Question

Why do objects float in liquids denser than themselves ?

Answer 1

If an object were completely immersed in a liquid denser than it, the resulting buoyant force would exceed the weight of the object. This is because the weight of the liquid displaced by the object is greater than the weight of the object (since the liquid is denser). As a result, the object cannot remain completely submerged and it floats. The scientific name for this phenomenon is Archimedes Principle.

Answer 2

Weight of the body = W = downward force acting on the body 
weight of liquid displaced by the body when completely inside the liquid = w = Buoyant force of 
the liquid acting on the body upward 
If (1) W > w , the body sinks 
(2) W < w , the body floats 
(3) W = w , the body remains in equilibrium inside the liquid. 
When the density of the liquid is greater than that of the object, condition (2) is satisfied and hence 
the body floats.