Question

why warm air is lighter than cold air

Answer 1

Hot air is less dense than cold air ,amusing that volume is less constant.Because the molecule in the heated air move more and faster than in cold air.Think about a room filed with people.If the people move round quickly (as molecules in heated air),then the people will spread out more and make more room between eachother(which would be lower density).Since the hot air is less dense and more dense object are "more affected" by gravity .Then the warm air is lighter.

Answer 2

Hot Air is lighter than Cold Air simply because it exerts less Pressure..................