[ ]I'm walter lewin.I will be your lecturer this term. Make sure you have a handout, and make sure you read it. It tells you everything you want to know about the course. The course is about waves and vibrations, about oscillations,periodic, and not so periodic events. And, when you look around in the world you see them everywhere. For one thing:your heartbeat. That's a periodic oscillarion,at least. I hope that most of your it is periodic. Your breathing is some kind of a periodic motion. The blinking of your eyes, your daily routines, and your habits, your eating, your sleeping,taking a shower, your classes, and occaionally doing some work : all those are periodic actions. When you drink, I drink some orange juice. Notice as I tried to move the liquid down into my stomach that it's not a steady stream. But it's a periodic motion. Look at my throat. In fact,even if I don't want to swallow the liquid, but simbly have a bottle of liquid and I turn it over, and we all know that the water does't come out like a steady stream,but it goes glop. That's some kind of a periodic motion. I have a toy which I use to entertain my dinner guests. Particularly, physicists is interesting. And, this liquid here, the idea is to get the liquid there. And then, the problem is, how can you do it in the fasteat possible way? Well, if gou ture it over, you'll see the phenomenon I just mentioned which is the glop, glop. It's not a steady stream. It's almost pathetic the way that it runs from one side to the other. It will take minutes before it's there. But, it can be done and17 seconds. And, during the five minute intermission that we have, you may give that a try. And, I hope you won't break it, and see if any of you can rhink of a way that you can transfer the liquid in17 seconds. You have breakfast in the morning, and you casually put your breakfast plate on the table. What do you hear? Some kind of a periodic motion. And, two things can happen to this plate. It can move as a musilly, I call this as a musilly because I'm an astronomer. But, it can also wobble. In fact , something can wobble without moving as a musilly, and something and something can move as amusilly without wobbling. In this case, it does both. And, a fabulous example of that is what's called the Euler's disk, which is a metal disc, you'll see it shortly there, and this metal disk we are going to wobble in the similar way that I wobble plates. And then, we will follow its motion as a musilly, and the wobbling frequency. And, what is interesting, as you will see, that as [a musie?] motion, which has a certain period, that period gets longer and time , but the wobble motion, the frequency goes up. So, I'll start it here and then I'll show it to you in a way that is more appealing. And you can follow that. It's an amazing toy to work out to physics. It's very very difficult. I was told that Professor Wilczek at MIT once gave a one-hour lecture exclusively on the explannation of this Euler's disk. So,try to see this as a musile. motion. It will become clearer as it slows down furthear. You may be able to heae the wobble motion . I will hold my microphone close up.