Thinking about circular motion is hard because we have to think in two dimensions. Those of us who were attached to positive and negative direction now need to think in terms of left, right, up, and down. It's harder than you'd think.
We played a new game today, a twist on the mistake game. I had groups of two put up two whiteboards, one with a mistake they thought was a good mistake. It turns about the best board discussions were around how to convince someone of their mistake. It also was great when students made two different mistakes on the two boards. I think next time, I'll ask the groups of two to make a mistake in at least one of the two boards.
We played with the Greek waiter's tray (see above), which is always fun. I make my students go through a three-stage training with the tray: first, a soft object that's grippy like a foam apple, then a roll of tape, which seems to slide off pretty easily if they're not careful, and finally, for stage three certification, a cup of water.
We had a little time today to start talking about what would happen if you launched an object horizontally faster and faster from a little ways off the surface of the Earth. I got to draw Newton's Mountain on the board, which is one of my favorite visuals.