Chapter 11 The Description of Human Motion KINESIOLOGY
- Slides: 52
Chapter 11: The Description of Human Motion KINESIOLOGY Scientific Basis of Human Motion, 11 th edition Hamilton, Weimar & Luttgens Presentation Created by TK Koesterer, Ph. D. , ATC Humboldt State University Revised by Hamilton & Weimar © 2008 Mc. Graw-Hill Higher Education. 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 & 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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Translatory Movement • An object is translated as a whole from one location to another. – Rectilinear: straight-line progression – Curvilinear: curved translatory movement Curvilinear motion Fig 11. 1 Rectilinear motion Fig 11. 2 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Linear Kinematics • Walk north 3 km, then east 4 km. • What is the distance traveled? • What is the displacement? Fig 11. 8 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 / t time v=s/t © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 a = (vf – vi)/t © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 (-) © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Acceleration Units a = (final velocity – initial velocity) / time a = (final m/sec – initial m/sec) / sec a = (m/sec) / sec a = m/sec 2 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Acceleration of Gravity • 32 ft/sec 2 or 9. 8 m/sec 2 • 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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Laws of Uniformly Accelerated Motion • Distance traveled & downward velocity can be determined for any point in time: vf = vi + at s = vi t + /2 at 2 vf 2 = vi 2 + 2 as Where: vf = final velocity vi = initial velocity a = acceleration t = time s = displacement © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Projectiles • Follows a predictable path, a parabola. • Gravity will – slow upward motion. – increase downward motion. – at 9. 8 m/sec 2 Fig 11. 11 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Projectiles Upward portion © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Projectiles Downward portion © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Projectiles • Initial velocity at an angle of projection: – Components • Vertical velocity: affected by gravity • Horizontal velocity: not affected by gravity Fig 11. 12 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Factors that Control the Range of a Projectile 1. Velocity of Release 2. Angle of Projection 3. Height of Release 4. Height at Landing © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 C = 2πr – Radius = r – Constant (3. 1416) = π © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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) © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Angular Velocity • High-speed video: • 150 frames / sec =. 0067 sec / picture • Greater spacing, greater velocity. • “Instant” velocity between two pictures: a = 1432° / sec b = 2864° /sec Fig 11. 16 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Angular Acceleration = ( f - i)/ t • (alpha) is the rate of change of angular velocity and expressed by above equation. – f is final velocity – i is initial velocity © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 Velocity increases by 241 radians per sec each second. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Relationship Between Linear and Angular Motion • Lever PA > PB > PC • All move same angular distance in the same time. Fig 11. 17 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Relationship Between Linear and Angular Motion • • 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. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Relationship Between Linear and Angular Motion • 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 © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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 change. • Shortening the radius will increase the angular velocity, and lengthening it will decrease the angular velocity. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Relationship Between Linear and Angular Motion • The relationship between angular velocity and linear velocity at the end of its radius is = r expressed by • Equation shows the direct proportionality that exists between linear velocity and the radius. © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
Chapter 11: The Description of Human Motion © 2008 Mc. Graw-Hill Higher Education. All Rights Reserved.
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