What fire needs — Chemistry, 7–10 years
Fire is a fast chemical change that needs fuel, oxygen and enough heat. Remove any one of these and the flame goes out, which is why this is useful for both lighting and safety.
The fire triangle
A flame keeps going only when three things meet: something to burn, oxygen from the air and enough heat. These are called fuel, oxygen and heat. Fire is the visible sign of a fast change that gives out heat and often light.
Why does a candle go out?
People needed a way to explain why a fire stops, not just why it starts. Covering a flame showed that it uses something in the air. The three-part rule grew from tests like this and also explains why fire blankets and lids can be useful.
Putting out a candle
Light a candle and place a glass over it without touching the flame. At first it burns because wax vapour, oxygen and heat are present. The flame uses oxygen inside the glass; when there is too little, the flame shrinks and goes out. The wax did not simply disappear: it changed into new gases and soot.
Fire is not just heat
It is reasonable to think that adding heat always makes a fire stronger, because a cold match will not light. But heat is only one part of the triangle. Without fuel or oxygen, extra warmth cannot keep the chemical change going and may only warm the surroundings.
Cooking and fire safety
A cooker supplies heat to fuel or electricity so food changes. Firefighters stop fires by removing one side of the triangle: water cools, a blanket blocks oxygen, and clearing dry plants removes fuel. Never test fire ideas alone; use them with an adult and follow local safety rules.
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