 # Moment

In this worksheet, students will be introduced to the principle of moments and understand what turning forces are. Key stage:  KS 3

Curriculum topic:   Physics: Motion and Forces

Curriculum subtopic:   Motion and Forces

Difficulty level:   ### QUESTION 1 of 10

In the picture, a girl is watching her dad fix her bicycle tyre using a spanner. The spanner exerts a turning force on the axle nut and if the force is big enough, it can unscrew the nut. Turning forces work on a pivot (see diagram). When the weights of the orange and blue blocks are equal (equal forces) and the green block rests on the red pivot at exactly half its length, then the green block, with orange and blue squares on, balances on the pivot. However, if we were to take one of the squares off the green rectangle, the forces would turn it to the other side. For example, if we take the blue square away, then the weight of the orange one would not be balanced, so the green block would turn towards the orange block. The effect of the force depends on the distance from the pivot. The effect is called moment. The moment of a turning force is given by the following formula:

moment  =  force applied  ×  distance from a pivot

Moment is measured in newton centimetres (Ncm) or newton metres (Nm). In order to increase the effect of a turning force, one can either increase the force itself by pulling or pushing harder, or can increase the distance from the pivot.

The cartoon shows a see-saw that is balanced, because of the way a family have sat on it. The total moment of the people sitting on the right side is equal to the total moment of the people sitting on the left side:

total clockwise moment  =  total anticlockwise moment

What type of force does a spanner exert on a bicycle tyre axle nut?

Where do turning forces work?

on a pivot

on a level

on a surface

What is the effect of a turning force called?

Tick one factor that affects the moment of a force.

height from ground

force

movement

Tick another factor that affects the moment of a force.

the height of the person applying the force

distance from pivot

distance from ground

Tick the correct unit of measurement for moment.

Ns

Ncm

Nhr

Tick another correct unit of measurement for moment.

Nm

Nc

Nhr

Calculate the moment of a 5 N force that is applied at 2 cm from the pivot.

2.5 Ncm

10 Ncm

10 Nm

Calculate the moment of a 10 N force that is applied at 20 m from the pivot.

2 Nm

200 Ncm

200 Nm

A brother and sister play on a see-saw as seen in the cartoon. What are the conditions needed to balance the see-saw? total clockwise moment = total anticlockwise moment

total clockwise moment > total anticlockwise moment

total clockwise moment < total anticlockwise moment

• Question 1

What type of force does a spanner exert on a bicycle tyre axle nut?

turning
turning force
EDDIE SAYS
A spanner exerts a turning force on a bicycle tyre axle nut.
• Question 2

Where do turning forces work?

on a pivot
EDDIE SAYS
Turning forces work on a pivot.
• Question 3

What is the effect of a turning force called?

moment
EDDIE SAYS
The effect of a turning force is called moment.
• Question 4

Tick one factor that affects the moment of a force.

force
EDDIE SAYS
The moment of a force depends on the force itself.
• Question 5

Tick another factor that affects the moment of a force.

distance from pivot
EDDIE SAYS
The moment of a force depends on the force itself and the distance from the pivot.
• Question 6

Tick the correct unit of measurement for moment.

Ncm
EDDIE SAYS
Moment is measured in Ncm.
• Question 7

Tick another correct unit of measurement for moment.

Nm
EDDIE SAYS
Moment is measured in Nm as well as Ncm, as seen in the previous question.
• Question 8

Calculate the moment of a 5 N force that is applied at 2 cm from the pivot.

10 Ncm
EDDIE SAYS
moment = force × distance = 5 × 2 = 10 Ncm.
The answer must be in Ncm, because the distance is given in cm.
• Question 9

Calculate the moment of a 10 N force that is applied at 20 m from the pivot.

200 Nm
EDDIE SAYS
moment = force × distance = 10 × 20 = 200 Nm.
The answer must be in Nm, because the distance is given in m.
• Question 10

A brother and sister play on a see-saw as seen in the cartoon. What are the conditions needed to balance the see-saw? total clockwise moment = total anticlockwise moment
EDDIE SAYS
In order for the see-saw to balance, the total clockwise moment must be equal to the total anticlockwise moment.
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