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Unit 3: The Solar System and energy

Where Does Energy Go — HIA International - Grade 6 Revision Notes & Topical Questions

5 min read 8 parts Lesson 14 of 14 2 quizzes

📚 HIA International - Grade 6 Hub / Topical Revision
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Lesson summary

3.7 Where does energy go?

  • 3.7 Where does energy go? — HIA INTERNATIONAL notes
  • Every energy change
  • Useful energy
  • Wasted energy
  • Dissipated energy
  • Cannot be recovered

Part 1 of 6Useful and wasted energy

Every energy change
  • Every energy change some of the energy changed or transferred is useful and some is wasted
Useful energy
  • Useful energy the energy changed into the form that is wanted
Wasted energy
  • Wasted energy energy that is changed into forms that are not wanted, usually thermal energy and sound

Part 2 of 6Energy in a motorcycle

1Useful
  • Useful chemical energy in the fuel is changed to kinetic energy to move the motorcycle and rider
2Wasted
  • Wasted chemical energy is also changed into thermal energy and sound energy
3Amount
  • Amount only about 25% (one quarter) of the chemical energy in the fuel is used for movement, and about 75% is wasted

Part 3 of 6Dissipated energy

Dissipated energy
  • Dissipated energy energy that spreads out where there is no use for it
Cannot be recovered
  • Cannot be recovered thermal energy and sound cannot be gathered back into one place to be stored, changed or transferred
Always happens
  • Always happens for everything that uses an energy change or transfer, some of that energy will always be dissipated

Part 4 of 6Comparing two lamps

LampElectrical energy changed to lightElectrical energy wasted as thermal energy
Lamp Aabout 15%about 85%
Lamp Babout 50%about 50%

Part 5 of 6Wasted thermal energy when heating

1Heating water over a fire
  • Heating water over a fire chemical energy in wood is changed to thermal energy by burning
2Useful
  • Useful thermal energy heats the water
3Wasted
  • Wasted thermal energy also heats the rocks, the metal container and the air, and escapes in the steam
4Light
  • Light the fire also changes some energy into light, which is not the energy wanted

Part 6 of 6Dissipation of energy

Dissipation of energy
Hot objects cooling
  • Hot objects cooling the temperature of a hot object falls with time as its thermal energy spreads out to the surroundings
Moving away from a hot object
  • Moving away from a hot object you feel less heat the further you are from it, because the temperature falls with distance
Waves
  • Waves the energy in a wave dissipates as the wave travels

Key terms

TermMeaning
Useful energyEnergy changed into the form that is wanted.
Wasted energyEnergy changed into forms that are not wanted.
DissipatedSpread out where there is no use for it.
RecoveredGathered back so that it can be used again.
Thermal energyHeat energy, which is usually the wasted form.

Avoid these mistakes

1
Saying wasted energy disappears — it is dissipated into the surroundings
2
Saying dissipated energy can be collected and used again — it cannot be recovered
3
Saying a device changes all of its energy into the useful form — some is always wasted
4
Mixing up the two lamps — Lamp B wastes less energy because it changes a greater share into light

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