Physic Description of Human Motion

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Physic Description of Human Motion

• Dr. Judith Ray

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

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Objectives

• 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

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Terms to Remember about Motion

• Motion
• Displacement
• References
• Reference Points
• Tangent
• Speed
• Velocity
• Acceleration

• Translatory
• Rotary
• Rectilinear
• Curvilinear
• Reciprocating
• Oscillatory
• Linear
• Angular

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Terms to Remember

• Causes of Motion
• Force
• Inertia
• General Motion
• Air
• Resistance
• Friction

• Projectiles
• Parabola
• Gravity

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Factors Modifying Motion

• Internal Factors and Anatomical factors
• 1. friction is joints
• 2. tension of antagonists, ligaments fasciae
• 3. anomalies of bone joint structure
• 4. atmospheric pressure inside joints
• 5. and presence of interfering soft tissues

• External Factors
• Air Resistance
• Water Resistance
• Friction

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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

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Cause of Motion

• Each cause of motion is a form of force
• Force is the instigator of movement
• Force must be sufficiently great to overcome the
  objects inertia, or resistance to motion
• Force relative to resistance will determine if
  the object will move or stay put

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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

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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
Fig 11.2
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Circular Motion

• A special form of curvilinear motion
• Does not appear to be translatory
• 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

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Rotary, or Angular, Motion

• Typical of levers, wheels, axels
• Object acting as a radius moves about a fixed
  point
• Measured as an angle, in degrees
• Body parts move in an arch about a fixed point

Fig 11.3
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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 arm moves in a windmill
  fashion,
• ball is moving with circular motion
• arm acts as a radius moving with angular motion

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Other Movement Patterns

• Combination of rotary translatory is called
  general motion
• Angular motions of forearm upper arm
• Hand travels linearly and impart linear force to
  the foil

Fig 11.4
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Kinds of Motion Experience by the Body

• Most joints are axial
• Undergo primarily angular motion
• Slight Translatory motion in gliding joints

Fig 11.5
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Kinds of Motion Experience by the Body

• Rectilinear movement when the body is acted on by
  the force of gravity or an external force

Fig 11.7
Fig 11.6
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Kinds of Motion Experience by the Body

• General motion
• forward and backward rolls on ground
• Rotary motion
• twirling on ice skates
• Curvilinear translatory motion
• in diving and jumping
• Reciprocating motion
• swinging on a swing

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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
• Where force is applied reference to its center of
  gravity
• Presence or absence of modifying forces

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Factors Modifying Motion

• External factors
• Friction helps a runner gain traction, but hinder
  the rolling of a ball
• Air resistance or wind is indispensable to the
  sailboats motion, but may impede a runner
• Water resistance is essential for propulsion, yet
  it hinders an objects progress through the water

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Factors Modifying Motion

• Internal or anatomical factors friction is
  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 then when they are detrimental to
  the movement?

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Linear Kinematics

• Displacement
• Velocity
• Acceleration

• Linear Pathway

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KINEMATIC DESCRIPTION OF MOTIONLinear Kinematics

• Distance Displacement
• distance an object moved form a reference point
  is called displacement
• does not indicate how far object traveled
• A vector quantity having both magnitude and
  direction

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KINEMATIC DESCRIPTION OF MOTIONLinear Kinematics

• Distance Displacement
• distance an object moved form a reference point
  is called displacement
• does not indicate how far object traveled
• A vector quantity having both magnitude and
  direction

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Linear Kinematics

• Walk north 3 km, then east 4 km
• What is the displacement?
• c2 a2 b2
• c2 32 42
• c Square root of 25
• c 5 km

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Linear Kinematics
Fig 11.8
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Speed and Velocity

• Speed is how fast an object is moving, nothing
  about the direction of movement
• a scalar quantity
• Average Speed direction traveled or d
• time
  t

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Speed and Velocity

• Velocity involves direction as well as speed
• speed in a given direction
• a rate of displacement
• a vector quantity
• Average Velocity displacement or s / t
• time
  
• ? s / t

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Acceleration

• The rate of change of velocity
• May be positive or negative
• Increase is positive, decrease is slowing
• Negative acceleration is deceleration

Average acceleration final velocity initial
velocity time a ? - u / t
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Acceleration
Fig 11.10
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Acceleration Units

• a final velocity initial velocity / times
• a final m/sec initial m/sec / sec
• a m/sec / sec
• a m/sec2

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Uniformly Accelerated Motion

• Constant acceleration rate
• Does not occur often
• 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

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Acceleration of Gravity

• 32 ft/sec2 or 9.8 m/sec2
• Velocity will increase 9.8 m/sec
• End of 1 sec 9.8 m/sec
• End of 2 sec 19.6 m/sec
• End of 3 sec 29.4 m/sec
• Do not consider resistance or friction of air

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Air Resistance or Friction of Air

• Lighter objects will be affected more
• may stop accelerating (feather) and fall at a
  constant rate
• Denser, heavier objects are affected less
• Terminal velocity friction of air is increased
  to equal accelerating force of gravity
• Object no longer is accelerating
• Sky diver approximately 120 mph or 53 m/sec

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Laws of Uniformly Accelerated Motion

• Distance traveled downward velocity can be
  determined for any point in time
• ? u at
• s ut 1/2at2
• ?2 u2 2as

Where ? velocity u initial velocity a
acceleration t time s displacement
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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

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Projectiles

• Objects or bodies moving effected by external
  forces of liquids (air or water)
• Gravity
• Buoyancy

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Projectiles

• Objects given an initial velocity and released
• Gravity influences
• Maximum horizontal displacement
• long jumper, shot-putter
• Maximum vertical displacement
• high jumper, pole vault
• Maximum accuracy
• shooting in basketball or soccer

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Projectiles

• Follow a predictable path, a parabola
• Gravity will
• decelerate upward motions
• accelerate downward motions
• at 9.8 m/sec2

Fig 11.11
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Projectiles

• Vector projective force gravity
• Initial velocity at an angle of projection
• Components
• Vertical affected by gravity
• Horizontal not affected by gravity

Fig 11.12
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Projectiles with Horizontal Velocity

• One object fall as other 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
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Projectiles with Vertical Velocity

• To affect time of object is in the air
• vertical velocity must be add
• alter the height of release
• Project with only upward velocity will
• decelerate by gravity
• reach zero velocity
• accelerate towards the ground
• at release point has the same velocity it was
  given at release

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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
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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 projection velocity vector
• angle of direction of this vectors

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Angle of Projection

• Low angle
• Large angle
• 450 angle
• Throwing events may have a lower optimum
  projection, because of height of release

Fig 11.15
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Factors that Control the Range of a Projectile

1. Speed of Release
2. Angle of Projection
3. Height of Release

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Angular KinematicsCircular and Rotational Motion

• Displacement
• Velocity
• Acceleration

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Angular Kinematics

• Similar to linear kinematics
• Also concerned with displacement, velocity, and
  acceleration
• Important difference is that they related to
  rotary rather than to linear motion
• Equations seems similar
• units used to describe them are different

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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) ?

C 2?r
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Units of angular Displacement

• Degrees
• Used most frequently
• Revolutions
• 1 revolution 3600 2? radians
• Radians
• 1 radian 57.30
• Favored by engineers physicists
• Required for most equations
• Symbol for angular displacement - ? (theta)

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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 of a skill is not uniform
• Longer time span of measure, the more variability
  is averaged

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Angular Velocity

• High-speed video
• 150 frames / sec .0067 sec / picture
• Greater spacing greater velocity
• Instant velocity between two pictures
• a 14320 / sec
• b 28640 sec

Fig 11.16
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Angular Acceleration
? ?v - ?u / t

• ? (alpha) is the rate of change of angular
  velocity and expressed by above equation
• ?v is final velocity
• ?u is initial velocity

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Angular Acceleration

• a is 25 rad/sec
• b is 50 rad/sec
• Time lapse 0.11 sec

Fig 11.16
? ?v - ?u / t ? 50 25 / 0.11 ? 241
rad/sec/sec
241 radians per sec each second
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Combining Linear and Angular Kinematics

• Straight things moving in circular motion
• Round things moving in linear motion

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Relationship Between Linear and Angular Motion

• Lever PA gt PB gt PC
• Move same angular distance in the same time

Fig 11.17
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Relationship Between Linear and Angular Motion

• C traveled farther than A or B
• Angular to linear displacement s ?r
• C moved a grater linear velocity than A or B
• All three have the same angular velocity, but
  linear velocity of the circular motion is
  proportional to the length of the lever
• If angular is constant, the longer the radius,
  the greater is the linear velocity of a point at
  the end of that radius

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Relationship Between Linear and Angular Motion

• Reverse is also true
• If linear velocity is constant, an increase in
  radius will result in a decrease in angular
  velocity

Fig 11.18
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Relationship Between Linear and Angular Motion

• If one starts a dive in an open position and
  tucks tightly, angular velocity increases
• Radius of rotation decreases
• Linear velocity does not changes
• Shortening the radius will increase the angular
  velocity, and lengthening it will decrease the
  angular velocity

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Relationship Between Linear and Angular Motion

• The relationship between angular velocity and
  linear velocity at the end of its radius is
  expressed by
• Equation shows the direct proportionality that
  exist between linear velocity and the radius

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Summary and Discussion

• Linear and Angular Kinematics
• Projectiles and all of its properties
• Putting it all together
• Identify kinematic components used to describe
  skillful performance of a motor task