1 1.2

Time (sec)

Vel

ocity

y-d

irect

ion

(m/s

)

Acceleration versus TimeUpward

-12

-10

-8

-6

-4

-2

0

0 0.2 0.4 0.6 0.8 1 1.2

Time (sec)

Acc

eler

atio

n y-

dire

ctio

n (m

/s2)


ProjectilesDownward portion

Position versus TimeDownward

0

1

2

3

4

5

6

0 0.2 0.4 0.6 0.8 1 1.2

Time (sec)

Pos

ition

y-d

irect

ion

(m)

Velocity versus TimeDownward

-10

-8

-6

-4

-2

0

0 0.2 0.4 0.6 0.8 1 1.2

Time (sec)

Vel

ocity

y-d

irect

ion

(m/s

)

Acceleration versus TimeDownward

-12

-10

-8

-6

-4

-2

0

0 0.2 0.4 0.6 0.8 1 1.2

Time (sec)

Acc

eler

atio

n y-

dire

ctio

n (m

/s2)


Projectiles• Initial velocity at an angle of projection:

– Components• Vertical velocity: affected by gravity• Horizontal velocity: not affected by gravity

Fig 11.12


Projectiles with Horizontal Velocity

• One object fall as another object is projected horizontally.

• Which will hit the ground first?

Gravity acts on both objects equally

Horizontal velocity projects the object some distance from the release point


Projectiles with Vertical Velocity

• To affect time an object is in the air :– vertical velocity must be added. – height of release may be increased.

• Upward velocity will:– be slowed by gravity.– reach zero velocity. – gain speed towards the ground.– at height of release object will have the same

velocity it was given at release.


Projectiles with Vertical and Horizontal Velocities

• This is the case for most projectiles.• Horizontal velocity remains constant.• Vertical velocity subject to uniform acceleration

of gravity.

Fig 11.14


Horizontal Distance of a Projectile

• Depends on horizontal velocity & time of flight.• Time of flight depends on maximum height

reached by the object.– governed by vertical velocity of the object.

• Magnitude of these two vectors determined by:– initial velocity vector.– angle of projection.


Angle of Projection• Complementary angles of projection will have the

same landing point:– A & B– C & D– 450 angle (E)

• Throwing events may have a lower angle of projection, because of a difference in height of release and height of landing.

Fig 11.15


Factors that Control the Range of a Projectile

1.Velocity of Release

2.Angle of Projection

3.Height of Release

4.Height at Landing


Angular Kinematics

• Similar to linear kinematics.• Also concerned with displacement, velocity,

and acceleration.• Important difference is that they relate to

rotary rather than to linear motion.• Equations are similar.


Angular Displacement

• Skeleton is a system of levers that rotate about fixed points when force is applied.

• Particles near axis have displacement less than those farther away.

• Units of a circle:– Circumference = C– Radius = r– Constant (3.1416) = π

C = 2πr


Units of angular Displacement• Degrees:

– Used most frequently• Revolutions:

– 1 revolution = 360º = 2π radians• Radians:

– 1 radian = 57.3°

– Favored by engineers & physicists– Required for most equations

• Symbol for angular displacement - (theta)


Angular Velocity = / t

• Rate of rotary displacement - (omega).• Equal to the angle through which the radius

turns divided by time.• Expressed in degrees/sec, radians/sec, or

revolutions/sec.• Called average velocity because angular

displacement is not always uniform.• The longer the time span of the

measurement, the more variability is averaged.


Angular Velocity

• High-speed video:• 150 frames / sec

= .0067 sec / picture• Greater spacing, greater

velocity.• “Instant” velocity

between two pictures:a = 1432° / secb = 2864° /sec Fig 11.16


Angular Acceleration (alpha) is the rate of change of angular

velocity and expressed by above equation.

f is final velocity

i is initial velocity

= (f - i)/ t


Angular Acceleration

a is 25 rad/sec

b is 50 rad/sec

• Time lapse = 0.11 sec Fig 11.16

= f - i / t = (50 – 25) / 0.11 = 241 rad/sec/sec

Velocity increases by 241 radians per sec each second.


Relationship Between Linear and Angular Motion

• Lever PA > PB > PC• All move same angular distance in the same

time.

Fig 11.17



• Angular to linear displacement: s = r• C traveled farther than A or B, in the same time.• C had a greater linear velocity than A or B.• All three have the same angular velocity, but the linear

velocity of the circular motion is proportional to the length of the lever.

• If angular distance is constant, the longer the radius, the greater is the linear velocity of a point at the end of that radius.



• The reverse is also true.• If linear velocity is constant, an increase in

radius will result in a decrease in angular velocity, and vice versa.

Fig 11.18



• If one starts a dive in an open position and tucks tightly, angular velocity increases.– Radius of rotation decreases.– Linear velocity does not change.

• Shortening the radius will increase the angular velocity, and lengthening it will decrease the angular velocity.



• The relationship between angular velocity and linear velocity at the end of its radius is expressed by

• Equation shows the direct proportionality that exists between linear velocity and the radius.

= r


Chapter 11:The Description of

Human Motion

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© 2008 McGraw-Hill Higher Education. All Rights Reserved. Chapter 11: The Description of Human Motion KINESIOLOGY Scientific Basis of Human Motion, 11