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5. When you blow on the back of your hand with your mouth wide open yourbreath feels warm about if you partially close your mouth form an ``O`` andthen blow on your hand breath fells cool. Why?

5. When you blow on the back of your hand with your mouth wide open yourbreath feels warm about if you partially close your mouth form an ``O`` andthen blow on your hand breath fells cool. Why?

Grade:11

1 Answers

Arun
25750 Points
6 years ago
We can easily explain the   phenomenon if we apply the principles of thermodynamics.

We know that when a gas expands it cools down from thermodynamics. So when you blow air from the mouth it has a higher pressure due to the force of blowing from your lungs. Now the temperature of the air in your lungs is same as that of your body temperature. Therefore, when the air just comes out of the lips it is still hot and compressed. But when it travels a distance from your lips, the gas expands and thus its temperature falls according to the laws of thermodynamics. So you feel a cold blow at a distance. 

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