Wednesday, October 31, 2007

Accelerating carts

I thought I'd start off my post with a descripting of a demo that I've just constructed.

A common textbook problem is the acceleration of two carts joined together with string to a mass hanging over a pull, and the tension in the connecting strings. Many students incorrectly assume the tension in the two strings is the same, which it isn't. It's pretty easy to show mathmatically that the tension differs, but it's always nice to be able to show physically that something is true. After a checking on the UMD demo room page and a couple other demo room sites I found that surprisingly, no one does this demo.

Here we use a system from Vernier, which has force sensors which can display their output on the computer screen, which is projected so the entire class can see it. To show the tensions, you want two sensors mounted on one cart since it's clearer that way that they're the same. Unfortunately, there's no standard mounting plate that allows you to do that. I ended up building a pair of 2"x5" plates with two 1/4" diameter posts sticking up from each one that the force sensors can clamp onto.