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

2. Topic 2 Potential and Kinetic Energy
Potential and kinetic energy in mechanical systems
Natural Sciences - Grade 7

3. Potential and kinetic energy in mechanical systems:
Mechanical systems need energy so that the system’s different parts can move.
Machines and tools can be used to do the work for us.
Potential energy can be changed to kinetic energy in a mechanical system.
All the different parts interact in a mechanism which is based on mechanical principles.
Natural Sciences - Grade 7

4. Natural Sciences - Grade 7
Mechanical systems
These are systems in which the input energy involves motors, machines, springs, stretched elastics, crane lifting a heavy generator, hitting a cricket ball with a cricket bat, bending a plastic ruler to shoot a small paper ball, a pulley lifting a tin of paint, scissors cutting paper, etc.
Natural Sciences - Grade 7

5. Natural Sciences - Grade 7
Mechanical systems
Energy in cyclist’s body [potential energy] → boy’s legs and feet move the pedals → pedals turn the cog and chain → chain turns the rear [back] cog → rear cog turns the wheels → bicycle moves forward [kinetic energy].
Natural Sciences - Grade 7

6. Thermal (heating) systems
These are systems in which heat is the input energy – for example heat from a candle, a burner or a stove. It could also be the transfer of heat from a hot cup of tea to the air as it cools.
Natural Sciences - Grade 7

7. Thermal (heating) systems
Stove plate [potential energy] → stove’s plate is switched on and heats up → heat of the stove’s plate heats the pot → heat of the pot heats the soup → soup gets hotter and starts to bubble and boil [kinetic energy
Natural Sciences - Grade 7

8. Thermal (heating) systems
A geyser stores heat energy in the hot water.
Natural Sciences - Grade 7

9. Natural Sciences - Grade 7
Electrical systems
Electrical systems use electrical energy to cause change or to do work.
These are systems in which electricity is the input energy such as a cell, battery or main electricity being used to operate an appliance.
Batteries store electrical energy in the chemicals that are inside the battery.
Natural Sciences - Grade 7

10. Natural Sciences - Grade 7
Electrical systems
Natural Sciences - Grade 7

11. Natural Sciences - Grade 7
Electrical systems
The electrical energy flows / moves through the electric circuits and it is then transferred to the output devices [bulbs; motors and buzzers].
A torch battery’s energy moves to the bulb to make the beam of light.
Natural Sciences - Grade 7

12. Natural Sciences - Grade 7
Sound energy
Anything that makes a noise because it is moving, is an example of mechanical energy.
Sound energy is the energy produced by sound vibrations as they travel through water, air or any other space.
The sound waves bounce / amplify as it moves.
The sound waves, like the ripples in a lake, become weaker the farther they travel.
The energy of the waves becomes more spread out.
Natural Sciences - Grade 7

13. Natural Sciences - Grade 7
Sound energy
Examples: car hooter, piano key, baby rattle, gun shot, etc.
Natural Sciences - Grade 7

14. Natural Sciences - Grade 7
Biological systems
Every living creature needs energy for their digestion and respiration.
The Sun supplies biological energy and it is stored in the form of chemical energy in plants and animals.
Natural Sciences - Grade 7

15. Natural Sciences - Grade 7
Biological systems
The process photosynthesis enables plants to convert the solar energy to chemical energy.
Natural Sciences - Grade 7

16. Natural Sciences - Grade 7
Biological systems
The input energy comes from a plant or animal which is eaten and it provides the biological energy to the animal or person who is eating.
The energy in the food that you eat is used to change your position when you run, walk, jog or move.
Energy is also used to make you think, breath and sustain all bodily processes.
Natural Sciences - Grade 7