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Biomechanics: Outline

Biomechanics: Outline. Definition Types of Motion Measuring Motion Describing the Geometry of Motion: Kinematics Linear Angular Describing the Forces of Motion: Kinetics Linear Angular Fluid Mechanics. Biomechanics.

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Biomechanics: Outline

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  1. Biomechanics: Outline • Definition • Types of Motion • Measuring Motion • Describing the Geometry of Motion: Kinematics • Linear • Angular • Describing the Forces of Motion: Kinetics • Linear • Angular • Fluid Mechanics

  2. Biomechanics • The study of the structure and functions of biological systems by means of the methods of mechanics Hatze, 1974 We might think of biomechanics as the “physics of human movement”

  3. Motion • Kinematics • describing movements with respect to time and space • Kinetics • examines the forces that produce the movement and result from the movement

  4. Why study biomechanics? • skill analysis • correction • pinpointing errors • developing a new technique • adapting to new equipment • understanding complex movement behavior

  5. Types of motion • Linear (translation) • all parts travel the same distance in the same time along the same path

  6. Type of Motion • Angular motion • parts rotate around an axis of rotation

  7. General Motion Most movements are likely a combination of both linear and angular motion

  8. Kinematics High speed cinematography High speed Videography Stroboscopy Optoelectric electrogoniometry accelerometry Kinetics Pressure and Force transducers Force Platform Isokinetic dynamometer Other Electromyography Measuring Motion

  9. Kinematics: Film Analysis SETUP CALIBRATION ANALYSIS

  10. What might we measure? KINEMATICS: Spatial component • Position • location in space relative to some spatial coordinate system reference (e.g., center of joint, COG, COM, point of contact) • Displacement • is the straight line distance and direction • Distance • the length of the path traversed

  11. What might we measure? • Center of gravity the point about which a body’s weight is equally balanced in all directions (Hall, 1995)

  12. Measuring Motion

  13. Kinematics: Film Analysis CALIBRATION SETUP ANALYSIS (50,490) ( (10, 570)

  14. Example: Data

  15. Example: Position and Velocity Data

  16. What might we measure? Kinematics: Spatial and temporal components • Speed • distance / time (m/s) • Velocity • displacement / time (m/s) • Acceleration • velocity / time (m/s2)

  17. What might we measure? Kinetics • Inertia • a body’s resistance to being moved • Force • a push or pulling action on the body (lbs, N) (nb: 1 lb = 4.45N)

  18. Motion, Force, and Sir Issac • First Law (Inertia) • a body continues in a state of rest or uniform motion until acted upon by an external force of sufficient magnitude to disturb its current state

  19. Motion, Force, and Sir Issac • Second Law (Acceleration or F=ma) • the acceleration of the body is proportional to the force exerted on it and inversely proportional to its mass e.g.1, a soccer ball (of fixed mass) will experience greater acceleration when kicked with more force e.g.2, for kick (of given force) a lighter soccer ball will experience greater acceleration

  20. Motion, Force, and Sir Issac • Third Law (action-reaction) • every action has an equal and opposite reaction (important for conservation of momentum)

  21. GROUND REACTION FORCES

  22. Angular Motion • When a force is not exerted along a line that passes through a body’s center of gravity (eccentric force), the body will experience angular (rotary) motion

  23. What might we measure? • Angular displacement • change in location of rotating body • Angular distance • angle between initial and final positions when measured by following the path of the body angular motion consider in degrees, revolutions, or radians 1 radian = 57.3 degrees 1 revolution = 360 degrees 1 revolution = 6.28 radians

  24. What might we measure? • Angular Velocity • angular displacement / time (degree/s) • Angular Acceleration • angular velocity / time (degrees/s2)

  25. What might we measure? Angular Kinetics • Torque • turning effect on a body measured as the product of force and moment arm length (e.g., changing tires) • Moment of inertia • resistance to rotary motion that results from combination of mass and distribution of the mass of an object • minimize resistance to angular rotation must move mass closer to axis of rotation (e.g., choking-up in baseball, spinning in skating or gymnastics)

  26. Moment of Interia: Relative • Tuck • Pike • Full body rotating around center of mass • Full body rotating around a bar

  27. Extended swing • around bar • Extended swing • around central axis • Pike • Tuck Assuming: Σmd2 Where: M = mass d = distance from axis of rotation

  28. Fluid Mechanics • Drag • Fluid force that opposes the forward motion of the body and reduced the body’s velocity. • Lift • Component of air resistance that is directed at right angles to the drag force

  29. Drag Fluid force that opposes the forward motion of the body and reduced the body’s velocity. Will depend on: • fluid density • frontal area of body (e.g., rowing shells) • drag coefficient (dependent on shape) • movement velocity

  30. Forms of Drag • Surface (hydrodynamic drag) • referring to interaction between body surface and the water • water temperature, water viscosity, body surface area, movement velocity • Profile (Form) • refers to resistive forces resulting from poor body position • Wave

  31. Surface Drag Water particles attract other water particles and will increase with “roughness of skin”

  32. Profile Drag • Low pressure pocket forms • and “holds back” the • cyclist. As velocity doubles this • resistive force quadruples!!!! • Important factors: • Shape • smoothness • orientation (crouch can lower • resistance ~30%

  33. Reducing Drag • Frame designs • on bikes are often • “tear-shaped” to • reduce drag • Drafting within 1 m • can reduce drag • accounting for 6% of • energy cost (e.g., ducks flying)

  34. Lift Component of air resistance that is directed at right angles to the drag force Lift Resultant Drag Air Flow

  35. High velocity/Low Pressure Low velocity/High Pressure Lift - common example According to Bernoulli's Law, faster air has lower air pressure, and thus the high pressure beneath the wing pushes up to cause lift.

  36. Lift and Formula I • The desire to further increase the tire adhesion led the major revolution in racing car design, the introduction of inverted wings,which produce negative lift or 'downforce'.

  37. http://www.npl.uiuc.edu/%7Ea-nathan/pob/index.html

  38. Magnus Effect Intended Direction Flight Path • Force first discovered by Magnus. It explains the curving of a spinning ball. As the spinning object pushes the air from one side to the other, it will create a lower pressure zone, making the object move faster on one side. Air Flow Low Pressure

  39. Kinematics linear motion displacement, velocity.. Angular Motion angular displacement… Kinetics linear motion mass, inertia Angular Motion torque, moment of inertia Review • Fluid dynamics • drag • lift

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