 Now, we introduce mechanical energy. Conceptually, what we're talking about here is that there are many different forms of energy. But we can group those many different forms of energy into related categories. And one of those categories looks at the several type of energy that all relate to mechanical forces in motion. So any of those types that relate to those mechanical forces in motion, we're going to call those mechanical energy. Now, we can use several symbols to stand for mechanical energy. So for example, you could use an E with the subscript MeCH to let that know that that's the mechanical forms of energy. Some books actually use an Me to describe mechanical energy, while some just use a capital E to describe that mechanical energy. Now, there's some basic types of mechanical energy that we'll want to take a look at here. The first one being kinetic energy. And kinetic energy, again, is the energy of motion. So any object which is moving will have some mechanical energy, because it will have some kinetic energy. The other main type of mechanical energy is potential energy. We could think of this as a stored energy. So any time you've got some sort of a mechanical force and you've got energy stored, so that as soon as you release that object, that mechanical force is going to convert that stored energy into energy of motion or some other forms. We consider that a mechanical energy as well. There's two main types of potential energies that we've looked at so far in our introductory physics course. And that's the potential energy from gravity and the potential energy from springs. If we kind of put this all together and we look at the symbols that we've been using, we can define an equation which tells us that that mechanical energy is really a total of the energy we have in each one of these forms. So we look at the kinetic energy plus the potential energy due to gravity plus the potential energy due to the springs. All of those things combined together gives us our total mechanical energy. Not all energy is mechanical. And so as we look at those basic forms of mechanical energy, it's helpful to think of the fact that not all the energy we're dealing with is in mechanical form. So for example, chemical energy, thermal energy, nuclear energy, and electromagnetic energy are some other categories that we'll study at different points in physics that are definitely not mechanical in nature. Now I want to point out there are some other non-mechanical forces and non-mechanical energies. This is not an exhaustive list. So this just introduces you to the basic concept of mechanical energy.