If the buoyant force acting on a body submerged in a liquid,say water, does not depend on depth, why does it become increasingly difficult to push an object deeper and deeper. I know that the buoyant force is just the pressure difference between the bottom and the top of an object, and since the only forces acting are the force F( which you are applying on the body to push it) , the buoyant force and the weight of the object and also since the latter 2 are constant shouldn't F also be constant? Could someone please point out to me where i am going wrong?
Answer
The force required to push an object into water increases as the object submerges, i.e. as the amount of water the object displaces steadily increases. But I think if you do the experiment carefully you will find that, once the object is fully submerged, the force required should be almost constant.
Thereafter, many objects get easier to push down with increasing depth, as the water pressure crushes them and they therefore displace less water. Wetsuits, for example, become greatly less buoyant with depth for this reason, which is why divers usually wear a buoyancy compensator.
At extreme depths, if something is less compressible than water, it will become harder to push down owing to the increasing density of water with depth. Factors such as this are important in the design of deep sea submersibles and bathyscaphes such as Alvin and the Trieste.
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