Chapter 11: The Description of Human Motion

1. Chapter 11:The Description of Human Motion KINESIOLOGY Scientific Basis of Human Motion, 10th edition Luttgens & Hamilton Presentation Created by TK Koesterer, Ph.D., ATC Humboldt State University

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 & 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

3. 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

4. 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 object’s inertia, or resistance to motion • Force relative to resistance will determine if the object will move or stay put

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 • Translatory or linear • Rotary or angular

6. 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

7. 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

8. 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

9. 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

10. 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

11. Kinds of Motion Experience by the Body • Most joints are axial • Undergo primarily angular motion • Slight translatory motion in gliding joints Fig 11.5

12. 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

13. 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

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

15. 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 sailboat’s motion, but may impede a runner • Water resistance is essential for propulsion, yet it hinders an objects progress through the water

16. 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?

17. 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

18. Linear Kinematics • Walk north 3 km, then east 4 km • What is the displacement? c2 = a2 + b2 c2 = 32 + 42 c = 25 c = 5 km Fig 11.8

19. 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

20. 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

21. 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

22. Acceleration Fig 11.10

23. Acceleration Units a = final velocity – initial velocity / times a = final m/sec – initial m/sec / sec a = m/sec / sec a = m/sec2

24. 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

25. 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

26. 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

27. 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

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 opposite • Upwards velocities are positive • Downward velocities are negative

29. 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

30. Projectiles • Follow a predictable path, a parabola • Gravity will • decelerate upward motions • accelerate downward motions • at 9.8 m/sec2 Fig 11.11

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. Factors that Control the Range of a Projectile • Speed of Release • Angle of Projection • Height of Release

38. 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

39. 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

40. 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)

41. 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

42. 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

43. Angular Acceleration  = v - u / t •  (alpha) is the rate of change of angular velocity and expressed by above equation • vis final velocity • u is initial velocity

44. 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

45. Relationship Between Linear and Angular Motion • Lever PA > PB > PC • Move same angular distance in the same time Fig 11.17

46. 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

47. 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

48. 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

49.  = r 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