Unit 10: Energy Transformations
Energy is never created or destroyed — it is only transformed from one store into another, or transferred from one place to another. This unit explores how and why energy changes form.
01 Energy stores
Physicists describe energy as being held in different "stores." Common ones include: kinetic (movement), gravitational potential (height), elastic potential (stretched/squashed objects), chemical (food, fuel), thermal (temperature), and electrical.
02 Conservation of energy
The Law of Conservation of Energy: energy cannot be created or destroyed — it can only be transformed from one store to another, or transferred from one object to another. The total amount of energy always stays the same.
Example: a falling ball transforms gravitational potential energy into kinetic energy as it falls.
03 Efficiency and wasted energy
In every real transformation, some energy is "wasted" — usually transferred to the surroundings as heat, due to friction or resistance. This wasted energy is not destroyed; it simply spreads out and becomes harder to use.
efficiency = (useful energy output ÷ total energy input) × 100%
V Key vocabulary
| Term | Meaning |
|---|---|
| Energy transformation | A change from one type of energy store to another. |
| Conservation of energy | The principle that total energy remains constant; it is only transformed or transferred. |
| Efficiency | The percentage of input energy usefully transformed. |
| Dissipated energy | Energy that spreads out into the surroundings, usually as heat, and becomes less useful. |
? Quick check
Try to answer before you tap. Answers are hidden underneath.
A lamp receives 100 J of electrical energy and produces 20 J of light energy. Calculate its efficiency.
20% (efficiency = 20 J ÷ 100 J × 100% = 20%). The other 80 J is mostly wasted as heat.
Describe the energy transformation as a skier slides down a snowy slope.
Gravitational potential energy is transformed into kinetic energy, with some energy dissipated as heat and sound due to friction with the snow and air resistance.
Why can no machine ever be 100% efficient in real life?
Because some energy is always dissipated to the surroundings, usually as heat, due to friction, air resistance, or electrical resistance.