Video narration
What controls how strongly two electric charges attract or repel? A rubbed balloon pulling paper pieces shows the idea: charge creates force at a distance. For two stationary point charges, Coulomb's law gives the magnitude: F equals k times the absolute value of q one q two, divided by r squared. q one and q two are charges, r is separation, and k is the Coulomb constant-about 9 times 10 to the 9 newton metre squared per coulomb squared in air or vacuum. The formula gives size; signs give direction. Like charges repel; unlike charges attract. More charge means more force. But here's the surprising turn: distance is squared. Double the separation, and the force becomes one-fourth-not half. That's the inverse-square law. So what controls it? Both charges and separation. Use Coulomb's law for size, then the signs for attraction or repulsion. Distance has stronger effect.