Moving Benches

Unfortunately, this week was not quite as Physics filled as last week was, without The Lion King and all. However, I did go to the Homecoming Game with the Marching Band where we were melting in the hot sun along with the rest of the fans, and I took the SAT where one of my extra pencils kept kept getting pushed off the side of my desk as my left elbow (I'm a leftie) brushed over it (Projectile Motion! Vyo=0, Vx, H=height of desk, X=distance from edge of desk/original position: -H=-4.9T^2, X=VxT). But that's not the example I'm about to discuss.

The moment of rotational Physics that I experienced this week (or the first good one that I thought of) was moving benches out on the soccer field during Marching Band on Wednesday. On Tuesday, Mr. Hotoke had thought of the idea that I could stand on a bench to conduct so that everyone could see me better, and so for that day and Wednesday, we had to move the benches about four feet from their original positions. As I started to move the bench on my own on Wednesday, I could only do it one end at a time because dragging didn't work, so I picked up one end and rotated it. Lifting the bench created an axis of rotation at the middle of the leg of the bench farthest from me. As I walked with the bench, my hands were applying a force perpendicular to the bench, as my body stayed in the same orientation (perpendicular) to the bench and I was moving parallel to my body. Therefore, since the force was perpendicular to r, the distance from the axis of rotation to my hands, the equation for the torque as a result of my hands is (tau)=rF. (Sorry, no values again. I was concentrating to hard on Band :-) ) This torque caused the bench's very quick angular acceleration from rest, later keeping it moving at near constant speed, then its deceleration as I set it back down. I then applied the same principles to the opposite side of the bench to place it parallel to its original position. Moving the bench back took the same motions, except in the opposite direction. Four examples of torque! Wow, and they only took about three seconds each. And the benches worked well; I could see everyone, probably everyone could see me as well as ever, and I didn't fall off, despite the fact that a light, movable bench on grass is not the most stable thing to stand on. A pretty good day. :-)