Physics
Potential energy Learning objectives: • consider what happens when a spring is stretched • describe what is meant by gravitational potential energy • calculate the energy stored by an object raised above ground level.
Key words energy transfer elastic potential energy gravitational potential energy gravitational field strength
On Jupiter, gravity is three times stronger than on Earth. If the same mass was lifted to the same height on Earth and Jupiter, on Jupiter it would store three times the gravitational potential energy.
Stored energy When a spring is stretched it stores energy. We call this potential energy. The stretched spring stores elastic potential energy. It stretches more if a greater force is applied, and returns to its original length when the force is removed. Compressed springs are also used to store elastic potential energy, for example, to keep the batteries in position in a mobile phone. 1
Imagine slowly stretching a rubber band. Describe what you would feel as you stretch it more.
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Suggest what happens to the amount of energy stored in the spring inside a the toy in Figure 1.2 as the key is turned.
Water stored behind a dam also stores potential energy. It is called gravitational potential energy (GPE). The GPE stored by an object can be increased by moving it upwards. For example, you gain GPE by going up stairs. 3
An aircraft is flying horizontally at a height of 10 000 m. Explain whether its gravitational potential energy is increasing, decreasing or remaining constant.
Figure 1.1 A stretched catapult stores elastic potential energy
Figure 1.2 Turning the key twists a spring inside the toy. This stores elastic potential energy which can be transferred to kinetic energy
Calculating changes in gravitational potential energy Tom lifts a box. The amount of gravitational potential energy gained by the box depends on: • the mass of the box, m, in kilograms, kg • the height Tom raises the box, h, in metres, m. We can calculate the amount of gravitational potential energy gained (Ep) using the equation: Ep = mgh
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Figure 1.3 The stored gravitational potential energy of water held behind a dam can be transferred to kinetic energy if the water is released
AQA GCSE Physics: Student Book
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