Question

Which of the following is the weakest force?
A. Nuclear force
B. Gravitational force
C. Electromagnetic force
D. none of these

Answer 1

Hint: There are four fundamental forces that exist in nature, strong nuclear force, weak nuclear force, electromagnetic force and gravitational force. Out of these, the strong nuclear force is the strongest. Among the electromagnetic force and gravitational force, gravitational force is weaker.

Complete step by step answer:
There exist 4 fundamental forces in our universe.
(i) Strong nuclear force
(ii) Weak nuclear force
(iii) Electromagnetic force
(iv) Gravitational force
Let us discuss the four forces.
Strong and weak nuclear forces are the forces between the nucleons (protons and neutrons) inside a nucleus that hold the nucleons together. This is how the nucleus is stable.
Electromagnetic force is the force between bodies having some net charges. Electromagnetic force between two charged bodies can be attractive or repulsive depending on the nature of the net charge on both the bodies. If both the charges are positive or both the charges are negative, then the nature of force is repulsive. For example, the force between the two protons. If one charge is negative or one charge is positive, then the nature of force is attractive. For example, the force between an electron and a proton.
Now we know that two protons repel each other when brought closer due to the electromagnetic force. However, the nuclear force holds them together inside a nucleus. Therefore, the electromagnetic force is weaker than the nuclear force.
The fourth fundamental force is gravitational force. It is the force between bodies due to the masses of the bodies. The nature of this force is always attractive. That is all the bodies in the universe attract each other. However, gravitational force is the weakest force in nature. We can understand the following.
 The gravitational force between two masses (${{M}_{1}}$ and ${{M}_{2}}$) separated by a distance r is given as ${{F}_{G}}=G\dfrac{{{M}_{1}}{{M}_{2}}}{{{r}^{2}}}$, where G is a proportionality constant.
The value of G is equal to $6.67\times {{10}^{-11}}k{{g}^{-1}}{{m}^{3}}{{s}^{-2}}$.
The electromagnetic force between two charges (${{q}_{1}}$ and ${{q}_{2}}$) separated by a distance r is given as ${{F}_{E}}=K\dfrac{{{q}_{1}}{{q}_{2}}}{{{r}^{2}}}$, where K is a proportionality constant called permittivity of free space.
The value of K is equal to $9\times {{10}^{9}}N{{m}^{2}}{{C}^{-2}}$.
If we consider the product of masses and the product of charges equal and compare the values of G and K, we get the gravitational force is weaker than the electromagnetic force. And we already know that the electromagnetic force is weaker than the nuclear forces.
Therefore, gravitational force is the weakest force.
Hence, the correct option is B.

Note: Although gravitational force is the weakest force, for large bodies it dominates over the other three forces. This is because all the charges on a large body cancel out each other and the net charge is zero. Hence, the electromagnetic force is zero. And nuclear forces act only at very short distances. Therefore, the nuclear force is also zero.