Eli5: How can hot air balloons fly by only using fire?
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Temperature is inversely proportional to density as temperature increases, vibration in molecules(for solids and for gases I think it’s kinetic energy(0.5kt^2) and they move faster)increases and space between them increases, decreasing the density. Hot air balloon uses fire to increase the temperature of the air, decreasing it’s density relative to the air around it, there by creating buoyancy (lift or upward force). Air is a fluid just like liquid. Since buoyant force is more than weight (earth pulling stuff towards itself), net force is in the upward direction and the hot air balloon moves up. Same can be assumed for airships filled with hydrogen/helium
Hot air not fire. Hot air rises, cool air sinks. Fire makes the air hot in the baloon. The hotter the air the faster it wants to rise.
It heats up the air in the ballon, which makes it rise above the colder air because hot air is less dense
Heating a gas such as air causes the molecules to move faster. These faster moving molecules push against each other and cause the gas to expand and be less dense. There are fewer air molecules per cubic foot in hot air than in cold air.
Because the air in the balloon is hotter and thus less dense than the surrounding air, it weighs less. Lighter materials float on top of heavier ones, so the balloon rises.
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