Earth has a strong force of gravitation.Though we also exert  a force of gravity towards earth,earth does not move towards us due to its hug mass.But in the case of evaporation water wapour  which have a negligible mass is overcoming earth's attraction and moving upwards.What is the reason for this?

Asked by mythili Suresh | 29th Jul, 2014, 07:58: PM

Expert Answer:

Earth's gravity attracts all objects in it. All objects are pulled towards the Earth by the same amount of force.
However, gravity is a very weak force. Objects can overcome gravity with the help of various external factors.
Example: 1) A feather falls slowly as air resists its fall.
             2) A book held in hand cannot fall down as the hand helps in overcoming gravity.
When water evaporates, the water molecules gains kinetic energy and the temperature rises.
This causes the air containing vapour to become lighter than the colder air above.
Hence, the cold air from above falls down and the air containing vapour rises up. Also, the negligible mass of vapour 
makes it easier for air to rise up and overcome gravity.

Answered by Romal Bhansali | 30th Jul, 2014, 12:09: PM