CHAPTER 11:PART 1THE DESCRIPTION OF

HUMAN MOTION

CHAPTER 11:PART 1THE DESCRIPTION OF

HUMAN MOTION

KINESIOLOGYScientific Basis of Human Motion, 12th edition

Hamilton, Weimar & LuttgensPresentation Created by

TK Koesterer, Ph.D., ATCHumboldt State University

Revised by Hamilton & Weimar

Copyright © 2012 by The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill/Irwin

11A-2

ObjectivesObjectives1. Name the motions experienced by the human body,

and describe the factors that cause & modify motion.

2. Name & properly use terms that describe linear & angular 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 & angular movement, & explain significance to human motion.

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

11A-3

Motion: Relative MotionMotion: 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

airplane:At rest in reference to the airplane.In motion in reference to the earth.

11A-4

Cause of MotionCause of Motion

The cause of motion is some 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.

11A-5

Kinds of MotionKinds 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:Linear or translatory Angular or rotary

11A-6

Translatory MovementTranslatory Movement

An object is translated as a whole from one location to another.Rectilinear: straight-line progressionCurvilinear: curved translatory

movement

Fig 11.1 Fig 11.2

Rectilinear Rectilinear motionmotion

CurvilinearCurvilinearmotionmotion

11A-7

Circular MotionCircular MotionA 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.

11A-8

Angular, or Rotary, MotionAngular, or Rotary, 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

11A-9

Angular, or Rotary, MotionAngular, or Rotary, 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 fashionball is moving with circular motion.arm acts as a radius moving with angular

motion.

11A-10

Other Movement PatternsOther Movement PatternsCombinations of linear & angular motion

are called general motion

Angular motions of forearm, upper arm & legs.

Hand travels linearly and imparts linear force to the foil.

Fig 11.4

11A-11

Kinds of Motion Experienced by the BodyKinds of Motion Experienced by the Body

Most joints are axial.

Segments undergo primarily angular motion.

Slight translatory motion in gliding joints.

Fig 11.5

11A-12

Kinds of Motion Experienced by the BodyKinds of Motion Experienced by the Body

Linear movement when the body is acted on by the force of gravity or a linear external force.

Fig 11.7Fig 11.6

11A-13

Kinds of Motion Experienced by the BodyKinds of Motion Experienced by the BodyGeneral 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

11A-14

Factors that Determine the Kind of MotionFactors that Determine the Kind of MotionDepends 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 linear or angular motion.Determined by where force is applied in

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

11A-15

Factors Modifying MotionFactors Modifying MotionExternal 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.

11A-16

Factors Modifying MotionFactors Modifying MotionInternal 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.

Major problems in movement are:How to take advantage of these factors.How to minimize them when they are

detrimental to the movement.

11A-17

Kinematic Description of MotionKinematic Description of Motion

DistanceHow far an object has traveled.

DisplacementDistance an object has moved from a

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

and direction.

Linear KinematicsLinear KinematicsLinear KinematicsLinear Kinematics

11A-18

Linear Kinematics Linear Kinematics Walk north 3 km, then east 4 km.

What is the distance traveled?

What is the displacement?

Fig 11.8

11A-19

Speed and VelocitySpeed and Velocity

Speed is how fast an object is moving, without regard to the direction of movement.a scalar quantity

Average Speed = distance traveled or d

time t

11A-20

Velocity involves direction as well as speed.Speed in a given directionRate of displacementA vector quantity

Average Velocity = displacement or s time t

Speed and VelocitySpeed and Velocity

v s

t

11A-21

AccelerationAccelerationThe 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 v f v it

orvt

11A-22

AccelerationAcceleration

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 (-)

11A-23

Acceleration UnitsAcceleration Units

a = (final velocity – initial velocity)/time

a = (final m/sec – initial m/sec)/sec

a = (m/sec)/sec

a = m/sec2

11A-24

Uniformly Accelerated MotionUniformly Accelerated Motion

Constant acceleration.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.

11A-25

Acceleration Due to GravityAcceleration Due to 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/secEnd of 2 sec = 19.6 m/secEnd of 3 sec = 29.4 m/sec

Does not consider resistance or friction of air.

11A-26

Air Resistance Air ResistanceLighter 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.

11A-27

Laws of Uniformly Accelerated MotionLaws of Uniformly Accelerated Motion

Distance traveled & velocity can be determined for any point in time when acceleration is constant:

Where:vf = final velocity

vi = initial velocity

a = accelerationt = times = displacement

v f v i at

sv it at 2

2

v f v i2 2as

11A-28

Laws of Uniformly Accelerated MotionLaws of Uniformly Accelerated MotionTime 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 in opposite directions.Upward velocities are positive.Downward velocities are negative.

11A-29

ProjectilesProjectilesObjects given an initial velocity and

released.

Gravity is the only influence after release.*

Maximum horizontal displacemente.g. long jumper, shot-putter

Maximum vertical displacemente.g. high jumper, pole vault

Maximum accuracye.g. shooting in basketball or soccer

* Neglecting air resistance.

11A-30

ProjectilesProjectiles

Follow a predictable path, a parabola.

Gravity will slow upward motion, increase downward motion.at 9.8 m/sec2.

Fig 11.11

11A-31

ProjectilesProjectilesUpward 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)

11A-32

ProjectilesProjectilesDownward 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)

11A-33

ProjectilesProjectilesInitial velocity at an angle of projection:

ComponentsVertical velocity: affected by gravityHorizontal velocity: not affected by gravity

Fig 11.12

11A-34

Projectiles with Horizontal VelocityProjectiles with Horizontal Velocity

One object falls as another object is projected horizontally.• Which will hit the ground first?

Gravity acts on both objects equally

Horizontal velocity carries the object some distance from the release point

11A-35

Projectiles with Vertical VelocityProjectiles 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.

11A-36

Projectiles with Vertical and Horizontal VelocitiesProjectiles 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

11A-37

Horizontal Distance of a ProjectileHorizontal Distance of a ProjectileDepends 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.

11A-38

Angle of ProjectionAngle of ProjectionComplementary angles of projection will

have the same landing point:A & BC & D450 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

11A-39

Factors that Determine the Range of a ProjectileFactors that Determine the Range of a Projectile

1. Velocity at release2. Angle of projection3. Height of release4. Height at landing