Take an empty plastic bottle . Close the mouth of the bottle with an airtight stopper . Put it in a bucket filled with watere . The bottle floats .
Push the bottle into the water. You feel an upward push. Try to push it further down. You will find it difficult to push deeper and deeper. Water exerts a force on the bottle in upward direction. Now release the bottle. It bounces back to the surface.
Does the force due to the gravitational attraction of the earth act on this bottle? If so, why doesn't the bottle stay immersed in water after it is released ?

Explanation

Yes. The force due to the gravitational attraction of the earth acts on the bottle in the downward direction. The upward force exerted by water on bottle is greater than the downward force mg and hence the bottle does not stay immersed in water, but floats