Introduction
This PSLE Science question tests understanding of elastic spring force and the ability to interpret force–extension/compression graphs.
Students must identify which spring is stiffer, which extension is larger, and how the direction of elastic spring force changes depending on compression or extension.
The teacher uses diagrams and graphs to explain the reasoning clearly.
The Question
Students are shown several spring situations and graphs.
They must determine which diagram correctly represents the elastic spring force acting on an object that is either:
- stretched (extended), or
- compressed
And how the size of the elastic force relates to the stiffness of the spring.
Step-by-Step Explanation (Following Teacher’s Working)
1. Elastic Spring Force (ESF) Always Acts Opposite the Change
- If the spring is extended, ESF pulls back inward.
- If the spring is compressed, ESF pushes outwards.
This is because springs try to return to their original length.
2. More Stiff = Greater Elastic Force
Stiffer springs exert larger ESF for the same amount of extension/compression.
The teacher labels on the board:
- “stiffer → greater force”
- “less stiff → smaller force”
3. Use the Graphs to Compare Elasticity
Graphs show:
- Steeper gradient → more stiff
- Less steep gradient → more elastic
Students must choose the diagram that correctly matches:
- The direction of ESF
- The magnitude of ESF based on stiffness
4. Matching the Correct Diagram
The teacher evaluates all the options and checks:
- Is the force arrow pointing the correct direction?
- Does the arrow length match the spring stiffness?
After elimination, only Option (3) correctly shows:
- Correct direction of elastic spring force
- Correct relative size of the force
✅ Correct Answer: Option (3)
Key Concepts
| Concept | Why It Matters |
| Elastic Spring Force | Springs resist changes in length |
| Direction of ESF | Always opposite extension or compression |
| Stiffness | Determines how large the spring force is |
| Graph Interpretation | Steeper slope = greater resistance |
Tips for Students
✔ Always check the direction of forces first.
✔ Remember: extended → pull, compressed → push.
✔ Use graph slope to tell which spring is stiffer.
✔ Longer force arrow = stronger force.
✔ Draw small diagrams if unsure — just like the teacher did.
For Parents
Elastic force is a foundational PSLE topic.
Understanding how force arrows relate to diagrams and graphs helps students build strong conceptual reasoning.
These skills are essential for Booklet B open-ended sections too.