My physics students completed their “Mousetrap Car Lab” this past week, and I caught a lot of the final part on video and created a montage for them to watch. Enjoy! (I’ll explain the lab below)
We are wrapping up our energy unit, and I had an idea for a challenge to my students: see if they can predict what angle a ramp should be so that their mousetrap cars would go up the ramp to the top, but not go over the ramp. The students placed markers at the top to see if they could “knock it over” before they rolled back down.
My personal experiences of physics from when I was in HS was that almost no lab worked out, but you could always fudge the numbers to either (a) claim it worked or (b) explain why it didn’t and still get an A on the lab. So I was a little worried this lab would be a complete flop. To my surprise, it actually worked!
The downside to this lab was that there were so many different parts to it, that I had to hand-hold many of the students through the math (mind you, I’ve got students who are in Geometry all the way to Calculus as seniors, so quite the range).
Here are the steps (as clearly as I am able to put them):
- Find the force of friction pushing back on the mousetrap car. They did this by not setting the trap and letting the mousetrap car roll down a ramp. They found the Gravitational Potential Energy and we assumed that friction was the only force doing work on the system. We also assumed that friction was constant as long as the mousetrap car was moving, no matter what angle ramp it was moving on (a decent assumption, in my inexperienced Physics teacher opinion).
- Find the Spring Potential Energy. Once they know the force of friction, the students released the mousetrap car on a flat surface (ideally with a surface as similar to the ramp as possible) and used the two formulas for work to find the Spring Potential Energy because it is the only initial energy (final energy is 0 Joules).
- Finally, they solve for what the Gravitational Potential Energy should be at the top of the ramp (before the car goes over) and use that height to find the angle at which the ramp should be set.
We spent a lot of time talking through the above steps, and I even had them complete a sample problem where I made up data for them to solve before starting the experiment. I could improve this lab next year by taking the time to type these into lab instructions and providing more explanations for the students to read as they get to the steps. Instead, I found myself going from group to group, re-drawing the same sketches and explaining the same thing over and over. Good thing the class is fairly small.
The only group that was unsuccessful was because their “tires” (aka CDs) did not have enough friction, and they made all of their calculations with the wheels spinning out at the beginning of their trials (I guess they didn’t think that would matter??). When it came time for them to go up a ramp, they did not have enough friction and the wheels just spun in place. All the other groups, however, had very different angles on their ramps and came very close on several trials. I was unable to videotape all the groups at once, and so I missed many of the successful trials. Next year perhaps they’ll be required to videotape themselves and e-mail me the video.
Overall, I really enjoyed the lesson and I think the students did, too. I was pleasantly surprised by how accurately the math came out, and will definitely be doing something like this next year!
PS–I made the video using OpenShot Video Editor, a free video editor for Linux, which is pretty sweet.
PPS–I have to thank Julie for her awesome video of the Barbee Bungie which inspired me to make the above video. That, combined with the fact that our school just made class spirit music-videos had me thinking that I should use the video for a fun music video.