Distinguish mechanical and electrical energy transfers
Use forces and currents to describe transfers without calling work an energy store.
Exam scope and assessment notes
Core and Extended · Physics 0625, 2026–2028, section 1.7.1. Energy stores, transfers and simple conservation are Core; kinetic and gravitational potential energy equations, multistage conservation and Sankey diagrams are Supplement. State the system, interval and model assumptions. Written practice is self-checked. Supervised practical experience, cumulative assessment and human subject-teacher review remain pending.
Before you begin
- Distinguish energy stores from pathways.
- Describe a force and the motion it acts through.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which description includes a force acting through movement?
What you will learn
- Recognise transfer by forces as mechanical work.
- Recognise transfer by electric currents as electrical work.
Forces can transfer energy by mechanical work
A force acting through a distance can transfer energy mechanically. A person lifting a load transfers energy that increases the load–Earth gravitational potential store. Friction during sliding can transfer energy from a kinetic store to internal stores of the interacting objects and surroundings. Mechanical work is the transfer, not an eighth store added to the seven-store list.
The direction and movement matter: holding an ideal stationary load does not transfer mechanical energy to that load through displacement, even though a person expends chemical energy internally. Do not identify a force's existence alone with mechanical work done on the selected object. The adjoining Work pathway quantifies aligned force and distance.
A current can transfer energy electrically
A battery can transfer energy electrically through a current to a motor or heater. The battery's chemical store decreases; a motor may increase a load's kinetic or gravitational potential store, while a heater increases internal energy in itself and nearby material. A wire or current is the electrical pathway in this description rather than the final store in the warmed water.
A sequence can contain both transfers: a battery transfers energy electrically to a motor, and the motor transfers energy mechanically to a load. Intermediate components can gain internal energy. Name the pathway at each stage instead of treating 'electrical energy' as a complete account that identifies every source and destination.
Pause and explain
Can the same lift involve electrical and mechanical transfer at different stages?
Worked example
Describe the transfer pathways from a battery through a motor to a lifted load.
Show the worked solution
- The battery supplies energy electrically through a current to the motor.
- The motor transfers energy mechanically to the load through a force acting during motion.
- The load–Earth gravitational potential store increases, with other internal-store gains possible.
Answer Electrical transfer to the motor, then mechanical transfer to the load.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Name pathways from a battery to a motor and from the motor to a moving load.
Give me a hint
Identify the interaction at each stage.
Compare my reasoning
- The current gives an electrical transfer to the motor.
- The pulling force acts through the load's displacement.
- The second stage is mechanical work.
Electrical to motor; mechanical to load.
Look for these in your work
- Name both stages.
- Distinguish pathways from destination stores.
Classify a current heating a wire and friction slowing a sliding block.
Give me a hint
Look for a current in one case and a force through distance in the other.
Compare my reasoning
- The wire receives energy electrically.
- Friction transfers energy mechanically from the block's kinetic store.
- Internal stores increase in the interacting materials and surroundings.
Electrical transfer to the wire; mechanical transfer during sliding friction.
Look for these in your work
- Use the specified interactions.
- Include an internal-store destination.
A student says holding an ideal motionless load necessarily does mechanical work on that load because the support force is large. Explain the limitation.
Give me a hint
Separate displacement of the load from energy use inside the person.
Compare my reasoning
- Mechanical work on the selected load needs relevant displacement.
- The ideal load's displacement is zero.
- The person can still expend chemical energy internally without the proposed mechanical transfer to that stationary load.
No displacement means no mechanical work on this ideal stationary load; internal bodily energy use is a different account.
Look for these in your work
- Identify the selected object.
- Do not equate force magnitude alone with transfer.
Common mistakes
- Work describes a transfer.
- A force without relevant displacement does not establish mechanical work on that object.
- Name both pathways in a motor-driven lift.
What can you explain now?
What pathway transfers energy from a current to a heater?
Compare with the explanation
Electrical work.
The current transfers energy electrically; the heater's internal store can increase.
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Make it stick
Explain mechanical and electrical work using a motor lift and distinguish holding a stationary load from lifting it.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.