A submarine has a large ballast tank, which controls its position and depth from the surface of the sea. So, a submarine submerges by letting water into the ballast tank. This is because its weight becomes greater than the buoyant force and hence it goes below water.
Air in the atmosphere exerts buoyant force on any object such as a hot air balloon that rises and floats. The hot air balloon descends when its weight is higher than the buoyant force and becomes stationary when the weight equals the buoyant force.
A ship floats on the surface of the sea because the volume of water displaced by the ship is enough to equalize the weight to the weight of the ship. The hollow shape of the ship makes the overall density of the ship lesser than the sea water. So, the buoyant force acting on the ship is large enough to support its weight
Certain group of fishes uses Archimedes’ principle to go up and down the water. Fishes fill its swim bladder (air sacs) with gases to rise to the surface. The gases diffuse from their own body to the bladder and thus making the body lighter thus, enabling the fishes to go up.
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