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CHAPTER 11:PART 1
THE DESCRIPTION OF
HUMAN MOTION
KINESIOLOGY
Scientific Basis of Human Motion, 12th edition
Hamilton, Weimar & Luttgens
Presentation Created by
TK Koesterer, Ph.D., ATC
Humboldt State University
Revised by Hamilton & Weimar
McGraw-Hill/Irwin
Copyright © 2012 by The McGraw-Hill Companies, Inc. All rights reserved.
Objectives
1. 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 .
Motion: 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.
Cause 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.
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:
 Linear or translatory
 Angular or rotary
Translatory Movement
 An object is translated as a whole from one
location to another.
 Rectilinear: straight-line progression
 Curvilinear: curved translatory movement
Curvilinear
motion
Rectilinear
motion
Fig 11.1
Fig 11.2
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.
Angular, 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
Angular, 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 fashion
 ball is moving with circular motion.
 arm acts as a radius moving with angular motion.
0
Other Movement Patterns
 Combinations 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
1
Kinds of Motion
Experienced by the Body
 Most joints are axial.
 Segments undergo
primarily angular
motion.
 Slight translatory
motion in gliding
joints.
Fig 11.5
2
Kinds 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 11.7
Fig 11.6
3
Kinds of Motion
Experienced 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
4
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 linear or angular motion.
 Determined by where force is applied in reference
to its center of gravity.
 Presence or absence of modifying forces.
5
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.
6
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.
 Major problems in movement are:
 How to take advantage of these factors.
 How to minimize them when they are
detrimental to the movement.
7
Kinematic Description of Motion
Linear Kinematics
 Distance
 How far an object has 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.
8
Linear Kinematics
 Walk north 3 km, then east 4 km.
 What is the distance traveled?
 What is the displacement?
Fig 11.8
9
Speed 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
0
Speed and Velocity
 Velocity involves direction as well as speed.
 Speed in a given direction
 Rate of displacement
 A vector quantity
Average Velocity = displacement or s
time
t
s
v
t
1
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 velocity
time
v f  v i v
a
or
t
t
2
Acceleration
Fig 11.10
Section a:
Section b:
Section c:
Section d:
v- increasing (+)
v- constant (+)
v- non-linear increase (+)
v- decreasing (+)
a-constant (+)
a-zero
a- non-constant (+)
a- constant (-)
3
Acceleration Units
a = (final velocity – initial velocity)/time
a = (final m/sec – initial m/sec)/sec
a = (m/sec)/sec
a = m/sec2
4
Uniformly 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.
5
Acceleration 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/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.
6
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.
7
Laws of Uniformly
Accelerated Motion
 Distance traveled & velocity can be
determined for any point in time when
acceleration is constant:
Where:
v f  v i  at
vf = final velocity
at 2
v
=
initial
velocity
i
s  vit 
a = acceleration
2
t = time
v f  v i 2  2as
s = displacement
8
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
in opposite directions.
 Upward velocities are positive.
 Downward velocities are negative.
9
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.
0
Projectiles
 Follow a predictable
path, a parabola.
 Gravity will
 slow upward motion,
 increase downward motion.
 at 9.8 m/sec2.
Fig 11.11
1
Projectiles
Upward portion
Velocity y-direction (m/s)
Velocity versus Tim e
Upw ard
6
5
4
3
2
1
0
0
0.2
0.4
0.6
0.8
1
10
8
6
4
2
0
0
1.2
0.2
0.4
0.6
Time (sec)
Time (sec)
Acceleration versus Tim e
Upw ard
Acceleration y-direction
(m/s2)
Position y-direction (m)
Position versus Tim e
Upw ard
0
-2 0
0.2
0.4
0.6
-4
-6
-8
-10
-12
Time (sec)
0.8
1
1.2
0.8
1
1.2
2
Projectiles
Downward portion
Velocity versus Tim e
Dow nw ard
Velocity y-direction (m/s)
6
5
4
3
2
1
0
0
0.2
0.4
0.6
0.8
1
1.2
0
-2
0
0.2
0.4
0.6
-4
-6
-8
-10
Time (sec)
Time (sec)
Acceleration versus Tim e
Dow nw ard
Acceleration y-direction
(m/s2)
Position y-direction (m)
Position versus Tim e
Dow nw ard
0
-2 0
0.2
0.4
0.6
-4
-6
-8
-10
-12
Time (sec)
0.8
1
1.2
0.8
1
1.2
3
Projectiles
 Initial velocity at an angle of projection:
 Components
 Vertical velocity: affected by gravity
 Horizontal velocity: not affected by gravity
Fig 11.12
4
Projectiles 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
5
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.
6
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
7
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.
8
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
9
Factors that Determine the Range
of a Projectile
1.
2.
3.
4.
Velocity at release
Angle of projection
Height of release
Height at landing