 Okay, this is going to be a relatively short section. I am going to talk about material objects, also known as matter, and the fact that they have certain amounts of energy associated with them. I have a very informal definition of energy. This is just a definition that I made up. Energy is the ability that a piece of material has that can be used to do work. And I have a very informal definition of what work is. The ability to push, pull, lift, or move other materials around. So what I am telling you is that material objects have certain amounts of abilities to push or pull or lift or move other materials around, and that ability is called energy. Again, this is a very informal definition. You're not going to find it in a very technical science book or even in Wikipedia, but it's reasonably accurate. The other punchline that I want you to realize is that different pieces of material, different pieces of matter, have different amounts of energy. So the idea is that some materials have a lot of energy, some not so much. Depends on the material, depends on what it's made of, depends on how fast the material is moving around, and I'll give you some examples. Here's a picture. You may or may not know what this is, but this is a bomb. In fact, it is the first, I think it's a replica of the first atomic bomb. So it's a piece of matter, right? It's matter, it's a material object, and it had so much energy associated with it that it made a huge explosion. This over here, you may not be able to figure out what it is because it's a cartoon, but these are pieces of wood. They also are material objects, and they also have certain amounts of energy associated with them. Maybe not as much as you could get out of the bomb, but these pieces of wood, or if they were real, they have energy associated with them too. You can get the energy out of these things. One way of getting energy out of these things is to set them on fire, and then they will release heat, and that is energy, because heat can push, pull, and move things around. So that's my introduction to what energy is, and my introduction to the fact that different material objects have different amounts of energy associated with them. Traditionally, people think of energy as coming in one of two forms. So there are two kinds of energy. The first kind, again, very informal, is called potential energy. You should think of that as energy that is stored inside of a piece of material, but it's not currently being used. The best example of that is the logs, again, or these pieces of wood. Imagine that they're sitting by your fireplace. They have potential energy. The way that you could release that energy one way, again, is to set them on fire, and then these pieces of wood would lose some of their potential energy because you would have released it. But potential energy is energy that's just inside of a piece of material not being used. That's type number one for energy. Type number two for energy is called kinetic energy, and that is energy that a piece of material has because it's moving. So the best example is probably shown here. Here's a baseball player, this baseball here. It was moving. It was moving very fast, and because it was moving very fast, it had a certain amount of kinetic energy, and it gave some of that energy to that guy's face. So that's an example of kinetic energy. If the ball was moving faster, it would have more kinetic energy, and it would do more damage to that guy's face. If it was moving more slowly, then it would have less kinetic energy, and it would do less damage. So that's basically the ideas behind the two types of energy. Potential energy, energy not being used, kinetic energy, energy that something has because it's moving. And just to give you a couple of examples, here, this is something I usually ask my students, does this car have kinetic energy? You can pause at each question and think about it, but assuming that this car is moving and it kind of looks like it's moving because the background is blurry, then yes, this car has kinetic energy. Does the car have potential energy? Sometimes, again, you can pause if you want to think about this, the answer is going to be yes as well. Sometimes that's a little bit more difficult for students to understand, but the idea is that this car is not using all of the energy that it could possibly use. It could be moving faster, or even if it was going at top speed, this may sound ridiculous, but you could set the car on fire while it was moving at top speed and you'd release even more energy. So if there is more energy that you can get out of a piece of material, then it's got at least some potential energy. Here's a different situation. Again, same kind of questions you can pause and answer if you like. How does this car have kinetic energy? For our purposes in this course, I'm going to say no, because it's not moving, or at least it doesn't look like it's moving in this picture. Now, technically speaking, yes, it does a little bit because even though you can't see it, the atoms and the molecules that make up this car, they're jiggling around a little bit. They are moving a little bit. It has a little bit of kinetic energy, but not enough that we're going to be concerned about it. Does the car have potential energy? Again, you can pause, but the answer is going to be yes, because you could move this car around and you'd be basically giving that car some kinetic energy. So because you can release energy from this vehicle, it definitely has potential energy. Like I said, there's a lot of math behind energy and calculating how much energy things have because you can basically put a number on how much energy something has, then energy also has units associated with it because you can numerically describe how much energy something has. The most common units that are used, at least in science, are the following two units. We're going to use them a lot in the coming sections. The first most common unit is something called a jewel. It's spelled a little bit differently than maybe the jewel that you might think of. Most people, when they hear the word jewel, they think of diamonds and rubies and things like that. That's not what we're spelling here. That's not what we're talking about. We're talking about a unit for measuring energy called JOLE. That's one of the more common units that's used in science for measuring energy. You can put prefixes onto jewels as well. There are kilojoules. That's 1,000 regular jewels. There are milli-joules. That's one-one-thousandth of a jewel, etc., etc. You can put any of the metric prefixes onto jewel as you could put it onto grams or liters or whatever. So you should know that jewel is a measure of energy. The other most common unit for measuring energy you probably have heard of is called a calorie. When you hear people talk about calories and food, they are basically talking about how much energy is stored inside of the food. Again, you can bundle calories together and 1,000 of them bundled together. It's called a killer calorie. There are milli-calories, etc. So you can put the same prefixes onto calories. As I mentioned, the word calorie shows up when people discuss food a fair amount, but it's just a measure of energy.