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).

this is poiselle's equation from fluid mechanic in physics. mech eng