Students should be able to describe all the changes involved in the way…

The idea

Five standard situations come up again and again. An object projected upwards: kinetic store empties as the gravitational potential store fills, with some energy passing to the thermal store of the surroundings through air resistance. A moving object hitting an obstacle: kinetic store empties, mostly into thermal stores, with some transferred by sound waves. An object accelerated by a constant force: a force does work, filling the kinetic store. A vehicle slowing down: brakes do work against friction, filling the thermal store of the brakes, which is why they get hot. Water boiling in a kettle: the mains does electrical work, filling the thermal store of the water and of the kettle itself.

What earns the marks

• Naming the store that empties and the store that fills for the situation given.
• Naming the pathway, such as work done by a force, electrical working or heating.
• Including the transfer to the thermal store of the surroundings where friction or air resistance acts.
• A statement that the total energy is unchanged across the change described.

Common mistakes and how to put them right

• Saying the kinetic energy is destroyed in a collision rather than transferred to thermal stores and sound.

• Forgetting that a kettle also heats its own element and body, not only the water.

• Using the phrase movement energy or heat energy instead of the kinetic store and the thermal store.

• Leaving out air resistance for a projected object, so the gravitational store is said to gain everything the kinetic store lost.

Exam tips

• Write the change as a chain: store, pathway, store, then add where energy is dissipated.
• Say which object holds the store, because the thermal store of the brakes is not the thermal store of the road.
• A one-mark answer still needs both ends of the transfer, so never name a single store on its own.