Energy transfer examples

• How can energy be transferred?

  Mechanically e.g. when gravity accelerates an object and gives it kinetic energy.

  Electrically e.g. when a current passes through a lamp and it emits light and heat.

  By heating e.g. when a fire is used to heat up an object.

  By radiation e.g. when vibrations cause waves to travel through the air as sound, or an object emits electromagnetic radiation.
• What is the conservation of energy law?Energy cannot be created or destroyed. It can only be transferred from one form to another.
• How is energy transferred when a fire burns fuel such as coal to produce heat?

  1. Coal has a large store of chemical energy (energy within chemical bonds).
  2. When coal is burned the chemical energy is transferred by heating to the thermal energy store of the coal.
  3. Hot coals and flames transfer energy to the surroundings by heating and radiation.
• How is energy transferred when a driver slows a car from 15 m/s to rest?

  1. The moving car has kinetic energy.
  2. The brakes mechanically do work on the car to slow it down.
  3. The kinetic energy of the car decreases and the thermal energy store of the brakes increases.
• How is energy transferred when an archer pulls the string of the bow back and loads an arrow. The archer then releases the string allowing the arrow to fire?

  1. As the string of the bow is pulled back chemical energy in the archers muscles is transferred mechanically to the elastic potential of the bow.
  2. When the archer releases the string of the bow, the elastic potential energy of the string is transferred mechanicallyto the kinetic energy store of the arrow