Section 1: Definition of Energy:

  • Energy is the capacity  to provoque changes.
  • Different changes are associated with different types of energy.


  • When we ride our bike we cause changes of motion. This is mechanical energy.
  • When we boil water we cause changes of temperature and of state. This is thermal energy.
  • When we use our mobile phone, its batteries get discharged. This is electrical energy.

Energy can not be created out of nothing. It can not disappear either. The only thing we can do with energy is to transform it from one typo to another. This is an important fact known as the Energy conservation law.

An useful way to think about the energy conservation law is the cycle of energy:


Thermal energy can be transformed into mechanical, like in car engines.

Mechanical energy can be transformed into electrical energy, like in wind generators.

Electrical energy can be transformed into thermal energy, like in electric heaters.

The opposite transformations are also possible, so the cycle works either clockwise or counterclockwise.



Printable summary of Section 1

Section 2: Sources of energy

Non renewable sources of energy: fossil fuels and uranium:

  • Coal
  • Petrol
  • Gas
  • Nuclear

Renewable sources of energy: they come ultimately from the sun:

  • Solar
  • Wind
  • Hydraulic

Energy sources summary

Section 3: Power plants

How do we get electrical energy from these sources?

Section 4: Heat engines:

Summary U7 (Energy)





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