Combustion is a word scientists use for burning. Combustion takes place when chemicals mix together and give off heat and light in the form of fire. For example, the charcoal in a barbecue grill burns because it mixes with oxygen in the air. The fire goes out if the grill is closed because air cannot reach the coals.

Some kinds of things can begin to burn without being started by a spark or flame. This is called spontaneous combustion. It can happen, for example, with a pile of oily rags. The chemicals inside the rags mix together and make heat. If the heat cannot escape, the rags get so hot that they finally start to burn.

mage to right: Combustion is burning. These materials contain chemicals that burn easily when heated. Credit: World Book illustration How to cite this article: To cite this article, World Book recommends the following format: "Combustion." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.