How come you need to blow on a flame to help it grow into a fire, but if you blow on a candle, it blows out?
In: Physics
If you blow too hard on too small a flame, it will go out too. But a fire has much more fuel available to it than a candle. That’s the key.
A flame is the area where hot flammable gas mixes with air and burns. Too much air too fast blows that gas away from its source, cooling the source off and stopping the fire.
But *a little bit* of air can help the gas react quickly and efficiently, which helps keep the source hot.
A fire needs 3 things – fuel, oxygen, heat.
By blowing on a fire you are adding oxygen but taking away heat.
A bigger fire has plenty of heat so it can take your extra oxygen without cooling down too much.
A tiny flame like a candle doesn’t have much heat, so you blowing on it cools it down too much and it goes out. This is also true if you blow too hard on a fire that is just starting.
To turn a flame into a fire with breath you are gently encouraging heat to move from a small area of fuel to other nearby areas of fuel before the heat source runs out of fuel and dies.
A candle, in contrast, has plenty of fuel in the wax and is in no danger of burning out in the short term. To put it out without waiting you swiftly blow the heat and flame away away and cool the embers and wax enough that the flame does not return when the airflow ceases.
Latest Answers