WEBVTT

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All objects have a mass.
The greater the mass, the greater the weight.

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Weight is the gravitational force
that pulls an object downwards.

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But if we plunge an object in water, its weight seems less,
as if the object had become lighter.

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In fact, its mass, and therefore
its weight remain the same.

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However, a new force counteracts the weight.

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This force is called the buoyant
force or simply buoyancy.

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The object experiences
the combined action of both forces.

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If the buoyant force is less than the weight,
the object falls, it sinks.

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Inversely, if the buoyant force is greater
than the object’s weight, it goes up.

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The object floats when these two forces are balanced.

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In any case, buoyancy is oriented upwards.

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Would it be possible to increase this force
enough to make a heavy object float?

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The answer is « yes! »

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The Greek scholar Archimedes found the solution.

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A body immersed in a fluid whether
fully or partially immersed

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is equal to the weight of
the fluid that the body displaces

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Let’s consider an example. When an object
sinks in water, it displaces water.

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The volume of water displaced is equal
to the immersed volume of the object.

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The bigger the object, the more water is displaced.

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Archimedes asserted that the weight of the volume of
water displaced is exactly equal to the buoyant force


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except that this force goes upward.

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For buoyancy, the shape is as important as the mass.

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A compact mass displaces very little water, whereas
a ship, given its shape, displaces a lot of water.

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The greater the immersed volume, the greater
the intensity of the buoyant force.

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Thus, a light object can sink whereas
a very heavy object can float.