Question

when water is drawn from well with bucket weight of bucket with full water appears lighter until it comes to surface of water in well.this is due to

Answer 1

This is due to the buoyancy force exerted by water (all liquids) on the bucket in the upward direction. So the effect of bucket's weight is reduced.

This principle is called Archimedes principle. The weight of the bucket full of water, is reduced by the weight of water of the same volume as that of the bucket.