Introduction

This PSLE Science question tests your understanding of energy conversion when an object falls from a height.
A common mistake is assuming gravitational potential energy changes directly into sound energy before the ball hits the ground — but this is incorrect.

The teacher shows the correct reasoning step-by-step.

The Question

A rubber ball falls and reaches a lower height after bouncing.
The diagram shows the moment when the ball is just about to hit the ground.

What was the energy conversion at this moment?

Options include combinations of:

• Gravitational Potential Energy (GPE) 
• Kinetic Energy (KE) 
• Sound Energy 

Step-by-Step Explanation (Following the Teacher’s Working)

1. At the top, the ball has maximum GPE

Because it is at its highest point relative to the ground.

2. As the ball falls, GPE decreases

The ball is losing height, so GPE decreases.

3. As GPE decreases, Kinetic Energy increases

The ball speeds up as it falls.

So the correct ongoing conversion is:

GPE → Kinetic Energy

4. Sound energy is NOT produced yet

Sound is only produced when the ball hits the ground, not before.

Since the question asks about the moment just before the ball touches the ground:

✔ No sound energy yet
✔ Only GPE being converted to KE

Final Answer

Option (3): GPE → Kinetic Energy

(The only possible correct option.)

Key Concepts

Tips for Students

✔ Energy always transfers, not disappears
✔ When falling → GPE decreases, KE increases
✔ Sound is produced upon impact, not mid-air
✔ Focus on when the event happens (timing is key!)

For Parents

This is a classic PSLE Science topic involving:

• Energy 
• Motion 
• Real-world physical changes 

Questions often require precise understanding of when certain forms of energy appear.
Mastering these ideas is essential for higher-order PSLE questions.