MIT 3.60 Lec 14b Symmetry, Structure, Tensor Properties of Materials
PROFESSOR: Let the minutes of the proceeding show that I re-entered the room at 3:00 and 12 seconds, true to my word. OK, I wanted to give you one example of a screw axis that you're probably familiar with in everyday life. That was a telephone pole that I was very familiar with when I was a little kid because we used to love to wait until it got dark and our parents couldn't see us. And then, we'd climb up the thing. And wow, you could see all over the whole neighborhood. I'm surprised nobody said, what? They had electricity when you were a little kid? Yes, they did. But now it's all underground. So kids, I don't know what they do for recreation these days. OK, let me pursue this question of screw axes. We've seen what a 2 sub 1 screw access looks like. I just erased it. But it consists of objects of the same chirality extending left and right on either side of the principal axis. The symbol for a twofold axis is this. The symbol for a twofold...