Question

A stone dropped from a height falls towards the earth because:
A. The stone exerts a force of attraction on the earth.
B. The earth exerts a force of gravity on the stone.
C. The stone attracts the earth towards itself.
D. The stone repels the earth away from itself.

Answer 1

Hint: According to Newton’s universal law of gravitation, all the masses produce a gravitational field around them in the contact of which, if any other mass comes, that mass will experience a force of attraction towards it. Earth is also a huge mass. Hence if any object comes in contact with this field, it experiences a force towards the earth. This force is the reason why a stone falls on earth when left in air.

Complete step by step answer:
When a stone is dropped from a height, it falls towards the earth. This event proves that there must be a force in downward direction which causes this motion. It is nothing but the weight which causes this motion. The weight is a force by which earth is attracted toward the earth or the stone is attracted towards the earth. This is according to Newton’s third law of motion, which states that to every action there is equal and opposite reaction. Hence the force of attraction of stone towards earth is the same as the force of attraction of earth towards stone. This force of attraction has a value called weight of stone.

Hence all the options are correct, but the most appropriate option (assertion) will be B. i.e. earth exerts force of gravity on the stone.

Note: One might point that if this were true, then why don’t earth moves towards the stone as stone moves towards the earth. Well, earth does move actually. But this motion is so negligible that we can’t detect it. To cause the motion of such a heavenly body, a huge force is required but the weight of stone is too small for this to happen!