Last chapter we covered Newton's three laws, which can be used to predict how things move in time. You have to know what the forces are between objects, but assuming that, Newton's laws tell you everything. So what is there left for us physicists to do? Actually a hell of a lot, like surf, play bridge, sit around a talk about how smart Newton was. But seriously, buried in Newton's laws there are some important concepts that aren't at first too clear. Most importantly is the idea of conserved quantities. These have very important consequences to physics. The first one we'll talk about is conservation of energy. We'll define this thing called the energy in a while. And the neat thing about energy is that it is conserved, that is it doesn't change in time. You should understand that we don't postulate that it doesn't depend on time. We can actually derive it as a consequence of Newton's laws. That's one nice thing about physics. That you don't have to remember very much. A few basic equations is all you need and the rest can be derived. Of course you need quite an big CPU to be able to this in practice, so it's good to try to remember other things as well, like conservation of energy.
We'll start now by considering a thing related to energy called work.