Which statement about electric force and gravity is correct?

Which statement about electric force and gravity is correct?

• A. Electric forces are weaker than gravity.
• B. Electric forces are of no consequence at small scales.
• C. Electric forces are greater than gravity.
• D. Gravity dominates at all distances.

Answer: (C)

Electric and gravitational forces both follow inverse-square laws, but their strengths differ by an enormous factor. The electric force between two charges is F = k q1 q2 / r^2, while the gravitational force between two masses is F = G m1 m2 / r^2. Because of this, the ratio of the electric force to the gravitational force for typical tiny charges and masses is enormous. For two protons, or for charges on the scale of the elementary charge, the ratio F_e / F_g works out to about 10^36, so the electric interaction is vastly stronger than gravity at the same separation. This is why electric forces are the dominant interaction at small, atomic, or molecular scales. Gravity, while always attractive and accumulating over huge masses, is incredibly weak on these scales. At very large, neutral scales (like planets and stars), gravity becomes the controlling force, but that doesn’t negate the fact that, for typical charged particles, electric forces far outweigh gravity.

Electric and gravitational forces both follow inverse-square laws, but their strengths differ by an enormous factor. The electric force between two charges is F = k q1 q2 / r^2, while the gravitational force between two masses is F = G m1 m2 / r^2. Because of this, the ratio of the electric force to the gravitational force for typical tiny charges and masses is enormous. For two protons, or for charges on the scale of the elementary charge, the ratio F_e / F_g works out to about 10^36, so the electric interaction is vastly stronger than gravity at the same separation.

This is why electric forces are the dominant interaction at small, atomic, or molecular scales. Gravity, while always attractive and accumulating over huge masses, is incredibly weak on these scales. At very large, neutral scales (like planets and stars), gravity becomes the controlling force, but that doesn’t negate the fact that, for typical charged particles, electric forces far outweigh gravity.