Amain difference between gravitational and electric forces is that electrical forces
a) attract.
b) repel or attract.
c) obey the inverse-square law.
d) act over shorter distances.
e) are weaker.

B) repel or attract

Explanation:

Gravitational forces and electric forces are very similar in many aspects, however they also have some differences.

Concerning similarities, we can see that their formula is quite similar:

where G is the gravitational constant, m1 and m2 the masses of the two objects, r the separation between the two objects, k the Coulomb's constant, q1 and q2 the charges of the two objects. We see that both forces obey an inverse-square law, since they both depend on .

However, there is one big difference between the two forces. In the formula, m (the mass) can only be positive, while q (the charge) can be either positive or negative. As a result, we have:

- The gravitational force can only have one sign --> in fact, it is always attractive

- The electric force can have 2 different signs --> in fact, it can be both attractive or repulsive (in particular, it is attractive when the charges have opposite signs, and repulsive when the charges have same sign).

answer(20) psi;