Hot air balloon rise in the air due to the property of
buoyancy possessed by all liquids and gases including the atmospheric air. The air in
the atmosphere tries to push up any object that is present in the atmosphere. This
pressure is equal to the weight of volume of air equal to the volume occupied by the
object. A hot air balloon has a very large balloon filled with hot air. This hot air
lighter than the atmospheric air at normal temperature. As a result the weight of the
balloon with the hot air inside it is less than the weight of same volume of atmospheric
air. This means that that downward force acting on the balloon due to force of gravity s
less than the upward force of buoyancy. This causes the balloon to rise up in the
air.
However it is worthwhile noting that as the balloon
moves up the atmospheric air around it becomes less dense, causing the net upward force
of buoyancy to decrease. When this becomes zero the balloon does not rise up
further.
To lift a total load of 500 kilograms in an air
balloon it will be necessary to ensure that the volume of air in the balloon and its
temperature is such that the weight of hot air in the balloon will be at least 500
kilograms less than equivalent volume of normal atmospheric air.
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