Topic 5 of 8 · Grade 7
Energy and simple machines
Heat, light, sound, movement (kinetic), electrical, chemical (stored in food and fuels) and stored (potential) energy. Energy changes from one form to another: a torch changes chemical energy into light.
Notes for this topic 1 file, in order
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Forms of energy
Heat, light, sound, movement (kinetic), electrical, chemical (stored in food and fuels) and stored (potential) energy. Energy changes from one form to another: a torch changes chemical energy into light.
Sources of energy
- Non-renewable: coal, petrol, diesel, gas (they will run out).
- Renewable: sun (solar), wind, water (hydro – Kariba), biogas, wood (if trees are replanted).
Saving energy
Switch off lights, use energy-saving bulbs and solar power, use fuel-efficient stoves.
Forces
Pushes and pulls; friction slows things down; gravity pulls things towards the Earth.
Simple machines
Machines make work easier.
- Lever: a rigid bar turning on a pivot (fulcrum) – crowbar, wheelbarrow, scissors, bottle opener.
- Pulley: a wheel with a rope – lifting a bucket from a well.
- Wheel and axle: bicycle, scotch cart.
- Inclined plane (ramp), wedge (axe), screw.
Worked example: Why does a long-handled crowbar make it easier to lift a heavy stone?
The longer the handle (distance from the pivot), the less effort is needed.
Check yourself
- Give two renewable sources of energy.
- What energy change happens in a radio?
- Name a simple machine used to lift water from a well.
Show answers
- Any two: solar, wind, hydroelectric, biogas.
- Electrical energy to sound energy.
- A pulley (or windlass/wheel and axle).
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