how long can you keep running your body engine without puttg food in? so the conservation of energy, hey, biology right underneath it. here's a neat little device here. it's a generator. consists of magnets, these magnets, and inside here, i have a coil of wire. and i'm gonna turn that coil of wire, and the coil of wire is gonna turn inside the region called the magnetic field. and when it does that, it's gonna induce electricity. and when i do that, i can light the lamp. how that happens, we'll talk about later in the course. but for now, we can look at this in terms of energy. that light that you saw glowing, that's a form of energy. what was the source of that energy? it was the cornflakes i ate this morning. because it takes-- i have to work on this to turn it. see that? and if i wanna make it brighter, i gotta work more. isn't that neat? okay. later, we'll learn that if someone could keep turning this thing, we could generate electricity to light up cities. and sure enough, we do. and we have devices like this. and we put a waterfall over here and

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