The way charges attract or repel each other can be described as a force. A charge can exert a push or pull on another charge depending on if the charges are positive or negative. How much force they exert can be figured out using Coulomb’s Law of Electric Force, which is:

where  C = 8.99 x 10⁹ Nm²/C²

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Now Coulomb’s Law looks a lot like Newton’s Law of Gravitation… they both have a constant out in front, and they both have the inverse square relationship relating distance to force. They are different, however in a couple of important ways. Newton’s Law of Gravitation breaks down on the atomic level, and has to be replaced with Quantum Mechanics. Also, gravity is only an attractive force, whereas electric forces are both attractive and repulsive.

Notice the inverse square relationship: if you double the distance two charges are standing apart, the electrical force felt by the charges will decrease by a factor of four. If you triple the distance, the force goes down by a factor of nine.

Teachers and students both like to study, teach and learn subjects in neat, separate little packages, but this isn’t the way the universe works. Things aren’t usually isolated in their own box so they nothing to do with anything else. When we learned about the inverse square law, it wasn’t only for Newton’s Law of Gravitation… it popped up here also! And Newton’s Laws included forces, acceleration, gravity and energy, and now we’re going to add in an electrical force. But what does electrical force have to do with Newton’s Laws?

Click here to go to next lesson on Coulomb’s Law and Newton’s Laws.

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