 In this video I'm going to introduce the laws of conservation on one particular example, which is the law of conservation of energy. I'm going to start this video with a little demonstration and I want you to come up with an equation for my demonstration. What I have is a glass of water that is filled with less than half of water and I want you to find an equation that describes how much water is in the glass after pouring a bit more in. So this is the initial state. I have some water in my glass and then I'm going to add more and now I have the final amount of water in my glass. So please pause the video and think about how the initial amount of water in the glass relates to the final amount of water in the glass. Once you have written down your equation, come back to this video. So I think all of you have probably come up with something like this. A final amount of water is equal to the initial amount plus what I added. Now if I basically consider more general, I could say what I have after is what I had before plus the change. Now in my example with the water, the change could be positive or negative. The change could be I'm adding more water. So after more than I had before. The change could be negative. I'm taking out water. So what I have after is less than before or I could just keep one glass and then the amount of water in the glass is conserved. I don't have any change. What I have after is what I have before. Now this is the basic of the laws of all laws of conservation and there are many of them. You have conservation of matter, conservation of charge, conservation of spin, conservation of energy, conservation of momentum. So this goes on and on and on. And once you understand this one basic thing that what you have after is what you have before plus the change then you will understand all of these conservation laws. Now in the case of energy, so for energy, conservation of energy, of energy, I can rewrite this as my energy final is my energy initial plus the change. Now the change where we talk about energies can come in two ways. It could come through mechanical work or it could come through heat. Once again if my work is positive, my final energy will be higher than the initial one. If the work is negative, the final energy will be lower than the initial one. At the same time with the heat, if we're adding heat to a system, the final energy will be higher. If we're removing heat from an system, then the final energy will be lower. Now in your chemistry classes, you're mostly concerned about just looking at the heat. So you know this equation and form it out in mechanical work. In your thermodynamics classes, you're actually looking at both of them at the same time. And now in your mechanics class, we're most interested about the mechanical work and we're usually going to assume that heat is zero. Then there's even the simple case where we have conservation of energy where there's no external work entering or leaving the system where final energy is equal initial energy. So one equation for your chemistry class, for your thermodynamics class, for your mechanics class and for your simple mechanical situation for conservation of energy all based on the same principle what you have after is what you have before plus the change.