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Q & A: Properties of air

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Most recent answer: 09/21/2009
Q:
How can air insulate heat? How can air be compressed? How do you prove that air has mass?
- Lulu (age 11)
Mississauga,On, Canada
A:
1. Heat transfer in still air is mainly by conduction.  The air molecules on the hot side gain thermal energy and then transfer this energy to adjacent ones, and so on, until the heat gets transferred to the cool side.  For air this process is very inefficient.  In a metal or good conductor this process goes very rapidly and so metals are not very good insulators.

2. Air can be easily compressed.  Think of a bicycle pump. You take a volume of air and then just squeeze it into a smaller volume.  The pressure rises. 

3. Easy, you take a container that is leak tight. Weigh it on a scale and then pump the air out and weigh it again.   The weight difference is very small so you need a very accurate and sensitive scale.  You can also think of a hot air balloon.  Since hot air weighs a little bit less than cold air, the balloon will rise like a cork in water.

LeeH

(published on 09/21/2009)

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