Level: JHS, Basic 8 | Subject: Integrated Science | Strand: Forces and Energy | Topic: Conservation of Energy
Curriculum reference: NaCCA Basic 8 Integrated Science, Forces and Energy. These notes cover the standard scope of the topic and are checked against the GES General Science learner materials.
1. The Law of Conservation of Energy
Energy cannot be created or destroyed. It can only change from one form to another. The total energy before a change is equal to the total energy after the change.
- Energy is the ability to do work. Its unit is the joule (J).
- When we say energy is “used up”, it has really changed into other forms, often heat that spreads into the air and cannot be collected again.
2. Forms of Energy
| Form | Example |
|---|---|
| Kinetic | A moving car, a running player |
| Potential | Water behind a dam, a stretched rubber band, a coconut on a tree |
| Heat | A burning charcoal stove |
| Light | The Sun, a bulb |
| Sound | A drum, a radio |
| Electrical | Current in a wire |
| Chemical | Food, fuel, dry cells |
| Nuclear | The Sun and nuclear power stations |
3. Energy Transformations
| Device or event | Energy change |
|---|---|
| Electric bulb | Electrical to light and heat |
| Electric fan | Electrical to kinetic |
| Radio | Electrical to sound |
| Solar panel | Light to electrical |
| Charcoal stove | Chemical to heat and light |
| Dry cell torch | Chemical to electrical to light |
| Plant making food | Light to chemical |
| Hydroelectric dam (Akosombo, Bui) | Potential to kinetic to electrical |
An energy chain shows the steps. Example: Sun (light) to plant (chemical) to maize (chemical) to a girl eating banku (chemical) to her running (kinetic and heat).
4. Conservation in a Falling or Swinging Object
When an object falls, it loses potential energy and gains the same amount of kinetic energy (if we ignore air resistance).
- At the top: all potential energy, no kinetic energy.
- Half way down: half potential, half kinetic.
- Just before the ground: all kinetic energy, almost no potential energy.
A swinging pendulum does the same. At the highest point it has maximum potential energy. At the lowest point it has maximum kinetic energy. Over time it stops because some energy changes to heat through air resistance and friction.
Worked example. A 2 kg mango falls from a branch 5 m high. Take g = 10 N/kg. PE at the top = m x g x h = 2 x 10 x 5 = 100 J. Just before it lands, KE = 100 J.
5. Efficiency and Wasted Energy
No machine changes all its input energy into useful output. Some is always wasted as heat or sound.
Efficiency = (useful energy output / total energy input) x 100%
Example: a bulb takes in 100 J and gives 20 J as light. Efficiency = 20 / 100 x 100 = 20%. The other 80 J is heat. The total is still 100 J, so energy is conserved.
6. Sources of Energy
- Renewable: solar, wind, hydro (water), biomass, geothermal. They are replaced naturally.
- Non-renewable: coal, crude oil, natural gas. They took millions of years to form and will run out.
Solar panels (photovoltaic cells) change sunlight directly into electricity. Ghana has plenty of sunshine, so solar energy can reduce our use of fossil fuels. Benefits are cleaner air, lower carbon emissions and energy we can produce at home. Challenges are the high starting cost, no power at night or on cloudy days, and the need to store energy. The Bui Power Authority solar project in the Bono Region is one example of large solar generation in Ghana.
7. Saving Energy at Home and School
- Switch off lights, fans and TVs when not in use.
- Use energy-saving (LED) bulbs.
- Use daylight and open windows instead of lights and fans where possible.
- Cook with lids on pots and use efficient stoves.
- Use solar power where you can.
Remember: Energy is never lost. It only changes form. Useful energy goes down because more of it turns into wasted heat.
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Education Always (education.inspiringalways.com). Original notes written to follow the NaCCA Basic 8 Integrated Science curriculum.