Energy forms and transfer
Key idea: Devices transfer energy from one form or store to others. Thermal energy transfers from hotter objects to cooler ones until they reach the same temperature.
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Guided lessons · coming soon
Guided lesson
Guided steps
- Follow the lamp’s input and outputs, then compare temperatures.
- Identify the direction of energy transfer as the drink cools.
- Correct the claim that cold flows into the drink.
- Name the battery toy’s starting store and every observed output.
- Follow the energy from the spring to every observed output.
- Use the observations to identify useful and other outputs.
- Compare the phone and air temperatures to find the transfer direction.
- Follow the energy from the raised car as it rolls.
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ContinueEnergy is never used up: it is transferred from one store or form to others. To describe what a device does, name the energy it takes in and every form it gives out.
Energy forms and transfers
The energy forms you need are electrical, kinetic, light, sound and thermal energy, and chemical, elastic and gravitational potential energy. A lamp, for example, takes in electrical energy and gives out light and thermal energy. Name the form at the start and every form at the end, rather than saying the energy is used up.
When two objects are at different temperatures, energy is transferred thermally from the hotter one to the cooler one. A hot drink in a cooler room transfers energy to the room, more and more slowly, until both are at the same temperature. They have then reached thermal equilibrium. Cold is not something that flows into the drink.
Worked example 1
Cooling drink
Problem
A drink at 65 °C is placed in a room at 25 °C. Predict the net thermal transfer.
Show full solution
Reason from the evidence
Method
Compare the two temperatures and name the hotter and cooler regions.
Reason
Energy transfers from hotter to cooler regions; ‘cold’ does not flow into the hot object.
Working
Answer
- Compare the two temperatures.
Thermal energy transfers from the higher-temperature drink to the lower-temperature surroundings.
- Net transfer continues until both reach thermal equilibrium.
State the conclusion
Working
Answer
The net transfer is from the drink to the surroundings; ‘cold’ does not flow into the drink.
Quick check
Spot the mistake 2
Does cold flow into the drink?
Learner response
“The drink cools because cold flows into it from the room.” Locate the first scientific error and replace it.
Explain the direction of the transfer
Show solution step by step
Identify what actually transfers
Method
Replace “cold flows” with a statement about thermal-energy transfer.
Reason
Cold is not a substance or energy form that moves into an object.
Working
Answer
Thermal energy transfers from the hotter drink to the cooler surroundings.
Use the temperature condition
Reason
Net transfer continues only while a temperature difference remains.
Working
Answer
The drink cools until it reaches the same temperature as its surroundings.
Common mistake
Guided practice 3
Describe the energy transfers
Problem
A battery-powered toy car moves, makes sound and becomes slightly warm. Describe the energy transfers.
Work through the steps
Hints
Hint 1
name the input form
Name the input form.
Hint 2
list every observed output, including the surroundings
List every observed output, including the surroundings.
Show full solution
Answer
Working
Answer
Chemical energy in the battery is transferred electrically, then mainly into kinetic, sound and thermal energy.
Quick check
The thermal output still counts even though it is not the toy’s intended job.
Try it yourself 4
Follow the energy in a wind-up toy
Problem
A wound spring drives a toy without a battery or electric motor. The toy moves, makes sound and becomes slightly warm. Describe the energy transfers from the wound spring and explain whether electrical energy belongs in it.
Account for every observed output
Hints
Hint 1
start at the spring
Which energy store belongs to a deformed spring?
Hint 2
use every observation
Movement, sound and warming each reveal an output transfer.
Show solution step by step
Name the input and useful output
Method
Begin with the spring’s stored energy and connect it to the moving toy.
Reason
The unwinding spring drives the toy mechanically; no electric motor is involved.
Working
Answer
elastic potential energy → kinetic energyComplete the account
Method
Add the sound and thermal outputs.Reason
The observations show that not all the transferred energy becomes useful movement.
Working
Answer
Some energy is also transferred as sound and thermally to the toy and surroundings. There is no electrical transfer: the spring drives the mechanism directly.
Quick check
Observing energy transfers
Run a battery-powered toy at one setting for 30 seconds and record every output you can see, hear or feel: movement, light, sound, and warming of the motor casing after it is switched off. Repeat twice under the same conditions. Name the energy input, chemical energy in the batteries, and sort the outputs into the toy’s intended useful output and the others. Use only low-voltage battery devices, and stop if anything becomes unusually hot.
| Trial | Useful output | Other outputs |
|---|---|---|
| 1 | motion (kinetic) | sound; warm motor casing (thermal) |
| 2 | motion (kinetic) | sound; warm motor casing (thermal) |
| 3 | motion (kinetic) | sound; warm motor casing (thermal) |
These sample observations name the outputs but do not measure them, so they cannot give an efficiency.
Check your understanding 1 Evidence for a thermal transfer
What temperature measurements would support net thermal-energy transfer from a charging phone to its cooler surroundings? Use measurements from your teacher or a teacher-approved demonstration; do not open a charger or use touch to test hot equipment.
Show answer
A measured casing temperature above the surrounding air temperature supports the hotter-to-cooler direction. Warming of nearby air, with other heating conditions kept the same, provides further evidence of transfer to the surroundings. A rise in the casing temperature alone tells you the phone is warming. Compare its temperature with the air to find the direction of net transfer.
Check your understanding 2 A different starting store
A toy car is released from rest at the top of a ramp. It has no battery or wound spring. It rolls downhill and makes sound as it moves. Name the starting energy store and describe where energy transfers as the car moves, including a possible thermal transfer.
Show answer
The raised car has gravitational potential energy. As it descends, energy transfers to kinetic energy of the moving car, sound and thermal energy in the car, ramp and surroundings. The car starts with energy stored by its raised position, rather than in a battery or spring. Include sound and warming as well as motion.
Common mistakes
- Saying energy is used up, instead of naming the forms it is transferred to.
- Leaving out an output, such as sound or thermal energy.
- Saying cold flows into a cooling object. Energy flows out of the hotter object.
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Syllabus and review details
- SEC G1 Science 2027 · 2027
Content structure and syllabus content, PDF pages 8–17
Last reviewed: