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A computer model is a representation of a real-life system or situation, such as the workings of a nuclear reactor or the evacuation of a football stadium.

A collection of rules is created to study what would happen in real-life situations. Changes are made to see how they affect the outcome. For example, before a new football stadium is built, a computer model could be used to see if there are enough fire exits and if they’re in the safest places.

Simple models can be built in a spreadsheet. A spreadsheet model could be used to plan a school prom. To make sure it came in on budget the spending on food, drinks, entertainment, and the price of tickets could be varied.

It could also be used to see how much money would be made from ticket sales. These are called 'what if…' questions, for example:

• What if only 20 people attend?
• What if costs go up by 10 per cent?

More complicated models can be built to replicate real-world phenomena such as water, fire and weather. Watch the clip below to see how computers can be used to model special effects in films.