Why does a hot air ballon fly?

Hi Kate36,
  
"The physics behind why a hot air balloon flies involves the
principles of density and buoyancy. When air gets hot, it expands. As
the hot air molecules spread out the total volume of air increases
making it less dense then the surrounding air. It then follows
Archimedes' principle which states that an object is pushed upward
with a buoyant force equal to the weight of the fluid it displaces.
Just like a piece of ice is pushed up by the surrounding water, a hot
air balloon is pushed up by the surrounding air. We say that it
becomes buoyant because the hot air displaces more than it's own
weight in the surrounding cooler air."
http://www.ktca.org/newtons/newtonsclassics/classic2.html
  
  
On the Howstuffworks website, it explains very well using photos and
illustrations how and why a hot air balloon can fly. Below are the
links to the relevant pages.
  
Introduction to How Hot Air Balloons Work
http://travel.howstuffworks.com/hot-air-balloon.htm
  
Balloon Design
http://travel.howstuffworks.com/hot-air-balloon1.htm
   
Piloting a Balloon
http://travel.howstuffworks.com/hot-air-balloon2.htm
   
Launching and Landing
http://travel.howstuffworks.com/hot-air-balloon3.htm
   
Wind and Weather
http://travel.howstuffworks.com/hot-air-balloon4.htm
    
Air Pressure + Gravity = Buoyancy
http://travel.howstuffworks.com/hot-air-balloon5.htm
    
Lighter than Air
http://travel.howstuffworks.com/hot-air-balloon6.htm
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Hope you find this information useful.
  
  
  
Search terms: [ "a hot air balloon flies" ]

Eureka!  What would have happened if Archimedes dried his towel over a
after he got out of his apocryphal bath?  Would he have seen that the
relative density within a gas is similar to what he discovered about
liquid?