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Falling and Rising

Galileo explained falling and rising bodies with two forces: gravity and buoyancy.

Every child knows that a stone will fall, while smoke from a fire will rise. Explaining why this happens is not so straightforward.

Since the time of Archimedes, scientists knew about buoyant forces that were exerted on an object immersed in water. In the 17th century AD, Galileo realized that bodies in air also experience buoyant forces that oppose the pull of gravity. If the buoyant forces overcome gravity, then the body will rise. If gravity is stronger, then the body will fall.

As well as buoyancy, a body that moves through a fluid also experiences forces of resistance. For a falling body this air resistance opposes gravity. Air resistance is complicated and depends on the shape and density of the falling object.

It is differences in these forces that oppose gravity that account for different behaviour of falling objects.

Gravity itself acts on all objects in exactly the same way, no matter whether heavy and light.


City skyline with balloon

Parachute
magnifyParachutes fall, while balloons rise.
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