Factors affecting the size of MI of a rotating body

• Factors that affect moment of inertia

  1. Mass
  2. Distribution of the mass from the axis of rotation
• Factor affecting MI - Mass

  • The greater the mass the greater the MI
  • The lower the mass , the easier it is to change the rate of rotation
• Sports with a high degree of rotation (eg high board diving ) are typically performed by athletes with a low body mass.
• Distribution of the mass from the axis of rotation

  • The further the mass moves from the axis of rotation , the greater the MI
  • The more closely mass is tucked in around the axis of rotation , the lower the MI , eg - tucked somersault
• When performing a tucked front somersault , the body will face less resistance to rotation and therefore will rotate more quickly compared with a straight front somersault
• MI has a direct effect on angular velocity

  • High MI = low angular velocity
  • Low MI = High angular velocity
• • If MI is high, resistance to rotation is also high , therefore angular velocity is low , the rate of spin is low.
• If MI is low , resistance to rotation is also low, therefore angular velocity is high , the rate of spin is fast.
• Conservation of angular momentum

  Angular momentum is a conserved quantity that remains constant unless an external eccentric force or torque is applied.
• Angular momentum

  • Once generated, does not change throughout a movement.
  • It remains constant
  • The conservation of angular momentum is a concept associated with the angular analogue of Newtons first law of motion.
• As angular momentum cannot be changed once in flight , it is important to generate as much angular momentum as possible before takeoff.
• Angular analogue of Newtons 1st Law of motion

  • The angular equivalent of Newtons first law of motion
  • A rotating body will continue to turn about an axis of rotation with constant angular momentum unless acted upon by an eccentric force or external torque.