CBSE - VII - Science - Heat
when we blow the flame of a candle it goes off. but sometimes to make a fire we have to blow air on it. why does this happen
- Pressure difference which is created by the blowing carbon dioxide near the fire plays a vital role towards making of the fire.
- The blowing carbon dioxide has greater velocity than the atmospheric air
- This causes to lower the pressure of air near the fire,
- Applying Bernoulli’s theorem which states that pressure is inversely proportional to the velocity.
- The pressure difference causes nearby atmospheric air to rush towards the fire, thereby supplying the oxygen mixed in that atmospheric air.
- Oxygen is very good supporter of combustion, but it should be noted that oxygen is not a combustible gas itself.
- With large amount of oxygen mixed in atmospheric air being blown towards fire, the fire glows exceedingly.
- That is why to make small amount of fire slight blowing of air is done.
- But if the blown air has a comparitively larger velocity, then it completely displaces the air and heat blanket from the point of fire, which is required by the fire to sustain itself.
- Thus if the air is blown with a higher velocity, the fire goes off.
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