SIMPLIFIED: "5.1: Coulomb's Law"

Link: https://phys.libretexts.org/Bookshelves/Electricity_and_Magnetism/Electromagnetics_I_(Ellingson)/05%3A_Electrostatics/5.01%3A_Coulombs_Law 

Note: The above image is from the original article

The article linked above talks about Coulomb’s Law! Coulomb’s Law includes an equation that allows you to calculate the force between two charged objects. An object can either be positively charged, negatively charged, or neutrally charged. When dealing with Coulomb’s Law, we are only going to be dealing with positively charged and negatively charged objects. This is because if an object is neutrally charged, it means it has 0 net charge. There might be both positive and negative charges inside of the object, but they will cancel each other out so that the resulting charge is neutral, or 0. 

Now, here is the equation that is based off of Coulomb’s Law:

The Coulomb’s constant, which is what k represents, is the same number every time. The value of k is 9 times 10⁹. No matter what type of problem you are solving regarding electrostatics, if you see that letter k, you need to plug in 9 times 10⁹ into your calculator. The equation also includes the two charges. To calculate the force between two charges, you need to plug in the values for each charge, and also the distance between the charges. The equation does make sense mathematically; if you increase the distance between the two charges, the force between them will decrease. However, if you increase the value of each charge, then the force between them becomes stronger.

We also need to talk about the signs for the charges. When specifically calculating the force, it does not matter if the charges are positive or negative. You should just plug in the absolute value of the charges into the equation regardless of if it is positive or negative. However, the charge being positive or negative is still important. This is because of the fact that opposite charges attract and like charges repel. Therefore, if you have two positive or two negative charges, then they will repel each other. On the other hand, if you have one positive charge and one negative charge, then they will be attracted to each other. Whether the two charges repel or attract, the magnitude of the force between them does not change, which is why I said that you should just plug in the absolute value of both charges into the equation earlier in the paragraph. You only look at if the charges are positive or negative to determine the direction of the force; if the signs of the two charges are the same, then the force on each charge is directed away from the other charge, but if the signs of the two charges are different, then force on each charge is toward the other charge.