Science of Conflict

Buoyant force

When an object is placed in a fluid a force, called the buoyant force, acts to push the object upwards. The strength of the force is equal to the weight of the volume of fluid displaced by the object.

It is the objects volume, not its weight that determines the buoyant force.

Take a submarine, for example, the buoyant force acts to push it to the surface while the weight of the submarine acts to push it to the bottom. The strength of these two opposing forces determines if the sub rises or sinks in the water.


A submarine however, can only control its weight, since the buoyant force can only be adjusted by a change in volume. This is unlikely to happen since the hull is inflexible and designed to withstand high water pressure that would crush it at great depths.

A submarine sinks if it takes in water to increase its weight (force acting downward). It will rise if it expells water from its tanks, therefore making itself lighter.

As it rises, the buoyant force is greater than the force acting to push it down (weight).

As it sinks the force pushing it down (weight) is greater than the buoyant force pushing it up.

1) How can a submerged submarine increase the buoyant force acting on it?

2) Is this practical? Explain.

3) How can a submarine, floating on the surface, increase the buoyant force acting on it?

4) How does a submarine use its ballast tanks to sink or float to the surface?

5) The ballast tanks are used to increase the buoyant force acting on t with chemicalhe submarine

6) When submerging with its engines off submarine can adjust its

7) The buoyant force acting on a fully submerged submarine is

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Continue with chemical reactions and camouflage of submarines
Continue with controlling the submarine
Continue with nuclear powered submarines
Continue with buoyancy