AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
So a force does work on an object when the force causes a displacement of…
Full specification wording
Work done and energy transfer: So a force does work on an object when the force causes a displacement of the object.
The word displacement is doing real work in this sentence: what counts is how far the object moves in the direction the force acts, not how far it travels altogether.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 2 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The word displacement is doing real work in this sentence: what counts is how far the object moves in the direction the force acts, not how far it travels altogether. A porter walking along a level corridor with a suitcase exerts an upward force while the case moves sideways, so force and displacement are at right angles and no work is done against the weight. A normal contact force transfers no energy when motion is perpendicular to it, but it does work if the surface moves in the direction of the force, like an ascending lift floor. Where force and displacement point the same way, energy flows into the object; where they point opposite ways, as with friction on a sliding box, energy flows out of its kinetic store instead.
What earns the marks
- Linking the force to a displacement in the direction of that force.
- Stating that a force at right angles to the motion does no work.
- Energy transferred to the object when force and displacement are in the same direction.
- A force opposing the motion removing energy from the object.
Common mistakes and how to put them right
Treating any movement as work, including motion at right angles to the force such as a load carried on the level.
Saying the normal contact force from the ground does work on a walker moving horizontally.
Ignoring that friction acts in the opposite sense and so empties the kinetic store.
Using the length of a curved path rather than the displacement in the direction of the force.
Exam tips
- Draw the force arrow and the movement arrow; if they are perpendicular the work is zero.
- If the force opposes the motion, say that the kinetic store falls - that link is usually the mark.
Try the lesson
The start of the Work done and energy transfer: So a force does work on an object when the force causes a displacement of the object. lesson, made from checked teaching notes for this specification point.
Have a go first
A pupil pushes a heavy box, but the box does not move at all. Which statement describes whether work is done on the box by the pupil's push?
Listen
The word displacement is doing real work in this sentence: what counts is how far the object moves in the direction the force acts, not how far it travels altogether. A porter walking along a level corridor with a suitcase exerts an upward force while the case moves sideways, so force and displacement are at right angles and no work is done against the weight. A normal contact force transfers no energy when motion is perpendicular to it, but it does work if the surface moves in the direction of the force, like an ascending lift floor. Where force and displacement point the same way, energy flows into the object; where they point opposite ways, as with friction on a sliding box, energy flows out of its kinetic store instead. A strong answer earns marks for these points. linking the force to a displacement in the direction of that force. stating that a force at right angles to the motion does no work. energy transferred to the object when force and displacement are in the same direction. a force opposing the motion removing energy from the object. Exam tip: Draw the force arrow and the movement arrow; if they are perpendicular the work is zero.
Key words
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displacement in the direction of a force
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perpendicular forces do no work
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friction removing energy
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direction of transfer
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See every definition
- displacement in the direction of a force
- What counts is how far the object moves in the direction the force acts, not how far it travels altogether.
- perpendicular forces do no work
- A force at right angles to the motion does no work, so a normal contact force transfers no energy when motion is perpendicular to it.
- friction removing energy
- Where force and displacement point opposite ways, as with friction on a sliding box, energy flows out of its kinetic store instead.
- direction of transfer
- Where force and displacement point the same way, energy flows into the object; where they point opposite ways, energy flows out of its kinetic store.
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