Electromagnetism is one of the four fundamental forces of nature. The others are gravity, and the strong and weak interactions of particle physics. The electromagnetic force pushes or pulls anything that has an electric charge, like electrons and protons. It includes the electric force, which pushes all charged particles, and the magnetic force, which only pushes moving charges. There are two types of electric charge: positive and negative. The electric force pulls opposite charges (positive and negative) towards each other. It pushes similar charges (both positive, or both negative) away from each other. What is a field? The electromagnetic force comes from something called an electromagnetic field. In physics, a field is how we keep track of things that might change in space and time. It is like a set of labels for every point in space. For instance, the air temperature in a room could be described by a field, where the labels are just numbers saying how hot it is at that point in the room. We could have more complicated labels as well. On a map of wind speeds, the label could be...