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Chapter 18
Chapter 19
Chapter 20
Chapter 21
Chapter 22
Chapter 23
Chapter 24
Chapter 25
Chapter 26
Chapter 27
Chapter 28
Chapter 29
Chapter 30
Chapter 31
Chapter 32
Chapter 26 Energy transfers
 
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1.

Types of energy

  • There are eight different types of energy:
    – electrical energy
    – kinetic energy
    – heat (thermal energy)
    – potential energy
    – light
    – elastic energy
    – sound
    – chemical energy
  • Energy is continually being changed from one type to another. For example, when floodlights illuminate a pitch, electrical energy is changed into light and heat. When someone plays a guitar, chemical energy in their body is changed first into elastic energy in the guitar strings, and then into sound.
2.

Energy transfers
Heat (thermal energy) can be transferred from one place to another by three different processes – conduction, convection and radiation.

  • Conduction – when hotter, vibrating particles pass on their kinetic energy to cooler neighbouring particles without the material(s) moving.


  • Convection – when heated liquid or gas becomes less dense than colder surrounding material. The hotter, less dense material rises and the colder, more dense material sinks, causing convection currents. For example, convection currents of air carry hand gliders higher.


  • Radiation – when invisible, infra-red electromagnetic waves are given off from hot objects. The waves can pass through air or through a vacuum.
    For example, the Earth is heated by radiation from the Sun.
3.

Emitting (giving out) and absorbing (taking in) radiation

  • Dark, dull surfaces are good emitters and good absorbers of radiation.
  • Light, shiny surfaces are poor emitters and poor absorbers of radiation.
  • Shiny surfaces are good reflectors of radiation.
4.

Reducing energy loss from our homes
It is important to reduce the loss of heat from our homes. This is done by increasing the insulation of our homes using the methods shown in the diagram below.

5.

Conservation of energy

  • Energy can be changed from one form to another and transferred from one machine to another, but it cannot be created or destroyed. This law is called
    the Law of Conservation of Energy.
  • Machines (e.g. motor cars, kettles) are often used to convert energy from one form to another. But these and all other energy transfers are never perfect. Some energy is always lost (very often as heat) during the transfer.
  • The efficiency of a
   
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