Sunday, February 10, 2013

Python, Ramps, and Energy

We're early in energy in Honors Physics, and I went looking for an applet that I used last year with some animations of ramp races - you know, the flat one and the down-an-up one: which ball wins the race? which ball gets to the end at a higher speed?

Anyway, I couldn't really find it, but I did stumble upon the dissertation of Thomas Thaden, which was related to this sort of thing, and which has a big series of possible outcomes of the race. They're small Quicktime videos and I didn't think that they were big enough or clear enough for what I wanted to do, so I wrote a simulation in VPython.

I think that this is much more interesting than what I was planning to do, which was to just have them predict, argue, and then see the results (peer instruction-esque). Instead, I'll have them check out five different possibilities, poll them, have discussion, and see what kind of consensus comes. Maybe there won't be one, but we'll be defining the gravitational PE that day, based on our lab from the previous day (maybe more on that in another post, if I have time), so that could help.  I'm torn about whether to do that first or second, but maybe second is the way to go.

Anyway, the five models in the simulations for the down-and-up track are:

  • Correct physics
  • Constant speed
  • Constant x-dimension speed, constant y-dimension speed while on the ramps (tie)
  • Accelerate down the ramp and up the ramp, but back to ball 1's speed on both of the flats
  • Accelerate down the ramp and up the ramp (but too much, so that the balls end up tied)
The videos are here (not in that order :) - A B C D E 

Let me know if you're interested in the VPython script! Edit: Python script is available here. Let me know if you find it useful! There's a bug in there that causes odd behavior with some ramp configurations. Let me know if you find it!


  1. Very nice! I'd love to take a look at the script.

  2. As would I. I wonder if the kids could critique each script to 'find the error'.

  3. The first two videos on the page below present a very similar situation to what you describe. There are four ramps with different shapes but the same height, and a ball is released at the top of each one at the same time. They have a separate video that shows the ramps launching the balls off of a table. All of them land the same distance away from the table, which I think is a great way of proving that they have the same speed at the end of the ramps despite taking different amounts of time.

  4. @ Beyond: I love the idea of looking at the landing spot! Maybe I'll make one of these over spring break... @Brain and Theron - I'll see if I can come up with a halfway decent way to share that script