How do rotation, torque and the conservation of angular momentum explain spinning and somersaulting movements?
Apply the principles of angular motion - torque, moment of inertia and conservation of angular momentum - to explain and improve rotating movements.
How torque, moment of inertia and conservation of angular momentum explain rotating movements such as somersaults, spins and throws, and how athletes control rotation speed.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
You must apply the principles of angular motion to explain rotating movements and to suggest how an athlete can control or improve rotation.
Torque: what starts rotation
Torque is the turning effect of a force applied at a distance from an axis. The larger the force and the further from the axis it acts (the longer the moment arm), the greater the torque. A gymnast generates torque to begin a somersault by pushing off the floor with force applied behind their centre of mass.
Moment of inertia: resistance to rotation
Moment of inertia is a body's resistance to a change in its rotation. It depends on the mass and, crucially, on how far that mass is distributed from the axis of rotation. Pulling mass close to the axis lowers the moment of inertia; spreading it out raises it.
- A tucked body (mass close to the axis) has a low moment of inertia and rotates fast.
- A straight or layout body (mass far from the axis) has a high moment of inertia and rotates slowly.
Angular momentum and its conservation
Angular momentum is the quantity of rotation a body has, equal to moment of inertia multiplied by angular velocity (spin speed). Once a performer leaves the ground, no external torque acts on them, so angular momentum is conserved: it stays constant for the whole flight.
Because the product is fixed in flight, changing one factor changes the other inversely. This is the key principle for controlling spins, somersaults and twists.
Applying it to performance
Athletes manipulate these principles deliberately:
- A figure skater pulls their arms in to spin faster and extends them to slow down.
- A long jumper uses arm and leg movements in flight to control rotation and land well, even though their angular momentum is fixed at take-off.
- A discus thrower lengthens the moment arm (a straight throwing arm) to apply more torque and impart more rotation and speed to the implement.