TQ 19.7

Similarities:

a. Both forces decrease as the square of the distance between two objects.

b. Both forces depend on the product of intrinsic quantities: mass (gravity) and charge (electric force).

c. Both forces act along the line connecting two objects.

Differences:

a. Gravity is always attractive, but electric force can be either attractive or repulsive.  

b. Electric force is generally much stronger than gravitational force.