Question

Give a reason for the following: 

(a) The cork floats while the nail sinks when both are placed on the surface of the water. 

(b) You feel lighter when you swim. 

(c) It is easier to walk on soft sand with a flat shoe than a pencil – heeled shoe.

Answer 1

(a) The density of cork is less than that of water, whereas the density of a nail is greater than that of water. A substance whose density is less than a liquid will float on the surface of that liquid. Thus, a cork floats in water. On the other hand, a substance whose density is greater than that of a liquid will sink in that liquid. Thus, a nail sinks in water. 

(b) We feel lighter when we swim, due to buoyancy upward force which is acting on our body by water 

(c) The larger area of flat shoe exerts less pressure as compared to the pencil heeled shoe. Due to greater pressure, the sand under pencil-heeled shoe sinks in greater depth and therefore, it is difficult to walk with a pencil- heeled shoe on the sand. On the other hand, flat shoes exert less pressure and do not sink down in the sand.