Starter quiz
- Which of the following forces slow down a sledge that is sliding down a snow-covered hill?
- air resistance ✓
- friction ✓
- gravitational
- normal reaction force
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- Which of the energy stores does friction transfer energy into?
- chemical store
- gravitational store
- kinetic store
- thermal store ✓
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- Match the energy stores on the left to their descriptions on the right.
- chemical store⇔energy due to chemical reactions ✓
- gravitational store⇔energy due to an object's mass and height ✓
- kinetic store⇔energy due to an object's mass and speed ✓
- thermal store⇔energy due to particle movement ✓
- Why does a hot cup of tea cool down?
- All of its energy is used up.
- All of its energy is transferred to the surroundings.
- Some of its energy is used up.
- Some of its energy is transferred to the surroundings. ✓
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- Why is the rebound height of a ball not the same as the height that it was dropped from?
- 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. ✓
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- The law of conservation or energy states that energy cannot be created or ...
- 'destroyed' ✓
Exit quiz
- 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?
- 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. ✓
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- Energy is ______ when it is transferred to the thermal store of the surroundings.
- 'dissipated' ✓
- Which of the following is a correct definition for efficiency?
- The amount of energy that makes something useful happen.
- The amount of energy that dissipates.
- The fraction of the energy supplied that makes something useful happen. ✓
- The fraction of the energy supplied that dissipates.
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- 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.
- temperature of the ball⇔independent variable ✓
- rebound height of the ball⇔dependent variable ✓
- height that the ball is dropped from⇔control variable ✓
- Which of the following is the correct equation for efficiency?
- 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 ✓
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- 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.
- 0.75 ✓
- 1.33
- 6000 J
- 18 000 J
- 0.75 J
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Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- Energy is dissipated due to friction which causes particles to vibrate more quickly and heats up the surroundings.
- Energy is dissipated due to drag which causes particles in the surroundings to move more quickly.
- Efficiency = (useful energy transferred by the device)/(total energy supplied to the device)
Common misconception
Pupils may not realise that energy transfers usually result in the heating of the surroundings and therefore some energy ends up in a thermal store.
Pupils should have opportunity to identify and describe places in a system where energy is dissipated and transferred into a thermal store.
Keywords
Dissipate - Friction can cause energy to dissipate (spread out and become unusable) into the surroundings, causing them to heat up.
Efficiency - Efficiency is the fraction of energy supplied to an object or system that is usefully transferred by it.
Useful energy transferred - The amount of energy usefully transferred by an object or system is the useful energy transferred by the device.
Total energy supplied - The total amount of energy transferred to an object or system is the total energy supplied to the device.
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