Lesson focus: ElasticAble to go back to its original shape and size when the force is taken away, like a rubber band., stiff and strong describe different responses to forceA push or a pull, measured in newtons (N)..
Distinguish reversible and permanent deformationWhen an object stays bent or stretched after the force is taken away. from evidenceObservations or measurements used to show whether an idea is right or wrong..
Build on earlier learning
Introduction to forcesApply force arrows to shape changes caused by interactions.
Practical
Stretching a spring
- Measure the original length of the spring.
- Add 1 N weights one at a time and measure the new length each time.
- Extension = new length − original length.
- Use the model on this page to see where the spring stops returning to its original length.
Record: A force–extension table and graph.
Safety: Wear eye protection; do not stand with feet under the weights.
Stretching a spring
Add weights one newton at a time and watch the extension. Remove them all to test whether the spring returns to its original length.
Controls
Illustrative spring: 4 cm per newton up to 5 N; it stays stretched if loaded beyond 6 N.
You will be successful when you can…
- Describe stretching and compression.
- Identify elastic recovery.
- Distinguish stiffness from strength.
- Recognise permanent deformation.
Words that carry the science
- elastic deformation
- Shape change reversed when force is removed.
- permanent deformation
- Shape change remaining after unloading.
- stiffness
- Resistance to deformation under force.
- strength
- Ability to withstand force without failure.
- compression
- Forces pushing inward and shortening or squashing.
Judge properties from load–unload evidence
01Load and unload
Stretching pulls outward; compressionSquashing something by pushing on it from both ends. pushes inward. Recovery after unloading is the evidence for elasticity.
Here is how to judge a spring. StiffHard to bend or stretch; a stiff spring needs a big force to stretch it a little. means it stretches only a little when you pull it. ElasticAble to go back to its original shape and size when the force is taken away, like a rubber band. means it goes back to its starting length when you let go. If it stays longer after you let go, it has been permanently deformedStretched or bent so much that it stays out of shape when the force is removed. (its shape has changed for good).
02Three properties
A stiff object extends little; an elastic object recovers; a strong object withstands large force. One object can have different combinations.
03Beyond recovery
If a load exceeds the elastic range, structure may rearrange permanently or fail.
Classify two bands
At 10 N, A extends 2 mm and B extends 12 mm. Both return to their original length.
- Both recover, so both are elastic under 10 N.
- A has smaller extension at the same force.
- Therefore A is stiffer.
- No breaking data are given, so strengthHow much force something can take before it breaks. cannot be compared.
How to make the reasoning visible: Use only the property supported by the measurements.
Load–unload evidence
Original length is 10.0 cm.
| Object | Loaded length | Unloaded length | Conclusion |
|---|---|---|---|
| A | 11.0 cm | 10.0 cm | Elastic; 1.0 cm extension |
| B | 13.0 cm | 10.0 cm | Elastic; less stiff than A |
| C | 12.0 cm | 10.6 cm | Permanent deformation |
| D | 10.4 cm | 10.0 cm | Elastic and stiffest here |
Which object is stiffest under the test force?
Which has permanent deformation?
Use the table. Why is object C showing permanent deformation?
Check your understanding
Answer from memory, then check against the suggested answer.
What is elastic deformation?
What is permanent deformation?
What is stiffness?
What is compression?
Give an example of an object that deforms elastically.
A climbing rope stretches but returns. Which useful property is shown?
Can glass be stiff but not tough?
Why is a car seat spring made to deform elastically and not permanently?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Two springs are pulled with the same force. Spring X stretches 2 cm and goes back to its starting length. Spring Y stretches 5 cm and stays 1 cm longer after the force is removed. Answer the parts to compare them.
Which spring is stiffer (stretches less)? Give the evidence.
(1)Which spring is elastic? Give the evidence.
(1)Spring Y stretches more. What does this tell you about how stiff Y is?
(1)Spring Y stays 1 cm longer. What has happened to it?
(1)Total for this question: 4 marks
Command word: For compareA command word: say how two or more things are similar and how they are different., say something about both springs. Use the numbers, then name the property.