Energy transfers — Science, 11–13 years
Energy does not simply disappear when something stops moving or gets colder. It is transferred between stores, often spreading into the surroundings as thermal energy. Tracking these changes helps explain machines, food, batteries and exercise.
Idea
Energy is what can make things happen: an object can move, heat up, light up or change shape. It can be stored in moving objects, stretched springs, fuels, batteries and raised objects. During an event, energy is transferred from one store to another; some usually spreads to the surroundings as heating.
Why track energy?
People once described a machine only by saying what went in and what came out. That made it hard to compare machines or explain why some waste more energy. Energy accounting solves this problem: it asks where energy starts, which transfers are useful, and where energy spreads. It shows that wasted energy is not destroyed, just harder to use.
Worked example
A 100-joule battery powers a lamp. Step 1: 35 joules become useful light. Step 2: subtract: 100 − 35 = 65 joules. Step 3: the 65 joules are transferred mainly as heating in the lamp and room. The total is still 100 joules; the energy has changed form and spread out.
A common trap
A common thought is that energy is used up when a battery goes flat. That makes sense because the device stops working and the battery feels empty. In science, the stored chemical energy has been transferred, mostly into heating and other forms that are spread through the surroundings. It has not vanished.
Outside school
Energy transfers help engineers design efficient appliances, bicycles and vehicles. A kettle transfers electrical energy to heating, while insulation slows the transfer from hot water to the room. Athletes also rely on transfers: chemical energy from food becomes movement and heat in muscles.
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