Stuff that moves has energy by virtue of the fact that it’s moving. Although it’s hard to say what energy really is, we know it when we see it, and movement definitely counts. In this tutorial we’ll do a little bit of algebra to get from our basic definition of energy to figuring out how much energy a moving thing has, exactly. This is really going to help a lot when we get on to looking at light and photons. Honest.
Before we start looking at light, let’s break down some of the key concepts involved in understanding light. We’ll start here with energy; a term that is rigorously defined in physics and yet nevertheless impossible to fully grasp. In fact, it’s surprising how many things in physics, or indeed in life, are possible to define and yet impossible to grasp. At least being able to define a thing is better than bandying about words without having any clear agreed definition — we’ll leave that to philosophers. At least for now.