Answers

2014-09-26T11:14:00+05:30
Low density substance can float  over the high density substance, and the density of hot gases are lower than cold gases,that is why  hot gases move upward and cold gases move downward.
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hot sases moves upeards because .. as the air molecules are heated they began to spread ie volune increase and volume is directly proportional to mass hence as the mass gets decrease.... and at last the hot air will be lighter than air hence it moves up and vice versa on cold air
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2014-09-26T11:15:41+05:30
Hot gases are lighter than cold gases as their constituent particles have more kinetic energy than the particles of cold air. Hence, the molecules of hot gases take up more space and this makes the hot gas less denser and lighter.
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