Physical phenomena related to moment of inertia in real life

In the Olympic figure skating competition, when an athlete wants to spin quickly in the air, he always opens his arms first, and then contracts his arms at the moment of take-off and rotation, so that he can spin quickly. This is to use angular momentum to maintain balance. Angular momentum = moment of inertia * angular velocity. When the moment of inertia of the telescopic arm decreases, the angular velocity increases. Therefore, when athletes spin in the air, their arms are contracted. Another application is the general instrument on the plane.