# Energy

We can define energy as the capacity to do work and we could further define energy as a scale or quantity.

Let’s say it’s a scale or quantity, that means it’s kind of like mass, it has a particular amount of number and units associated with it, but it doesn’t matter in which direction energy was applied.

The next lesson: Heat, Energy, Work, and Thermal Energy, both lessons are included in Practice Tests.

The following transcript is provided for your convenience.Now a unit for energy is the joule, which actually has a little j, but then when we abbreviate it, it has a capital J. To give you an idea of the unit joule, one joule is the amount of energy used to apply a force of one neutron over a distance of one meter. Notice here it applies both ways force and distance to come up with one single unit. Now you may be thinking I said this was the scale or quantity, so direction didn’t matter. Well that’s true, because say you’re pushing a box and you give it one newton of force, it does matter how far you pushed it, but it doesn’t matter whether you pushed that box north, south, east or west.

That’s what we mean when we say it’s a scale or quantity. It matters how hard you pushed it, but it doesn’t matter in which direction you pushed it. Now some other units for energy are watts, calories, and there are several British thermal units for energy like kilowatt hour, which is used specifically for electricity. Now energy and work represent a force acting over a distance. I’m going to say that again, it represents a force acting over a distance.

When we think about work, we may think about just doing some type of physical activity or going to the place of work, well we have a physics definition for work and that means to move something over a certain distance. If I pushed on this wall and I pushed really hard, I’ve pushed all day, but the wall never move, I didn’t do any work by the physics definition. Now if I were to look at a big box on the ground and think I want to move it across this parking lot, so I just push and push on it and slide it across the ground, now I’m doing work because I’m moving that box.

You have to be doing something and so remember I said energy or the unit we use for energy, which is joule, is one newton over the distance of one meter. We notice here that distance is important because if I apply the force of one newton on the box for one meter, I did quite a bit of work. But if I apply one newton of force over the distance of two meters, I’m doing even more work, because I’m pushing it even further and so I used more work and so energy is the capacity to do work, it’s the ability to do work.

It’s just like if you get a good nights rest and you eat a lot of food, then you’re going to have more energy to be able to do work than if you haven’t eaten anything in a while and if you’re pretty sleep deprived. You have this more energy, you have more ability to do this work and so if I push the box with the force of one newton over a distance of two meters, I use more energy than if I push the box with a force of one newton for only a distance of one meter. You can see here the relationship between energy and work.

I’m going to draw a little bit of a box right here to talk about the relationship between energy and mass and so we have an equation, which is E equals M, a little o it’s a little O, C squared. E is obviously energy and then we have M, which is mass, but in this case, it also has a little O, which stands for the mass of the object.

Then finally we have C squared, which is the speed of light in a vacuum, the speed of light in a vacuum. That’s the way that you can relate energy to mass, so you’re looking at the mass of a particular object and then you use the speed of light in a vacuum which is a constant and you’re able to relate these two variables back and forth to each other. Again energy is the capacity to do work.

The next lesson: Heat, Energy, Work, and Thermal Energy, both lessons are included in Practice Tests.