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Name: Kailey Joy M.
Status: student
Age: 10
Location: N/A
Country: N/A
Date: Saturday, April 20, 2002 8:17:44 PM
Question:
When I exhale, why is my breath warm when my mouth is wide open but is cold when my lips are puckered?

Replies:
Kailey,

Whenever a material expands, it cools of. IF you breathe with your mouth wide open, the air from your mouth comes out just as it is in your lungs. There is no compressing or expanding. It is warm. When you pucker your lips, the breath is compressed within your mouth: the air atoms are squeezed more tightly together than usual. As it leaves your mouth, the air expands. It gets less tightly packed. This results in a cooling. The more strongly you blow, the more tightly packed becomes the air in your lungs and mouth. Blowing harder then results in more expanding and cooling as the air comes out.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


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