Can someone explain this in terms of apparent weight of the body or law of floatation and NOT in terms of an equation of oscillation?
[Physics] When a body just floats on a liquid (density of body and liquid being equal) and a force is applied on the body, it oscillates. Why
buoyancy
Best Answer
This sort of example is done when the volume of fluid displaced by the object can change.
So the object is floating in the fluid with some of it not immersed in the fluid.
The theory goes that the object if floating in the fluid with the upthrust due to weight of fluid displaced by the object equal in magnitude but opposite in direction to the weight of the object.
That is the equilibrium position.
Now the object is displaced downwards so that the weight of fluid displaced (the upthrust) increases so there is now a net force on the object upwards towards the equilibrium position or the object is displaced upwards so that either the weight of fluid displaced (the upthrust decreases) so there is now a net force on the object downwards towards the equilibrium position.
So in both cases there is a force which moves the object back towards the equilibrium position and then, with light damping, you have oscillatory motion.
If the density of the fluid is equal to the density of the object then to balance the weight of the object and the upthrust the object has to be totally immersed.
Push the object down does not change the upthrust and so the net force on the object will still be zero and it will move downwards until viscous forces stop it.
There is a possibility of something slightly different in that the object could be lifted partially or totally out of the fluid.
Then the weight of the object will exceed the upthust and the object will have a net downward force.
Unfortunately when the object becomes totally immersed in the fluid the weight and the upthrust will be equal and so there will be no net force on the object. In particular it will not have a opportunity to reverse its motion and move back up towards where it started from.