angular motion

• Angular motion:

  • ALWAYS has an axis of rotation (line perpendicular to plane of rotation).

  Axis of rotations= anteroposterior, longitudinal, and mediolateral.
• Angles-three units of measurement:

  ·      Degree (useful for joint angles/quantitative analysis).

  ·      Revolution (used for qualitative description).

  ·      Radian (ø=2 RAD per 360˚. ).
• Radian= unitless/not considered in calculation

  (must use radians when involving linear motion).
• Absolute angle: segments.

  ·      Segment angle relative to fixed reference in environment.

  Relative angle: joints.

  ·      Angle between longitudinal axes of two segments.
• Angular motion vector: need to establish direction of rotation.

  +/- determined by cartesian plane for linear motion.

  Polarity of vector- right hand thumb rule for angular motion
• ·      Angular distance= total angular change following its exact path.

  ·       Angular displacement= difference between initial and final positions of rotating objects (displacementx = finalx – intialx).
• (angular distance=radius (m) x angle (radians))
• • Angular speed= angular distance travelled per unit of time (scalar).
  • Angular velocity (w)= vector quantity that describes rate of change in angular position (angular displacement (ø)/time (t))
• When other factors are constant:

  greater radius of rotation of a swinging object= greater linear velocity at the end of the swinging object.
• ·ANGULAR ACCELERATION

  • Also a vector (has a direction)
  • Measure of the rate of change of angular velocity.
  • Angular velocity (a alpha) = ∆ angular velocity/ ∆ time
• Tangential acceleration:

  ·      Tangent (perpendicular to radius) of angular motion path.

  ·      Change in linear speed.

  
• Centripetal (radial) acceleration:

  • Parallel to radius.
  • Measure of change in direction.
  • angular velocity.

  Large tangential velocity or smaller radius= increase in centripetal acceleration