Energy Transfer Examples

This lesson covers:

  1. How energy is transferred (mechanically, electrically, by heating, by radiation)
  2. Examples of energy transfers

Conservation of energy law


Energy cannot be created or destroyed. It can only be transferred from one form to another.

Example 1: A coal fire


Scenario:

A fire burns fuel such as coal to produce heat.

Illustration of a coal fire showing energy transfer from chemical energy to thermal energy.

Energy transfer:

  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.

Example 2: Car braking


Scenario:

A driver slows a car from 15 m/s to rest.

Illustration of a car braking to demonstrate energy transfer.

Energy transfer:

  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.


Example 3: Archer firing a bow and arrow


Scenario:

An archer pulls the string of the bow back and loads an arrow. The archer then releases the string allowing the arrow to fire.

Illustration of an archer firing a bow and arrow

Energy transfer:

  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 mechanically to the kinetic energy store of the arrow.


What type of energy is stored in the string of a bow when it is pulled back?

Elastic potential energy

Kinetic energy

Thermal energy

Chemical energy

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Which energy store increases when an object is lifted 1.5 m above the ground?

Nuclear

Gravitational potential

Chemical

Thermal

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A ball lifted 1.5 m above the ground has 20 J of gravitational potential energy. The ball is dropped.


What is the kinetic energy of the ball just before it hits the ground? Ignore air resistance.

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20 J

20 W

0 J

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Which of the following shows the useful energy transfer that takes place when a battery powered toy car travels across the floor?

kinetic → gravitational potential

chemical → thermal

thermal → kinetic

chemical → kinetic

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A toy car has a spring which stores elastic potential energy. When released, the toy car moves across the floor. 


Which of the following is the energy transfer mechanism for the toy car?

mechanically

radiation

heating

electrically

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