My college students found 2 glitches in my programs.  The first was easy to fix.  There was an issue in the program Impulse Control where if you placed and then removed the impluse arrows that the change in momentum still persisted in the box.  

The second is a mystery.  In Water Drop Function Machines, there was an error where the goal number in the bowl was "undefined".  I couldn't reproduce it, so I put in a kludgy line of code to put in a replacement problem if that ever came up.  In that case the overall function is y=2x+3.

I'll have to keep an eye out.

While I was there, I fixed a small issue where the water drops wouldn't be visible in the last stage.