One must understand Newton’s laws of motion and the concept of friction in order to understand how a person skates. You know that friction is a force that resists when two objects slide against each other. Ice floor has much less friction compared to the ground. It does not offer much resistance to the object that comes into contact. At the same time, some friction is needed in order to let the skater start the motion. The first law of motion says an object in motion tends to stay in motion unless acted on by a force. This is the reason why skaters are in motion continuously unless they use force to stop themselves.
Also Newton’s third law states that for every action there is an equal and opposite reaction. When the skaters move across the ice, they are applying a force down and back against the ground. There is an equal and opposite force given by the ground which provides a forward push allowing the skater to glide easily.
Any object that is in motion has ‘momentum’. When we talk about momentum, we refer to a ‘mass in motion’. Heavier is the object, faster it is moving and more momentum is needed to slow it down. Angular momentum applies to a body rotating around a fixed object. The amount of angular momentum depends on the speed of rotation, weight and distribution of the mass around the center. For two skaters of the same mass rotating at the same speed, the one with its mass more extended in space will have the greater angular momentum.
There is a fundamental law of physics that says momentum is always conserved. That means unless some outside force enters a system, its total momentum must stay constant. When the skater’s arms are outstretched, the mass of the body is distributed over a greater space. When the skater draws his/her arm inwards, the distribution of mass is reduced, and so the speed must pick up to counteract the difference and keep the total momentum constant. This is why a skater spins more quickly when the skater pulls in his/her arms and executes a turn.
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