Level: JHS, Basic 7 | Subject: Integrated Science | Strand: Forces and Energy | Topic: Forms of Energy
Curriculum reference: B7.4.1.1.1 and B7.4.1.1.2 (NaCCA Integrated Science). The indicators are merged into one set of notes.
1. What is Energy?
- Energy is the ability to do work. Anything that moves, grows, glows or gets hot is using energy.
- The unit of energy is the joule (J).
- Energy cannot be seen, but we see what it does.
2. Forms of Energy
| Form | Meaning | Everyday example |
|---|---|---|
| Potential energy (PE) | Energy stored in an object because of its position or condition | A mango on a tree, water behind the Akosombo Dam, a stretched catapult |
| Kinetic energy (KE) | Energy of a moving object | A running footballer, a moving trotro, flowing water |
| Heat (thermal) energy | Energy from hot objects | A charcoal fire, the sun |
| Light energy | Energy we see | Sunlight, a torch, a bulb |
| Sound energy | Energy from vibrating objects | A drum, a radio, a bell |
| Electrical energy | Energy from moving charges (electric current) | Electricity from ECG, a dry cell |
| Chemical energy | Energy stored in food, fuel and batteries | Fufu and soup, petrol, firewood, a dry cell |
| Solar energy | Energy from the Sun | Solar lamps, solar panels, drying cocoa and fish |
| Nuclear energy | Energy stored in the nucleus of atoms | A nuclear power station |
3. Potential and Kinetic Energy
- Gravitational potential energy: PE = m × g × h, where m is mass in kg, g is 10 m/s² (gravity) and h is height in metres.
- Kinetic energy: KE = ½ × m × v², where v is speed in m/s.
- PE increases with mass and height. KE increases with mass and speed.
- Mechanical energy = PE + KE. When a ball falls, PE changes to KE.
Worked examples
1. A 2 kg stone is on a roof 5 m high. PE = 2 × 10 × 5 = 100 J.
2. A 4 kg ball moves at 3 m/s. KE = ½ × 4 × 3 × 3 = 18 J.
4. Everyday Uses of Energy
| Gadget or activity | Energy form used |
|---|---|
| Electric iron, kettle, cooker | Electrical to heat |
| Bulb, torch | Electrical (or chemical) to light |
| Radio, loudspeaker | Electrical to sound |
| Solar lantern | Solar to electrical to light |
| Eating food | Chemical energy for the body |
| Vehicle engine | Chemical (fuel) to kinetic |
Remember: PE is stored energy and KE is moving energy. PE = mgh and KE = ½mv². Mechanical energy is PE plus KE.
Ready to practise?
Education Always (education.inspiringalways.com). Original notes written to follow the NaCCA Basic 7 Integrated Science curriculum.