成人快手

Key points

  • When is stored within a , equations can be used to quantify how much is stored.

  • Energy is conserved. It cannot be created or destroyed. Energy can be transferred between stores.

  • The total energy has the same value before and after any changes.

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The gravitational potential energy store

As an object is lifted, is done against the force of gravity.

The higher the object, the more energy is in the gravitational potential energy store.

The diagram shows a rocket at different heights. The gravitational potential energy of the rocket increases from zero as it lifts off the ground and goes higher.
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Energy in the gravitational potential energy store ( Ep)

Use the following equation to calculate how much energy is stored in the :

Energy in the gravitational potential energy store (Ep) = mass (m) x gravitational field strength (g) x height (h)

\(Ep = m \times g \times h\)

The unit of measurement for energy in the gravitational potential energy store is the joule (J).

On Earth, the (g) is 9.8 N/kg.

A female diver prepares to dive off a diving board.

Example

A diving platform is 10 m above the ground. When an 80 kg diver climbs to the top of the platform, how much is the increase in energy in their gravitational potential energy store?

A female diver prepares to dive off a diving board.

Energy in the gravitational potential energy store = ?

Mass = 80 kg

Gravitational field strength = 9.8 N/kg

Height = 10 m

use the following equation:

Energy in the gravitational potential energy store (Ep) = mass (m) x gravitational field strength (g) x height (h)

\(Ep = m \times g \times h\)

\(Ep = 80 \times 9.8 \times 10\)

\(Ep = 7~840~J\)

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The kinetic energy store

The faster an object is travelling, the more energy there is in the kinetic energy store of the object.

How fast the object is moving is its speed. Speed is measured in m/s.

Velocity is speed in a particular direction. Velocity (v) is also measured in m/s.

The diagram shows three identical cars at different velocity. The kinetic energy store of an object increases as its velocity increases.

The more mass an object has, the more energy in the kinetic energy store.

The diagram shows three identical vehicles with different masses. The kinetic energy store of an object increases as its mass increases.
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Energy in the kinetic energy store (Ek)

Use the following equation to calculate the amount of energy in the of a moving object:

Energy in the kinetic energy store (Ek) = 0.5 x mass (m) x velocity虏 (v虏)

\(Ek = 0.5 \times m \times v虏\)

The unit of measurement for the amount of energy in the kinetic energy store is the joule (J).

Example

A runner with a mass of 60kg is running at a speed of 1 m/s. Calculate the amount of energy in their kinetic energy store.

Energy in kinetic energy store = ?

Mass = 60 kg

Velocity = 1 m/s

Use the following equation:

Energy in the kinetic energy store (Ek) = 0.5 x mass (m) x velocity虏 (v虏)

\(Ek = 0.5 \times m \times v虏\)

\(Ek = 0.5 \times 60 \times 1虏\)

\(Ek = 0.5 \times 60 \times 1\)

\(Ek = 30~J\)

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Test your knowledge

Quiz - Multiple choice

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Play the Atomic Labs game! game

Try out practical experiments in this KS3 science game.

Play the Atomic Labs game!
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