🔋 Sources and Forms of Energy
1. Energy is the ability or capacity to do work.
2. Energy cannot be destroyed, but it can be converted from one form to another.
3. Energy is measured in Joules (J).
1. There are two main categories of energy:
- (a) potential energy — stored energy: chemical potential energy, gravitational potential energy and elastic potential energy, and
- (b) kinetic energy — the energy of motion.
2. Other common forms of energy include:
- heat, sound, light and electrical energy.
1. Kinetic energy is the energy that a moving object has due to its motion.
2. The amount of kinetic energy depends on speed and mass:
- (a) faster speed → more kinetic energy,
- (b) greater mass → more kinetic energy, and
- (c) a stationary object has no kinetic energy.
A ball at rest has no kinetic energy. The same ball moving faster has more kinetic energy, and a heavier ball at the same speed also has more kinetic energy.
1. Chemical potential energy is stored energy found in food, fuels and batteries.
2. It is released by chemical reactions.
- Food — chemical potential energy that living things use for life processes.
- Fuels (e.g., coal) — released as heat energy when burned.
- Batteries — released as electrical energy.
1. Gravitational potential energy is stored energy due to position above the ground.
2. It depends on the mass and height of the object:
- (a) greater height → more gravitational potential energy, and
- (b) greater mass → more gravitational potential energy.
3. Example: a ball held higher, or a heavier ball at the same height, stores more energy.
1. Elastic potential energy is stored energy in stretched or compressed objects, such as rubber bands and springs.
2. It depends on:
- (a) the extent of stretching / compression — more stretch → more energy,
- (b) the force applied — stronger force → more energy,
- (c) the thickness of the elastic object — thicker → more energy, and
- (d) the number of elastic objects used.
1. Energy cannot be created or destroyed.
2. It can only be stored, transferred or converted into other forms.
Brick dropped from a height — potential energy decreases and kinetic energy increases as it falls. At ground level, most of the potential energy has been converted to kinetic energy.
Bouncing ball — loses energy on each bounce because some kinetic energy is converted to heat and sound energy, so it bounces lower each time (less kinetic energy available).
Slingshot with rubber band — more stretch → more elastic potential energy → converted to more kinetic energy.
Ball collision — the kinetic energy of one ball is transferred to another when they collide.
1. Energy sources can be grouped into renewable and non-renewable sources.
Sun (solar) — clean, renewable. But solar panels do not work at night and are expensive.
Water (hydroelectric) — renewable, does not pollute. But dams harm aquatic wildlife and are expensive.
Wind — renewable. But only works when wind is available.
Fossil fuels — cheap, easy to use and transport. But non-renewable, release greenhouse gases and cause pollution.
1. Hydroelectric power station:
- Water stored → gravitational potential energy.
- Flowing water → kinetic energy.
- Spinning turbine → kinetic energy.
- Generator → electrical energy.
2. Fossil fuel power station:
- Coal (chemical potential energy) → heat energy (burning).
- Heat produces steam → kinetic energy (rising steam).
- Turbine spins → kinetic energy.
- Generator produces → electrical energy.
1. Ways to conserve energy:
- (a) use electrical appliances with lower power ratings,
- (b) switch off lights when not in use,
- (c) avoid opening refrigerator doors unnecessarily,
- (d) wash clothes by hand if only a few items, and air-dry instead of tumble drying, and
- (e) walk, cycle or use public transport instead of driving.