Examples of Energy Transfer

Mechanical Energy Transfers

Mechanical energy transfer happens when a force moves an object, causing energy to move from one place to another. This is called work done by the force. The energy transferred depends on the size of the force and the distance over which it acts.

For example, when you push a shopping trolley, your muscles do work on the trolley, transferring energy to it and causing it to move. Similarly, when an object falls, gravity does work on it, transferring energy as it moves downward.

The formula for work done is:

$$\text{Work done (J)} = \text{Force (N)} \times \text{Distance moved in the direction of the force (m)}$$

For instance, if you push a box with a force of 10 N over a distance of 3 m, the work done (energy transferred) is:

$$\text{Work done} = 10 \times 3 = 30 \text{ J}$$

Electrical Energy Transfers

Electrical energy transfer occurs when an electric current flows through a circuit. The electrical energy is transferred to other forms such as heat, light, or sound depending on the device.

For example, in a kettle, electrical energy is transferred to thermal energy to heat water. In a light bulb, electrical energy is transferred to light energy and some thermal energy.

The energy transferred electrically depends on the charge passing through the circuit and the potential difference, but power calculations are covered in other topics (see related notes on Power).

For instance, when a toaster is switched on, electrical energy flows through the heating element, transferring energy that heats the bread.

Heating Energy Transfers

Energy can be transferred by heating when a hotter object transfers energy to a cooler one. This happens through three main methods: conduction, convection, and radiation.

For example, when boiling water in a kettle, energy is transferred from the heating element to the water by conduction and convection. The water molecules gain energy, causing the temperature to rise.

Heaters transfer energy to the air by heating, warming up a room. The air near the heater gains energy and rises, allowing convection currents to spread warmth.

Energy transfer by heating always happens from a hotter object to a cooler one until thermal equilibrium is reached.

Radiation Energy Transfers

Energy can also be transferred by radiation, which involves waves carrying energy through space or air without needing a medium. This is how the Sun’s energy reaches Earth.

Light and infrared radiation are common examples of energy transfer by radiation. Infrared radiation transfers heat energy, which is why you feel warmth from a heater or the Sun even if you are not touching them.

Radiation can transfer energy through a vacuum, unlike conduction and convection which need particles.

For example, when you sit near a campfire, you feel warmth because infrared radiation transfers energy from the fire to your skin.