I the last issue of the Vernier Caliper they proposed a pretty good question
to their blog. They have a lab called Energy of a Tosses Ball. You put a
motion sensor on the table, hold a ball over it, throw is straight up, then
catch it. You get a PE and KE graph after you input the mass. When you have
the software add KE + PE to get total energy you should get a horizontal
line, and you do in many cases. When the person doing the lab used a beach
ball the line was curved (concave down). So, it showed total energy going
up, then down.
So, the blog question was why. There were the main possibilities people
wrote in.
1. Air Friction (seems right to me but no one gave a great explanation)
2. Buoyancy (Would be zero for a beach ball due to similar air pressure
inside the ball, so, not an issue)
3. Spinning (To get these results the ball would have to start out spinning,
slow down until max height, and then speed up its spin on the way down, so
that is out too)
So, I tried the lab. I was able to replicate these results. I guess its
air friction but I am not totally sure why.
The Caliper shows graphs of normal results and the weird ones.