Energy (Year 9)

Representing Energy

  • Energy is a property of a system — a system has a certain amount of energy.

  • The law of conservation of energy states that energy cannot be created or destroyed. That is, energy cannot appear out of nowhere and cannot disappear, instead it must go somewhere.

  • An open system transfers energy and mass between it and its surroundings. Therefore, the total energy content of an open system may change.

  • A closed system does not allow energy to be transferred to its surroundings. Hence, the total energy of a closed system remains constant.

  • Work is a process, an event that changes the energy of the system. The concept of work is necessary to add or remove energy from a system.

How to draw energy flow diagrams

  1. Identify your system (write it in a circle).

  2. Define the initial and final points in time.

  3. Energy stored in the system remains in the system (inside the circle).

  4. Identify what energy transformations are taking place in your system using arrows.

  5. Show work transferring energy into or out of the system as arrows crossing the circle.

Understanding Efficiency

Energy efficiency is the ratio of useful energy output to the total energy input. It is often described as a percentage and indicates how well energy is converted from on form to another. Higher efficiency means less energy waste. It is important in evaluating the performance of machines and systems.

Sankey diagrams

A Sankey diagram shows you how well a machine uses energy. In other words, it tells you if it uses it efficiently (without much waste) or inefficiently (with a lot of waste).

The thickness of the arrows shows how much energy is involved. The length of the arrows does not matter in a sankey diagram. Useful energy transfers are shown from left to right. Wasteful energy transfers are shown going downwards.

Summarising Case Studies

Issue

Identify the key energy use issues from the case study, such as the amount of energy consumed and the activities or processes that contribute most to the total.

Action

Outline the change(s) that were made to improve energy efficiency and identify any resources that were required to make the change.


Impact

Explain the improvements that were observed and how they improved the business.