Angular motion

Question 1

Define ‘angular motion’

Answer 1

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

Question 2

What is angular motion measured in?

Answer 2

Radians (360 degrees is 2 radians)

Question 3

How is angular motion created?

Answer 3

An eccentric force (torque) applied to a body outside of its centre of mass

Question 4

Name the three anxious of rotation

Answer 4

Longitudinal, transverse and frontal

Question 5

Describe the longitudinal axis

Answer 5

Through the CoM fro head to toe e.g. pirouette in ballet

Question 6

Describe the transverse axis

Answer 6

Through the centre of mass from left to right e.g. somersault

Question 7

Describe the frontal axis

Answer 7

Through the centre of mass splitting front and back e.g. cartwheel

Question 8

Name the three angular motion descriptors

Answer 8

Angular velocity
Moment of inertia
Angular momentum

Question 9

Define ‘angular distance’

Answer 9

The total angle a body turns from start to finish position when rotating about an axis

Question 10

Define ‘angular displacement’

Answer 10

The smallest angle between the start and finish position of a body rotating about an axis

Question 11

Define ‘angular speed’

Answer 11

The rate of change in angular distance (rad/s)

Question 12

Define ‘angular acceleration’

Answer 12

The rate of change in angular velocity (rad/s/s)

Question 13

Define ‘angular velocity’

Answer 13

Rate of change in angular displacement or rate of rotation

Question 14

What is angular velocity measured in?

Answer 14

rad/s

Question 15

How is angular velocity calculated?

Answer 15

Angular displacement / time

Question 16

Give an example of angular velocity

Answer 16

Trampolinist doing a seat drop, flexes their hips so that their legs rate clockwise about the transverse axis 1.5 radians in 0.5s = 3.14 rad/s

Question 17

Define ‘moment of inertia’

Answer 17

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

Question 18

What is moment of inertia measured in?

Answer 18

kilograms per metre squared

Question 19

When is moment of inertia the greatest?

Answer 19

When the mass is further away from the axis of rotation

Question 20

When is moment of inertia the lowest?

Answer 20

Resistance is lower increasing the speed of rotation reduces moment of inertia due to lower resistance e.g. tucked somersault

Question 21

Which leg of a runner has the greatest moment of inertia?

Answer 21

The drive leg has the greatest moment of inertia because the back leg is straight and so has more resistance but the drive leg is closer to the axis of rotation (hip)

Question 22

If moment of inertia is high, resistance to rotation is (1) so angular (2) is low and the rate of (3) is slow

Answer 22

1 - high
2 - velocity
3 - spin

Question 23

Define ‘angular momentum’

Answer 23

The quantity of angular motion possessed by a body

Question 24

What is angular momentum measured in?

Answer 24

kgm(2)rad/s

Question 25

What is the formula of angular momentum?

Answer 25

moment of inertia x angular velocity

Question 26

How is angular momentum created?

Answer 26

To start rotating around an axis angular momentum is required, an eccentric force is needed outside of the centre of mass e.g. a diver jumps from the diving board and leans to ensure the reaction force passes outside of their CoM to create an eccentric force and angular momentum

Question 27

How does Newton's first law apply to angular momentum?

Answer 27

A rotating body will continue to rotate about an axis with constant angular momentum unless acted upon by an external torque

Question 28

What is the importance of angular momentum in take off?

Answer 28

Once in flight, angular momentum cannot be changed and so as much should be generated as possible, once generated moment of inertia can be manipulated e.g. adding complex twists and turns in figure skating to gain points

Question 29

What angular forces are acting on a figure skater at take off?

Answer 29

Skater applies an eccentric force from the ice, their mass is distributed and is away from the longitudinal axis as their arms and legs are away from their midline, moment of inertia is high so angular velocity is low, they are rotating slowly

Question 30

What angular forces are acting on a figure skating mid-flight when spinning in the air?

Answer 30

Their mass is directed towards their longitudinal axis as their arms and legs move towards the midline of their body, MI is lows AV is high so they rotate quickly

Question 31

What angular forces are acting on a body in the landing?

Answer 31

Mass is distributed away from their longitudinal axis as arms and legs are abducted enabling them to have more control of their landing as resistance to rotation increases thus increasing MI and decreasing AV