A set of rules, relationships and processes needs to be defined. Some simulations will involve complex mathematical formulae.

Simple simulations may be done on spreadsheets but complex programs would be needed to simulate many situations.

Examples:

Aircraft flight simulator - models the behaviour of an aircraft under specific conditions of windspeed, altitude etc and the way it is handled by the pilot.
	A simulation of an insect population may include variables such as food supply, climate and predators. Changing one of these variables would show how the population would be affected.
Games - Some games simulate a human community including variables such as wealth, availability of water, overcrowding, food, entertainment etc..

Advantages of simulations

• any risk of danger to humans is eliminated (eg radio-active, fire-fighting, spaceflight, aircraft flight)
• can be done in comfort (eg weather, heat and cold)
• can investigate 'improbable' conditions which are almost unattainable in reality.

Disadvantages of simulations

• reality is complex and only an approximation of reality can be achieved.
• complex programming involved
• may be expensive hardware needed (eg flight control simulators)