9. Angular Motion

Question 1

Angular motion definition

Answer 1

Movement of a body or part of a body in a circular path about an axis of rotation

Question 2

Examples of angular motion

Answer 2

• A gymnast’s whole body will rotate around the high bar
• A trampolinist’s whole body rotates around their centre of mass during a somersault
• An athlete’s legs rotate at the hip joint as they run

Question 3

How is angular motion created?

Answer 3

Created by an eccentric force being applied to a body, where then force is applied outside the centre of a body’s mass.

Question 4

What is an eccentric force known as?

Answer 4

Torque - a turning or rotational force

Question 5

What is an axis of rotation?

Answer 5

An imaginary line that passes through the centre of mass about which a body rotates

Question 6

What are the 3 axis of rotation?

Answer 6

• Longitudinal -> spin on ice in ice skating
• Transverse -> somersault
• Frontal -> cartwheel

Question 7

What is angular velocity?

Answer 7

• The rate of change in angular displacement

Question 8

What is angular velocity measured in?

Answer 8

Radians per second (rad/s)

Question 9

What is a radian?

Answer 9

A unit of measurement of the angle through which a body rotates (360 degrees - 2 pye)

Question 10

Angular velocity equation

Answer 10

Angular displacement/time

Question 11

What is moment of inertia?

Answer 11

The resistance of a body to change its state of angular motion or rotation.
A resting body will not want to start rotating around an axis and will not change its angular motion or momentum.

Question 12

Moment of inertia equation

Answer 12

MI = sum (mass x distribution of mass from axis of rotation^2)

Question 13

What is moment of inertia measured in?

Answer 13

kgm^2

Question 14

What are the factors that affect MI?

Answer 14

• Mass -> the greater the mass of a body, the greater the moment of inertia and vice versa
• Distribution of mass from axis of rotation -> the further the mass moves from the axis of rotation, the greater the moment of inertia and vice versa.

Question 15

What is the relationship between MI and AV?

Answer 15

• If MI is high, resistance to rotation is high, therefore angular velocity is low, therefore the rate of spin is slow
• If MI is low, resistance to rotation is low, therefore angular velocity is high, therefore the rate of spin is fast

Question 16

What is angular momentum?

Answer 16

The quantity of angular motion possessed by a body
- It’s the rotational equivalent of momentum

Question 17

Angular momentum equation

Answer 17

Angular momentum = moment of inertia x angular velocity

Question 18

What is angular momentum measured in?

Answer 18

kgm^2/s

Question 19

What is conservation of angular momentum?

Answer 19

• Angular momentum is a conserved quantity which remains constant unless an external eccentric force or torque is applied. This means AM once generated does not change throughout a movement, it remains constant and is therefore termed a ‘conserved quantity’.
• This means once momentum has been generated, it is a product of MI and AV
• This means a performer can keep rotation for a long time, such as an ice skater performing a spin.