manual

30
Air expands with heat and contracts when cooled.
hot,
light air
cold,
heavy air
The air particles move around
a lot when it’s hot and occupy
a lot of space (the volume of
air, or any gas, is greater
when heated).
The air particles move more slowly
when it’s cold and take up less
space (the volume of gas is less
when cooler).
A hot air balloon rises when the molecules of gas
inside the balloon are heated. This increases the
volume of the gas inside the balloon and therefore
lowers the overall density of the air inside. So, the less
dense air inside ”floats” on the more dense air outside
and the balloon rises.