Friction can cause energy to dissipate (spread out and become unusable) into the surroundings, causing them to heat up.

Efficiency is the fraction of energy supplied to an object or system that is usefully transferred by it.

The amount of energy usefully transferred by an object or system is the useful energy transferred by the device.

The total amount of energy transferred to an object or system is the total energy supplied to the device.

Efficiency (in terms of useful energy transferred)

Combined science

In the Forces make things change unit, they will build on this knowledge to learn how to combine forces in two dimensions, how to calculate acceleration from a resultant force and how to calculate forces in collisions and explosions.

In the Measuring and calculating motion unit, pupils learnt how to measure and calculate velocity and acceleration, and how to interpret displacement-time and velocity-time graphs. 

Energy of moving objects

Physical activity and equipment requiring safe use

40 J in the gravitational store and 10 J in the thermal store.

40 J in the gravitational store and 20 J in the thermal store.

40 J in the gravitational store and 30 J in the thermal store.

A ball has 50 J of energy in the gravitational store and 20 J in the thermal store.
Which of the following could be the amount of energy in each store after the ball has been dropped and rebounded?  

Energy is {{}} when it is transferred to the thermal store of the surroundings.

The amount of energy that makes something useful happen.

The fraction of the energy supplied that makes something useful happen.

The fraction of the energy supplied that dissipates.

Which of the following is a correct definition for efficiency?

Aisha is investigating how the temperature of a tennis ball affects its rebound height.
Match up the variable on the left to the type of variable for this experiment on the right.

efficiency = useful energy transferred + total energy supplied

efficiency = useful energy transferred – total energy supplied 

efficiency = useful energy transferred × total energy supplied 

efficiency = useful energy transferred ÷ total energy supplied 

Which of the following is the correct equation for efficiency?

A forklift truck transfers 24 000 J of energy when lifting a box onto a high shelf.
Calculate the efficiency of the truck if 18 000 J of energy is transferred to the gravitational store. 

Which of the following forces slow down a sledge that is sliding down a snow-covered hill?

Which of the energy stores does friction transfer energy into?

energy due to an object's mass and height

Match the energy stores on the left to their descriptions on the right. 

All of its energy is transferred to the surroundings.

Some of its energy is transferred to the surroundings.

Earth's gravitational force is pulling the ball downwards.

The normal reaction force from the ground is less than the gravitational force.

Pushing air out of the way uses up some of the ball's energy.

Pushing air out of the way transfers some energy to the air particles.

Why is the rebound height of a ball not the same as the height that it was dropped from?

The law of conservation or energy states that energy cannot be created or ...

Content guidance

Risk assessment required - equipment

Adult supervision required

Starter Quiz