Question

why it is easier to lift a heavy stone in water than in air

Answer 1

According to Archimedes principle, a body when immersed in a fluid shows an apparent loss of wieght which is equal to the weight of the fluid displaced by the body.


So a heavy stone when under water, is acted upon by upthrust due to water , which ultimately reduces the true weight of the stone. So, it is easier to lift a heavy stone under water .

Answer 2

it is because water applies a resistance force on stone or u can say up thrust force and density differences also play a major role
For more information check for fluid machines book