Why I need a giant turntable.

My poor blog has been left alone too long. I apologize to my regular readers (all 2 of you!) but it has been the end of the first marking period and grades are due. My blog had to wait awhile. But I am back now and I have a lot to post about.

1. It was a great week for me professionally and it could not have come at a better time. My classroom has become a quagmire of unproductive modeling... but that is another point for later. I attended the DMAPT meeting on Wed at the Detroit Science Center. We had the facility to ourselves. I think the phrase 'kid in a candy store' needs to be replaced by 'physics teachers in a science center'. It was a blast. My favorite display down there is this giant turntable. It rotates and they provide various size disks to go on them. If you cradle them gently between your fingers and hold them upright against the turntable they will begin to spin and they will remain upright rolling along the turntable. We of course were experimenting trying to figure everything out about them. We noticed that if the disk leaned inwards it would move towards the center of the table. An outward lean would cause it to move outwards. If you turn it slightly to the motion the table is spinning it begins a wobbly oscillating path around the turntable that is fun to watch until the disk falls over. Great fun! But it got even better when one of the teachers pulled out a 1.5-2 inch diameter steel bearing. Now you might ask why he had that on him, and I would remind you that it was a bunch of physics teachers so really that should just be expected. Then you might add, "next you'll tell me that someone else had 216 bucky ball magnets in their pocket." And you'd be right again.
Anyhoo back to the ball. I had thought the disks were the pinnacle of coolness until I say the ball. At first we tried to repeat what we did with the disks with some success. It made a spine-tingling sound and traced small circles on the table. That was neat, but the best part came when we began rolling it across the turntable. When it went with the rotation it bowed outwards and came back and kept going. But the true magic happened when we rolled it 'against the grain.' The turntable was spinning counter-clockwise and as I rolled it onto the left part of the turntable the ball quickly moved in the direction of rotation and made a big arc around the right side of center. When it got to the other side and rolled back onto the stationary table it immediately returned to its original speed and direction of travel! It was so amazing to watch. Of course hypotheses abounded. We tried to capture it on video but the lighting was fairly dim. If it gets posted I will link it.

Okay. I'm tired now. The rest of this post will have to wait until tomorrow. Not quite as triumphant a return as I hoped I guess.