Physic Description of Human Motion

1. Physic Description of Human Motion Dr. Judith Ray

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

3. 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

4. Motion Displacement References Reference Points Tangent Speed Velocity Acceleration Translatory Rotary Rectilinear Curvilinear Reciprocating Oscillatory Linear Angular Terms to Remember about Motion

5. Causes of Motion Force Inertia General Motion Air Resistance Friction Projectiles Parabola Gravity Terms to Remember

6. External Factors Air Resistance Water Resistance Friction 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 Factors Modifying Motion

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

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

16. 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

17. 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

18. 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

19. 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

20. 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?

21. Displacement Velocity Acceleration Linear Pathway Linear Kinematics

22. 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

23. 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

24. 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

25. Linear Kinematics Fig 11.8

26. 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

27. 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

28. 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

29. Acceleration Fig 11.10

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

31. 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

32. 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

33. 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

34. 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

35. 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

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

37. 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

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

39. 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

40. 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

41. 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

42. 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

43. 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

44. 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

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

46. Angular KinematicsCircular and Rotational Motion • Displacement • Velocity • Acceleration

47. 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

48. 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

49. 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)

50. 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