OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Explain that to stretch, bend or compress an object, more than one force…
Full specification wording
Forces in action: explain that to stretch, bend or compress an object, more than one force has to be applied (to include: applications to real life situations)
A single force acting on an object does not stretch, bend or compress it; it simply accelerates the object in the direction of the force.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 7 of 21
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A single force acting on an object does not stretch, bend or compress it; it simply accelerates the object in the direction of the force. To change shape, forces must act in opposing directions so that the object is pulled or pushed from more than one side. Stretching a spring means pulling each end outwards; compressing a spring means pushing each end inwards; bending a beam means applying forces that do not act along the same line. In each case the forces are applied at different points and are not balanced overall in the sense of producing no distortion, so the object deforms. Real-life examples include a gymnast's uneven bars bending under her weight and the reaction at the supports, a bridge deck flexing under traffic, and a rubber band stretched between two fingers.
What earns the marks
- States that a single force produces acceleration rather than a change of shape.
- Identifies that two or more forces act at different points on the object.
- Describes the forces as acting in opposing or non-collinear directions to cause distortion.
- Applies the idea to a named real-life situation such as a stretched spring, bent beam or compressed spring.
Common mistakes and how to put them right
Assumes one force alone can stretch an object.
Put it right by noting that a single force accelerates the object without changing its shape.
Treats the two forces as a balanced pair producing no effect.
Put it right by recognising that forces at different points cause distortion.
Describes only one force in a real-life example.
Put it right by naming both the applied force and the opposing force or reaction.
Exam tips
- Read the question carefully to check whether it asks about stretching, bending or compressing, and match your example to that action.
- Name the object and both forces in any real-life application rather than giving a vague description.
- Remember that the two forces act at different points, not just in opposite directions at the same point.
Try the lesson
The start of the Forces in action: explain that to stretch, bend or compress an object, more than one force has to be applied (to include: applications to real life situations) lesson, made from checked teaching notes for this specification point.
Have a go first
A rubber band is held still and stretched. Why must forces act on it from both ends rather than from one end alone?
Listen
A single force acting on an object does not stretch, bend or compress it; it simply accelerates the object in the direction of the force. To change shape, forces must act in opposing directions so that the object is pulled or pushed from more than one side. Stretching a spring means pulling each end outwards; compressing a spring means pushing each end inwards; bending a beam means applying forces that do not act along the same line. In each case the forces are applied at different points and are not balanced overall in the sense of producing no distortion, so the object deforms. Real-life examples include a gymnast's uneven bars bending under her weight and the reaction at the supports, a bridge deck flexing under traffic, and a rubber band stretched between two fingers. A strong answer earns marks for these points. States that a single force produces acceleration rather than a change of shape. Identifies that two or more forces act at different points on the object. Describes the forces as acting in opposing or non-collinear directions to cause distortion. Applies the idea to a named real-life situation such as a stretched spring, bent beam or compressed spring. A common slip: Assumes one force alone can stretch an object. Instead, noting that a single force accelerates the object without changing its shape. Exam tip: Read the question carefully to check whether it asks about stretching, bending or compressing, and match your example to that action.
See it
Key words
Say what each word means before you turn the card.
Forces and shape change
Try answering aloud or in your head before turning the card.
Opposing forces at different points
Try answering aloud or in your head before turning the card.
Real-life applications of deformation
Try answering aloud or in your head before turning the card.
See every definition
- Forces and shape change
- To stretch, bend or compress an object, more than one force has to be applied, because a single force simply accelerates the object in the direction of the force.
- Opposing forces at different points
- Forces must act in opposing directions at different points so that the object is pulled or pushed from more than one side, and are not balanced overall in the sense of producing no distortion.
- Real-life applications of deformation
- Examples include a gymnast's uneven bars bending under her weight and the reaction at the supports, a bridge deck flexing under traffic, and a rubber band stretched between two fingers.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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