AQA · A-Level · Physical Education
Course version: 7582 · Version from Sept 2016
Conservation of angular momentum during flight, moment of inertia and its…
Full specification wording
Angular motion: Conservation of angular momentum during flight, moment of inertia and its relationship with angular velocity.
Angular momentum is the quantity of rotation a body possesses, calculated as moment of inertia × angular velocity.
Checked against the AQA 7582 specification (opens in a new tab) on .
- Point 4 of 4
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Angular momentum is the quantity of rotation a body possesses, calculated as moment of inertia × angular velocity. During flight, once a performer is airborne, no external torque acts about the axis of rotation, so angular momentum is conserved. Moment of inertia depends on how mass is distributed about the axis: a body with mass concentrated close to the axis has a small moment of inertia, while mass spread away increases it. Because angular momentum is constant in flight, moment of inertia and angular velocity are inversely related. A gymnast who tucks brings mass closer to the transverse axis, reducing moment of inertia and increasing angular velocity. Opening out increases moment of inertia and slows rotation, allowing a safe landing.
What earns the marks
- Angular momentum is the product of moment of inertia and angular velocity.
- During flight, angular momentum is conserved because no external torque acts about the axis of rotation.
- Moment of inertia depends on the distribution of mass about the axis of rotation.
- A tucked shape reduces moment of inertia by bringing mass closer to the transverse axis.
- Reduced moment of inertia produces a higher angular velocity when angular momentum is constant.
- Opening out increases moment of inertia and reduces angular velocity.
Common mistakes and how to put them right
Thinking angular momentum changes during flight.
Put it right: It is conserved when no external torque acts, so the product of moment of inertia and angular velocity stays constant.
Confusing moment of inertia with angular velocity.
Put it right: Moment of inertia is a measure of resistance to change in rotation, while angular velocity is the rate of rotation.
Believing a tucked shape increases angular velocity by adding force.
Put it right: The tuck reduces moment of inertia, and because angular momentum is conserved, angular velocity rises.
Exam tips
- Use the relationship angular momentum = moment of inertia × angular velocity to explain why a tuck speeds up rotation and opening out slows it.
- State clearly that angular momentum is conserved in flight because no external torque acts about the axis.
- Link each shape change to a change in moment of inertia first, then to the resulting change in angular velocity.
Try the lesson
The start of the Angular motion: Conservation of angular momentum during flight, moment of inertia and its relationship with angular velocity. lesson, made from checked teaching notes for this specification point.
Have a go first
A diver in mid-air tucks into a tight shape, reducing her moment of inertia. What happens to her angular velocity while she remains in flight?
Listen
Angular momentum is the quantity of rotation a body possesses, calculated as moment of inertia × angular velocity. During flight, once a performer is airborne, no external torque acts about the axis of rotation, so angular momentum is conserved. Moment of inertia depends on how mass is distributed about the axis: a body with mass concentrated close to the axis has a small moment of inertia, while mass spread away increases it. Because angular momentum is constant in flight, moment of inertia and angular velocity are inversely related. A gymnast who tucks brings mass closer to the transverse axis, reducing moment of inertia and increasing angular velocity. Opening out increases moment of inertia and slows rotation, allowing a safe landing. A strong answer earns marks for these points. Angular momentum is the product of moment of inertia and angular velocity. During flight, angular momentum is conserved because no external torque acts about the axis of rotation. Moment of inertia depends on the distribution of mass about the axis of rotation. A tucked shape reduces moment of inertia by bringing mass closer to the transverse axis. Exam tip: Use the relationship angular momentum = moment of inertia × angular velocity to explain why a tuck speeds up rotation and opening out slows it.
Key words
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Conservation of angular momentum
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Moment of inertia
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Application to flight in gymnastics and diving
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See every definition
- Conservation of angular momentum
- During flight, once a performer is airborne, no external torque acts about the axis of rotation, so angular momentum is conserved.
- Moment of inertia
- A body with mass concentrated close to the axis has a small moment of inertia, while mass spread away increases it.
- Application to flight in gymnastics and diving
- A gymnast who tucks brings mass closer to the transverse axis, reducing moment of inertia and increasing angular velocity, while opening out increases moment of inertia and slows rotation.
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