1. Natural Sciences Grade 7
Term 3: Energy and Change
Potential and kinetic energy

2. Topic 2 Potential and Kinetic Energy
Law of conservation of energy
Natural Sciences - Grade 7

3. Law of conservation of energy
Energy cannot be created or destroyed, but it is changed or converted from one form to another.
Energy flows / transfers between different parts of a system.
We can study this transfer of energy within a system through flow diagrams.
Natural Sciences - Grade 7

4. Flow diagram example: Plastic Ruler
NB: When drawing an energy flow diagram you need to identify:
Where the energy comes from (the input energy).
Where the energy goes ( transfer into output energy).
The changes in potential and kinetic energy in the process.
The bent ruler has elastic potential energy.
The potential energy changes to kinetic energy when the bent ruler is released.
The ruler bends.
Natural Sciences - Grade 7

5. Flow diagram example: Water wheel Wind up toy car [above]
Gravity lets the water fall onto the fins of the water wheel. Gravitational potential Energy is changed to kinetic energy.
The falling water causes the water wheel to turn.
The water at a height, has gravitational potential energy.
A person has to wind up the toy car. It now has elastic potential energy.
The elastic potential energy is now changed to kinetic energy.
The toy car moves.
Natural Sciences - Grade 7

6. Flow diagram example: Electrical toy car [example]
Cells have potential energy.
Circuit is closed and an electric current starts to flow.
The electric current flows and turns the motor.
The electric motor turns the wheels and the car moves [kinetic energy]
Natural Sciences - Grade 7

7. Flow diagram of the energy system
Flow diagram of the energy system of a boy eating a banana.
Banana
[potential energy].
Boy eats the banana.
Energy is stored in the boy’s muscles.
The boy runs
[kinetic energy].
Natural Sciences - Grade 7