A2: Angular Motion

Question 1

Definition of angular motion:

Answer 1

Movement of a body in a circular path about an xis of rotation

Question 2

What causes angular motion?

Answer 2

Caused by an eccentric force applied outside the body’s centre of mass

Question 3

Definition of torque:

Answer 3

A measure of turning force applied to a body

Question 4

What are the 3 principal axes of rotation?

Answer 4

Longitudinal
Transverse
Frontal

Question 5

Location of longitudinal axis and sporting example:

Answer 5

Runs from head to toe

E.g. Trampoline performs a full twist turn

Question 6

Location of transverse axis and sporting example:

Answer 6

Runs from side to side

E.g. A front somersault

Question 7

Location of frontal axis and sporting example:

Answer 7

Runs from front to back

E.g. A cartwheel

Question 8

What are the 3 descriptors of angular motion?

Answer 8

Moment of inertia (MI)
Angular velocity (AV)
Angular momentum (AM)

Question 9

Definition of MI

Answer 9

Resistance of a body to change its state of angular motion or rotation

Question 10

Calculation and units for MI

Answer 10

Mass x (Distribution of mass from axis of rotation ^2)
Measured in kgm^2

Question 11

Definition of AV

Answer 11

Rate of change of angular displacement or rate of rotation

Question 12

Calculation and units for AV

Answer 12

Angular displacement / Time taken

Measured in radians/sec

Question 13

Definition of AM

Answer 13

Quantity of angular motion possessed by a body

Question 14

Calculation and units for AM

Answer 14

Product of other two descriptors: AV x MI

Measured in kgm^2/s

Question 15

How does mass affect size of MI of rotating body?

Answer 15

Greater mass = greater MI
Lower mass = easier to change rate of spin
(Diving performed by low mass athletes)

Question 16

How does distribution of mass from axis of rotation affect MI?

Answer 16

Further from axis of rotation = Greater MI

e.g tucked somersault has low MI, greater rate of spin

Question 17

How does MI affect AV?

Answer 17

High MI = Low AV
Low MI = High AV
(resistance to rotation means rate of spin is low)

Question 18

Definition of conservation of angular momentum:

Answer 18

Angular momentum is a conserved quantity so remains constant until an eccentric force or torque is applied

Question 19

Angular analogue of Newton’s First Law:

Answer 19

A rotating body will continue to rotate about its axis of rotation with constant angular momentum unless acted upon by an eccentric force/torque

Question 20

Angular analogue of Newton’s Second Law:

Answer 20

A body’s rate of change in angular momentum is proportional to the size of the eccentric force applied, and acts in the same direction

Question 21

Angular analogue of Newton’s Third Law:

Answer 21

For every force (torque) exerted by a first body on a second body, there will be an equal and opposite force exerted by the second body on the first body