Energy Transfers in a System

Conservation of Energy

Let’s remind ourselves of the conservation law of energy.

“Energy cannot be created or destroyed, only transferred from one store to another”

Useful and Wasted Energy

In a system, when energy is transferred- some of it is useful energy and some is wasted energy.

Useful energy is energy which is required for the object to work. For example, when a car moves the useful energy is kinetic energy.

Wasted energy is energy that is transferred to a store which is not useful. For example, when a car moves it also transfers energy into the thermal store as it gets hot. The thermal energy is a wasted energy, the car getting hot does not help it to move.

The most common wasted energy in any system is thermal energy, but there can be other wasted energy stores depending on the scenario.

Reducing Wasted Energy

There are a number of different ways in which we can reduce the amount of energy that is wasted and make the process more energy efficient.

1. One way is to improve lubrication between moving parts and reduce the amount of friction. With reduced friction, less energy is wasted in the thermal store.
2. Another way is thermal insulation. This can help to keep the heat inside an object, where it is supposed to be kept e.g. a thermos flask. Since energy is being kept where it is supposed to be, less energy is required to continually reheat the system.

Thermal Conductivity

Thermal conductivity is a measure of how well energy is transferred across a material. The higher the thermal conductivity the higher the rate of energy transfer.

Application of Thermal Conductivity

In general, the thicker the material the lower the rate of energy transfer. This means that a person can easily increase or decrease the rate of energy transfer by either decreasing or increasing the thickness accordingly.

For example, a house with thick walls will keep its heat for longer than a house with thin walls.

What is useful energy?

Your answer should include: Desired / Required
Explanation: Energy that is desired or required

How can one reduce the amount of energy wasted?

Your answer should include: Lubrication / Insulation

The lower the thermal conductivity the __________ energy transfer.

Lower