Six forms of energy: kinetic, potential, light, electrical, sound, heat. Energy is derived ultimately from the Sun. Energy can be converted from one form to another.
energy formsenergy conversionconservation
6 forms of energy — definitions & examples
Kinetic energy
Energy of a moving object e.g. rolling ball, moving car
Potential energy
Stored energy (position/stretched) e.g. raised object, stretched elastic
Light energy
Energy that enables us to see e.g. Sun, bulb, torch
Heat energy
Energy that makes things warm e.g. fire, friction, hot water
Electrical energy
Energy carried by electric current e.g. battery, mains electricity
Sound energy
Energy from vibrations e.g. speaker, drum, voice
Common conversions to know
Electrical
→
Light + Heat
(light bulb)
Electrical
→
Sound + Heat
(speaker)
Potential
→
Kinetic
(falling object, ball rolling downhill)
Kinetic
→
Heat + Sound
(friction, braking)
Light
→
Electrical
(solar panel)
Key principle: Energy is never created or destroyed — it is converted from one form to another. The Sun is the original source of most energy on Earth.
Part A — Multiple choice (Booklet A style · 2 marks each)
Question 1 — MCQ (2 marks)
Booklet AIdentifying energy forms
A student stretches a rubber band and releases it, sending a paper ball flying across the room. It then lands on the floor with a soft thud. Which sequence of energy conversions is correct?
AKinetic → Potential → Sound
BElectrical → Kinetic → Sound
CPotential → Kinetic → Sound
DKinetic → Potential → Heat
The stretched rubber band stores potential energy. When released, it converts to kinetic energy as the paper ball moves. The thud on landing produces sound energy. Potential → Kinetic → Sound.
Question 2 — MCQ (2 marks)
Booklet ASun as energy source
Which statement about energy resources is correct?
ACoal is a renewable energy resource because it can be found underground.
BSolar panels convert electrical energy into light energy.
CThe Sun gets its energy from coal buried deep inside it.
DMost of our energy resources are derived in some way from the Sun.
D is the key syllabus statement. Coal (fossil fuel) formed from ancient plants that captured the Sun's energy — so even coal's energy originates from the Sun. Solar panels convert light → electrical (not the reverse). Coal is non-renewable as it takes millions of years to form.
The diagram shows a wind-up toy car. A key is used to wind a spring inside the car. When released, the car moves forward and makes a whirring noise. The axle also gets slightly warm from friction.
(a) What form of energy is stored in the wound-up spring? (1 mark)
(b) When the car is released, the stored energy converts into three forms. Name all three. (2 marks)
(a)Potential energy — the compressed/wound spring stores energy due to its stretched/compressed state.
(b)The three forms produced are:
Kinetic energy — the car moves forward
Sound energy — the whirring noise
Heat energy — the axle gets warm due to friction
Potential → Kinetic + Sound + Heat
Most energy conversions in real life produce heat as a "waste" product due to friction. Heat from friction is very commonly tested in PSLE energy questions — always check whether friction is mentioned and add heat energy to your answer.
A student rolls a ball from different heights down a ramp onto a flat surface. A wooden block is placed at the bottom. She measures how far the block moves after being hit. The table shows her results.
(a) Using energy terms, explain why a ball released from a greater height causes the block to move further. (2 marks)
(b) State one variable that must be kept the same in this investigation for it to be a fair test. (1 mark)
(c) The student repeats Trial 2 but replaces the ball with a heavier ball of the same size, released from 20 cm. Predict whether the block will move more or less than 12 cm. Explain your answer. (1 mark)
(a)A ball at a greater height has more potential energy. When released, this potential energy converts to kinetic energy as the ball rolls down. The greater the height, the more kinetic energy the ball has when it reaches the bottom — so it hits the block with more force and pushes it further.
(b)Accept any one: the same ball (same mass and size) / the same ramp (same surface) / the same starting position of the block / the same type of surface on the floor.
(c)The block will move more than 12 cm. A heavier ball at the same height stores more potential energy, which converts to more kinetic energy at the bottom — hitting the block with greater force and pushing it further.
Higher → more PE → more KE at bottom → block moves further
For (a), don't just say "the ball has more energy." Name the specific forms: potential energy at the top, kinetic energy at the bottom, and explain the conversion. Two named energy forms + the conversion = full marks.
The diagram shows a hydroelectric dam. Water stored in a reservoir behind the dam is released and flows downhill through pipes. The moving water spins a turbine, which drives a generator to produce electricity. The electricity powers homes and factories.
(a) Name the form of energy stored in the water in the reservoir. (1 mark)
(b) Trace the complete energy conversion pathway from the reservoir to the homes. Name each form of energy at each stage. (2 marks)
(c) In homes, the electrical energy is used to power a television. State two forms of energy that the television converts electrical energy into. (1 mark)
(d) A student says: "We should always use hydroelectric power instead of burning coal, because hydroelectric power creates energy from nothing." Identify the scientific error in this statement and correct it. (1 mark)
(a)Potential energy — the water is stored at a height above the turbines.
(b)Potential energy (reservoir) → Kinetic energy (moving water flowing downhill) → Electrical energy (generated by the turbine/generator) → electrical energy reaches homes.
(c)Light energy (the screen) and Sound energy (the speakers). Heat energy is also produced as a by-product but is not the intended output.
(d)The error is "creates energy from nothing." Energy cannot be created — it can only be converted from one form to another. Hydroelectric power converts the potential energy of stored water (which originally came from the Sun via the water cycle) into electrical energy.
PE → KE → Electrical → Light + Sound (+ heat)
Part (d) tests the most important energy principle: energy is never created or destroyed, only converted. "Creating energy from nothing" is always scientifically wrong. Any question asking you to evaluate a claim about energy should check whether this principle is being violated.
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