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Moment

Key Stage 3

Meaning

A moment is the turning effect of a force.

About Moments

When a force acts on an object with a pivot it becomes a turning force called a moment.
A moment can be calculated by multiplying a force by the distance from a pivot.
The units of a moment are Newton Metres (Nm).
Moments can be used to make Force Multipliers using a pivot and lever.
The longer the lever, the larger the moment that can be produced.
PivotLever.png
Using moments an effort can be used to lift a load. If the pivot is closer to the load than the effort then the force of effort can be smaller than the load to lift the object.

Equation

Moment = Force x Perpendicular distance from the pivot.

\(M = F \times d\)

Where:

M = Moment
F = Force
d = Perpendicular distance from the pivot.

Example Calculations

A 20N force of effort is applied at a perpendicular distance of 0.15m from the pivot. Calculate the Moment. A 20N force of effort is applied at a perpendicular distance of 14cm from the pivot. Calculate the Moment. A 20N force of effort is applied at a perpendicular distance of 100mm from the pivot. Calculate the Moment.
MomentSpanner1.png
MomentSpanner2.png
MomentSpanner3.png

Force = 20N

Perpendicular distance = 0.15m

\(M = F \times d\)

\(M = 20 \times 0.15\)

\(M = 3.0Nm\)

Force = 20N

Perpendicular distance = 14cm = 0.14m

\(M = F \times d\)

\(M = 20 \times 0.14\)

\(M = 2.8Nm\)

Force = 20N

Perpendicular distance = 100mm = 0.10m

\(M = F \times d\)

\(M = 20 \times 0.10\)

\(M = 2.0Nm\)

Extra Information

Key Stage 4

Meaning

A moment is the turning effect of a force.

About Moments

When a force acts on an object with a pivot it becomes a turning force called a moment.
A moment can be calculated by multiplying a force by the distance from a pivot.
The units of a moment are Newton Metres (Nm).
Moments can be used to make Force Multipliers using a pivot and lever.
The longer the lever, the larger the moment that can be produced.
PivotLever.png
Using moments an effort can be used to lift a load. If the pivot is closer to the load than the effort then the force of effort can be smaller than the load to lift the object.

Equation

Moment = Force x Perpendicular distance from the pivot.

\(M = F \times d\)

Where:

M = Moment
F = Force
d = Perpendicular distance from the pivot.

Example Calculations

A hammer is used to pull out a nail from a wall. A 30N force of effort is applied at a perpendicular distance of 0.18m from the pivot. While the nail is 0.02m away from the pivot. Calculate the force applied to the nail at this point. A hammer is used to pull out a nail from a wall. A 30N force of effort is applied at a perpendicular distance of 19cm from the pivot. While the nail is 4cm away from the pivot. Calculate the force applied to the nail at this point. A hammer is used to pull out a nail from a wall. A 30N force of effort is applied at a perpendicular distance of 200mm from the pivot. While the nail is 60mm away from the pivot. Calculate the force applied to the nail at this point.
MomentHammer1.png
MomentHammer2.png
MomentHammer3.png
A 30N force of effort is applied at a perpendicular distance of 0.18m from the pivot. Calculate the Moment. A 30N force of effort is applied at a perpendicular distance of 19cm from the pivot. Calculate the Moment. A 30N force of effort is applied at a perpendicular distance of 200mm from the pivot. Calculate the Moment.
1. State the known quantities

Force = 30N

Perpendicular distance between effort and pivot = 0.18m

Perpendicular distance between effort and pivot = 0.02m

1. State the known quantities

Force = 30N

Perpendicular distance between effort and pivot = 19cm = 0.19m

Perpendicular distance between effort and pivot = 4cm = 0.04m

1. State the known quantities

Force = 30N

Perpendicular distance between effort and pivot = 200mm = 0.200m

Perpendicular distance between effort and pivot = 60mm = 0.06m

2. Find the moment caused by the effort.

\(M = F \times d\)

\(M = 30 \times 0.18\)

\(M = 5.4Nm\)

2. Find the moment caused by the effort.

\(M = F \times d\)

\(M = 30 \times 0.19\)

\(M = 5.7Nm\)

2. Find the moment caused by the effort.

\(M = F \times d\)

\(M = 30 \times 0.20\)

\(M = 6.0Nm\)

3. Calculate the Force applied to the nail from the moment.

Moment = 5.4Nm

Perpendicular distance = 0.02m

\(M = F \times d\)

\(5.4 = F \times 0.02\)

\(F = \frac{5.4}{0.02}\)

\(F = 270N\)

3. Calculate the Force applied to the nail from the moment.

Moment = 5.7Nm

Perpendicular distance = 4cm = 0.04m

\(M = F \times d\)

\(5.7 = F \times 0.04\)

\(F = \frac{5.7}{0.04}\)

\(F = 142.5N\)

3. Calculate the Force applied to the nail from the moment.

Moment = 6.0Nm

Perpendicular distance = 60mm = 0.06m

\(M = F \times d\)

\(6.0 = F \times 0.06\)

\(F = \frac{6.0}{0.06}\)

\(F = 100N\)

References

AQA

Moment, pages 168-9, GCSE Physics; Student Book, Collins, AQA
Moments, page 57, GCSE Physics; The Revision Guide, CGP, AQA
Moments, pages 120-123, 126-127, GCSE Physics; Third Edition, Oxford University Press, AQA
Moments, pages 165, 166, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA

Edexcel

Moments, page 136, GCSE Physics, Pearson Edexcel
Moments, page 68, GCSE Physics; The Revision Guide, CGP, Edexcel
Moments, pages 211-213, GCSE Physics, CGP, Edexcel

OCR

Moment (turning effect), pages 84-85, Gateway GCSE Physics, Oxford, OCR
Moments, pages 38, 39, Gateway GCSE Physics; The Revision Guide, CGP, OCR