# Clever people

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18 years ago
#21
(Original post by NikNak)
I know but if you can have two pockets of air that are the different densities but are the same pressure (obviously the volumes would be different).
if the air in the ballon is a higher temperature then the volume of the air MUST decrease in volume for the pressure to remain the same of the outside of the ballon. This means the air inside the ballon would be less dense and so it rises?
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18 years ago
#22
(Original post by NikNak)
I know but if you can have two pockets of air that are the different densities but are the same pressure (obviously the volumes would be different).
yes, one's molecules would be moving faster than the other's
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18 years ago
#23
Heres the actual Q Ive got

WHATEVER THE TEMPERATURE OF THE AIR IN THE BALLOON, ITS PRESSURE WILL BE THE SAME AS THE SURROUNDING AIR.
EXPLAIN WHY.

Thanks everyone, im really grateful

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18 years ago
#24
(Original post by NikNak)
if the air in the ballon is a higher temperature then the volume of the air MUST decrease in volume for the pressure to remain the same of the outside of the ballon. This means the air inside the ballon would be less dense and so it rises?
yes
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18 years ago
#25
(Original post by elpaw)
yes
so thats the answer for the unreg dude?
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18 years ago
#26
NOOOOOOOOOO!! Im not that Unreg.maskall person, urgh

Im just a confused physics student!!! So cud erm, someone summarise an answer for me then!! PLEASE!!!
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18 years ago
#27
(Original post by NikNak)
so thats the answer for the unreg dude?
probably
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18 years ago
#28
(Original post by Unregistered)
NOOOOOOOOOO!! Im not that Unreg.maskall person, urgh

Im just a confused physics student!!! So cud erm, someone summarise an answer for me then!! PLEASE!!!
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18 years ago
#29
(Original post by Unregistered)
NOOOOOOOOOO!! Im not that Unreg.maskall person, urgh

Im just a confused physics student!!! So cud erm, someone summarise an answer for me then!! PLEASE!!!
have the decency to do it yourself seeing as theyve given you the answer.
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18 years ago
#30
please, i promise u. Im not that annying kid who gives abuse
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18 years ago
#31
(Original post by Unregistered)
NOOOOOOOOOO!! Im not that Unreg.maskall person, urgh

Im just a confused physics student!!! So cud erm, someone summarise an answer for me then!! PLEASE!!!
K, so the air in the ballon increases in temp, and expands. The pressure remains the same inside and out because the volume of air inside the ballon decreases. So although the pressure is the same, the volume of air inside the ballon is lower.
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18 years ago
#32
(Original post by NikNak)
K, so the air in the ballon increases in temp, and expands. The pressure remains the same inside and out because the volume of air inside the ballon decreases. So although the pressure is the same, the volume of air inside the ballon is lower.
no, the volume increases.
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18 years ago
#33
Hmm, ok.
so how comes the volume of air decreases. How does this happen?
Thanks for replying by the way.
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18 years ago
#34
(Original post by elpaw)
no, the volume increases.
oh yeah sorry....
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18 years ago
#35
(p*V)/T = const.
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18 years ago
#36
Hot air balloons thrust can be found using Archimedes' principle.

The air is heated so it is less dense we are agreed. Its pressure is the same at the hole in the bottom agreed.

^ - z direction

dp/dz = (rho) x g - outside (inside is more complicated)

obviously the pressure gradient would be different if the balloon was solid but the balloon is pressurised by the air outside because the the baloon cannot support a stress. So is the same. Agreed???

The balloon floats because the density of the air inside is lower than outside so the balloon weighs less than the air around it:

F = (rho) x volume - weight

where the volume and weight refers to the balloon and basket and the air in the balloon.

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