Question

a ball appears to be lighter as long as it is in water than when it is outside water. Why ??

Answer 1

This problem will be completely governed by the law of buoyancy.The experiences more buoyant force in water than that in air.When the ball is in the water the buoyant exerts an upward force due to which we feel like the ball becomes  lighter when it in water.

Answer 2

when an object floats on water it means the buoyancy force is more than the gravitational force . as buoyancy force acts in upward direction and gravitational force acts in downward direction the ball feels to be lighter in water than in air .