CHAPTER 11:PART 1 THE DESCRIPTION OF HUMAN MOTION

Transcription

1 CHAPTER 11:PART 1 THE DESCRIPTION OF HUMAN MOTION KINESIOLOGY Scientific Basis of Human Motion, 12 th 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.

2 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. 11A-2

3 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. 11A-3

4 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. 11A-4

5 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 11A-5

6 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 A-6

7 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. 11A-7

8 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 A-8

9 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. 11A-9

10 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 A-10

11 Kinds of Motion Experienced by the Body Most joints are axial. Segments undergo primarily angular motion. Slight translatory motion in gliding joints. Fig A-11

12 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 A-12

13 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 11A-13

14 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. 11A-14

15 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. 11A-15

16 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. 11A-16

17 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. 11A-17

18 Linear Kinematics Walk north 3 km, then east 4 km. What is the distance traveled? What is the displacement? Fig A-18

19 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 11A-19

20 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 v s t 11A-20

21 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 v f v i t or v t 11A-21

22 Acceleration Fig 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 (-) 11A-22

23 Acceleration Units a = (final velocity initial velocity)/time a = (final m/sec initial m/sec)/sec a = (m/sec)/sec a = m/sec 2 11A-23

24 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. 11A-24

25 Acceleration Due to 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. 11A-25

26 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. 11A-26

27 Laws of Uniformly Accelerated Motion Distance traveled & velocity can be determined for any point in time when acceleration is constant: v f v i at s v i t at 2 v f 2 v i 2 2as Where: v f = final velocity v i = initial velocity a = acceleration t = time s = displacement 11A-27

28 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. 11A-28

29 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. 11A-29

30 Projectiles Follow a predictable path, a parabola. Gravity will slow upward motion, increase downward motion. at 9.8 m/sec 2. Fig A-30

31 Projectiles Upward portion Position versus Time Upward Velocity versus Time Upward Position y-direction (m) Velocity y-direction (m/s) Time (sec) Time (sec) Acceleration versus Time Upward Acceleration y-direction (m/s 2 ) Time (sec) 11A-31

32 Projectiles Downward portion Position versus Time Downward Velocity versus Time Downward Position y-direction (m) Velocity y-direction (m/s) Time (sec) Time (sec) Acceleration versus Time Downward Acceleration y-direction (m/s 2 ) Time (sec) 11A-32

33 Projectiles Initial velocity at an angle of projection: Components Vertical velocity: affected by gravity Horizontal velocity: not affected by gravity Fig A-33

34 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 11A-34

35 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. 11A-35

36 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 A-36

37 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. 11A-37

38 Angle of Projection Complementary angles of projection will have the same landing point: A & B C & D 45 0 angle (E) Throwing events may have a lower angle of projection, because of a difference in height of release and height of landing. Fig A-38

39 Factors that Determine the Range of a Projectile 1. Velocity at release 2. Angle of projection 3. Height of release 4. Height at landing 11A-39