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The final principle is unique in nature as it only applies to objects which are airborne or on surfaces which have extremely low coefficients of friction. An excellent example of this principle is figure skaters. Have you ever watched a figure skating competition and wondered how the athletes are able to complete a stationary spin on ice while increasing and decreasing their rate of spin. This motion is made possible due principle #7 and the conservation of angular momentum.

Angular momentum is the product of inertia (a body’s resistance to changes in motion) and that body’s angular velocity. As a result, in order to maintain a constant angular momentum, the figure skater can manipulate their body in order to increase its inertia, while subsequently decreasing its angular velocity or visca versa. In the figure skating example, the figure skaters will utilize their arms in order to decrease their inertia (bring the arms closer to their body) which in turn causes them to increase their rate of spin or angular velocity. As they near the end of the spin, they will move their arms further away from their body (increasing their inertia) which in turn will cause a decrease in their angular velocity and slow down their rate of spin.

This principle also plays a vital role in the success of elite level divers. When the diver moves from a layout position to a tuck position, they are ultimately manipulating their moment of inertia in order to adjust their angular velocity. If the divers timing is off, they will not make a clean entrance into the pool. This is part of the reason why you will see divers break form (ie. flex the knees) near the completion of their jump in order to increase their velocity in hopes of making a cleaner entrance into the pool. Elite level divers are extremely gifted in knowing where they should be when coming out of a dive in order to make a clean entrance into the water. This is where repetition and quality feedback from the coach and/or Biomechanist can help to improve the diver’s performance and overall score on a dive.

Brian Shackel, MSc