Angular Motion

Question 1

What is angular motion?

Answer 1

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

Question 2

What type of force is required to create angular motion?

Answer 2

Eccentric force

Question 3

What is an eccentric force?

Answer 3

A force applied outside the centre of mass, resulting in angular motion.

Question 4

What is torque?

Answer 4

A measure of the turning/rotational/eccentric force applied to a body

Question 5

Name the 3 axis of rotation

Answer 5

Frontal
Transverse
Longitudinal

Question 6

Where does the longitudinal axis run through?

Answer 6

Runs from the head to the toe through the centre of mass

Question 7

Where does the transverse axis run through?

Answer 7

Runs from the left to right through the centre of mass

Question 8

Where does the longitudinal axis run through?

Answer 8

Runs from front to back through the centre of mass

Question 9

Which movements can occur around the longitudinal axis?
Give 2 examples of sporting actions that turn about the longitudinal axis

Answer 9

Rotation, medial and lateral rotation

Pirouette in ballet / Full twist in trampolining
Turning head to breath in front crawl

Question 10

Which movements can occur around the transverse axis?
Give 2 examples of sporting actions that turn about the transverse axis

Answer 10

Flexion and Extension, dorsiflexion and plantar flexion

Bicep curl
Somersault

Question 11

Which movements can occur around the frontal axis?
Give 2 examples of sporting actions that occur about the frontal axis.

Answer 11

Abduction and adduction

Star jump
Cartwheel

Question 12

What is angular velocity?

Answer 12

The rate of change in angular displacement

Question 13

What is angular velocity measured in?

Answer 13

Radians per second

Question 14

How do you calculate angular velocity?

Answer 14

Angular velocity = angular displacement / time taken

Question 15

What is moment of inertia?

Answer 15

The resistance of a body to change its state of angular motion or rotation

Question 16

How do you calculate moment of inertia?

Answer 16

MOI = mass x distribution of mass from the axis of rotation

Question 17

What is moment of inertia measured in?

Answer 17

kgm squared

Question 18

What two factors effect moment of inertia?

Answer 18

Mass
Distribution of mass from the axis of rotation

Question 19

How does mass effect moment of inertia?

Answer 19

The greater the mass of the body the greater the MOI

Question 20

How does distribution of mass from the axis of rotation affect moment of inertia?

Answer 20

The greater the distribution of mass from the axis of rotation, the greater the MOI

Question 21

Explain how moment of inertia has a direct effect on angular velocity

Answer 21

• If the moment of inertia is high, resistance to rotation is also high, therefore angular velocity is low: the rate of spin in slow
• If the moment of inertia is low, resistance to rotation is also low, therefore angular velocity is high: the rate of spin is fast

Question 22

What is angular momentum?

Answer 22

The quantity of angular motion possessed by a body

Question 23

How do you calculate angular momentum?

Answer 23

Angular momentum = moment of inertia x angular velocity

Question 24

What is angular momentum measured in?

Answer 24

Kgm(squared)rad/s

Question 25

What is meant by the term conservation of angular momentum?

Answer 25

Angular momentum is a conserved quantity that remains constant unless an external eccentric force is applied

Question 26

Describe the angular analogue of Newtons 1st law of motion

Answer 26

A rotating body will continue to turn about its axis of rotation with constant angular momentum unless acted on by an eccentric force.

Question 27

Explain how conservation of angular momentum would be applied for an ice skater doing a triple axel jump

Answer 27

• At the start of the jump, the ice skater applies an eccentric force to begin rotation around the longitudinal axis.
  -Initially their MOI is high as their arms and legs are spread out, taking their distribution of mass away from the axis of rotation. During this point their angular velocity is low.
  -They then bring their arms and legs close to the longitudinal axis, this decreases MOI and increases angular velocity.
  -When they want to slow down, the ice skater takes their arms and legs back out to the sides to once again take their distribution of mass away from the axis of rotation. This increases their MOI, which decreases their angular velocity.
  -During this, angular momentum stays the same, as angular velocity and MOI are inversely proportional, when one increases the other decreases, to keep angular momentum constant.