Angular motion part 2

Question 1

3 descriptors important to angular motion are

Answer 1

1. Angular velocity
2. Moment of inertia
3. Angular momentum

Question 2

Angular velocity

Answer 2

Definition = the rate of change in an angular displacement (speed of rotation)

Measured in = radians per seconds (rad/s)

Formula = Angular displacement / time

Question 2

Example of angular velocity

Answer 2

A trampolinist performing a front flip rotated their body about the axis 6.28 radians in 0.5 seconds.
Angular velocity = 6.28 / 0.5 = 12.56 rad/s

Question 3

2. Moment of inertia

Answer 3

Definition = the resistance of a body/object to angular motion (rotation).

Dependent on:
Mass of body
Distribution of the mass from the axis

Question 4

Formula for moment of inertia

Answer 4

Moment of inertia =
mass x distribution of the mass from the axis of rotation (squared)
Units = kgm2

Question 5

3. Angular momentum

Answer 5

Definition = the quantity of rotation a body possesses.

It depends on:
- the moment of inertia
- angular velocity

Formula = moment of inertia x angular velocity.

Question 6

Conservation of angular momentum

Answer 6

• it is a conserved quantity which means it stays constant, unless an external force acts upon it.

Question 7

Angular displacement

Answer 7

as an object moves from A to B they move through a certain angle.
- measured in radians
- radian is an angle of 57.3 degrees

Question 8

Question
1. Define the term angular velocity. Give an equation for its calculation and state the units it’s measured in. (3)

Answer 8

Rate of change in angular displacement
Angular displacement / time
rad/s

Question 9

Question
2. An ice skater spins about their longitudinal axis by generating angular momentum.
Use the angular analogue of newtons 1st law of motion to explain how the skater can increase their rate of spin. (4)

Answer 9

The skater will bring their arms and legs closer in to the longitudinal axis of rotation.
This will reduce the moment of inertia, increasing angular velocity. Which proves that Angular momentum = moment of inertia x angular velocity.