AQA GCSE Physics

Revision Notes

1.1.11 Conservation & Dissipation of Energy

Conservation of Energy

  • The law of conservation of energy states that:

Energy cannot be created or destroyed, it can only be moved from one store to another

  • This means the total amount of energy in a closed system remains constant but can change where, and how, it is stored
  • Energy can therefore not necessarily be ‘lost’, but just transferred into wasted energy (often heat)

Examples of Energy Conservation

  • Conservation of energy applies to all energy changes

Example 1: A Television

  • The energy changes in televisions are:

electrical energy ➝ light energy + sound energy + thermal energy

  • Light and sound energy are useful energy transfers whereas thermal energy (from the heating up of wires) is wasted

Useful and wasted energy conversions for a television

Example 2: Heaters

  • The energy changes in an electrical heater:

    electrical energy ➝ thermal energy + sound energy + light energy

  • In a gas cooker, the energy transfers are similar but the initial source of energy is different:

chemical energy ➝ thermal energy + sound energy + light energy

  • In both these cases, thermal energy is useful, whereas sound and light are not

Useful and wasted energy conversions in an electric heater and gas cooker

Example 3: Rollercoasters

  • A rollercoaster increases its speed as it travels down a steep section of track and gains kinetic energy (KE)
  • When the rollercoaster travels up a steep section of track, this kinetic energy is transferred into gravitational potential energy (GPE)
  • These energy changes happen several times during a rollercoaster ride as the track goes up and down and around

WE - Energy transfers question image, downloadable AS & A Level Physics revision notes

  • As the rollercoaster in the diagram travels from A to D, the energy changes that take place are:

GPE ➝ KE ➝ GPE ➝ KE

  • Some energy is transferred to the surroundings as heat and sound energy too
  • At point A:
    • The rollercoaster is raised above the ground, therefore it has GPE
    • As it travels down the track, GPE is converted to KE and the roller coaster speeds up
  • At point B:
    • KE is converted to GPE as the rollercoaster rises up the loop
  • At point C:
    • This GPE is converted back into KE as the rollercoaster travels back down the loop
  • At point D:
    • The flat track means the rollercoaster only has KE

Example 4: Trampoline

  • When jumping on a trampoline the energy changes are:

elastic potential energy ➝ kinetic energy ➝ gravitational potential energy

  • Some energy is transferred to the surroundings as heat and sound energy too

Conservation of Energy Trampoline, downloadable AS & A Level Physics revision notes

Energy conversions for someone jumping on a trampoline

Worked Example

Describe the energy transfers in the following scenarios:

a) A falling object

b) A battery powering a torch

c) A mass on a spring

Part (a)

    • For a falling object:

gravitational potential energy ➝ kinetic energy

Part (b)

    • For a battery powering a torch:

chemical energy ➝ electrical energy ➝ light energy

Part (c)

    • For a mass on a spring:

elastic potential energy ➝ kinetic energy

Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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