☰ Year plan · Science

Burning needs air

Week 1 · Chapter 1 Conditions for Burning: 1-1 How Things Burn and Air; 1-2 The Role of Oxygen · 3 lessons
1

Why a flame needs fresh air

Science P6: Term 1, Chapter 1, pp. 6–11
GoalExplain why a flame needs fresh air to keep arriving, and predict what happens in three jar set-ups.
New words
fuel · something that can burn, such as wood, wax or gasflame · the glowing, hot part of a fire where gases burnfresh air · new air that keeps coming in to replace air that was already used
Explanation

Burning needs three things at the same time: something that burns (a fuel), enough heat to start it, and air. A candle’s wax is the fuel, and the flame is where hot wax gas burns. Air is not just empty space. A flame uses part of the air, so new air must keep arriving, and the hot used gases must be able to leave. Think of a crowded bus: people can only get on if others get off. Grown-ups sometimes show this with a candle under a glass jar. With a tight lid, the flame soon dies down. With a gap only at the bottom, air cannot flow through the jar, so the flame does not last long. With gaps at the bottom and at the top, fresh air comes in low and warm gases leave high, so the flame keeps burning. Children never do this test: an adult shows it, or you watch a video and make predictions.

Jar set-upCan air flow through?Flame (usual result)
Tight lidNoDies down quickly
Gap at the bottom onlyHardlyDoes not last long
Gaps at bottom and topYes, in and outKeeps burning
Worked examples
fancoals
At a barbecue, a grown-up fans the charcoal and the coals glow brighter. The fan pushes fresh air onto the coals, so the burning goes faster.
A camping stove inside a closed tent is dangerous: the flame needs fresh air, and burning without enough air can make a poisonous gas. Tents and rooms with fires must always have air flowing.
Salma predicts what happens in a jar with gaps at the bottom and top. She says: air enters low and leaves high, so the flame keeps burning. Her prediction uses the idea of air flow.
Class activity

Predict and draw. With a grown-up, draw three jars. For each one, draw arrows showing where air can go in and out, then write what you expect the flame to do. Your teacher or a video will show the real result. Were you right? Safe tries: blow gently across a strip of paper and wave a paper fan in front of your face. No matches or candles for children.

Practice
1
Name the three things burning needs.
2
Why does a candle’s flame die down in a jar with a tight lid?
3
Which jar keeps the flame burning longest? Say the letter.
JarGaps
Anone, tight lid
Bbottom only
Cbottom and top
4
Why must a room with a charcoal heater have fresh air?