# 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

• 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

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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