This is another experiment, where I was just experimenting with acceleration and different speeds for going up and down. This leads to smoother and more realistic movement in lots of situations. I also added a loop feature and a pen to track its movements (and make interesting looking things). Use the arrow keys to move the circle. If you touch the edge, the screen will loop. Press space to turn on the pen, then use W to increase the size, S to decrease the size, A and D to change the color, and E to erase. The acceleration feature makes you able to make curves with the pen and movement that you wouldn't be able to do otherwise.
NOTE: The loop feature makes the pen draw a line across the whole screen. This actually can look good in some cases, though.
