Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Mouse Trap Car

  1. Nov 13, 2004 #1
    Hi all, new guy from CT. We were just assigned a project in physics to build and design a mouse trap car powered solely by the potential energy of a standars mouse trap. The main focus is distance, and so that is what I am aiming for. I have my basic design laid out, as I will attach two eyeholes (the bronze kind that screw into the wood) to the front and back of the trap, and I will slide an axle through them connected to the wheels. It will be powered by a string that is attached to a hook on the axle, so when the mouse trap springs forward it puts tension on the string, thus moving the car forward. Here is my question. I am trying to figure out what to use as an axle/wheel. Considering I am going for distance, would the optimal setup be a small diameter axle, with a large diameter wheel? Or the other way around. Speed/acceleration really isn't an issue, however I need to consider that the mouse trap has a limited amount of force, so i need to have drivetrain components that have relatively low inertia. Sorry about the long post, but what setup should I use to roll the trap car a long way?

    Also, I am good with design/building, but I really have a limited amount of tools and such.

    For the wheels, I was considering stryrofoam plates or CD's wrappe with a rubber band. Axle I really have no idea. Thanks so much.
  2. jcsd
  3. Nov 13, 2004 #2
    Back when I did this project back when I was a freshman in HS so very long ago I believe we employed CD's for the back wheels with rubber bands around them. I can't say much besides it went so slowly that the teacher accidentally called the contest over before the car even went 10 feet. Over the course of 2 or 3 minutes it went a few hundred more feet. You're on the right track having an incredibly high gear ratio but make sure that axle's greased or it won't move.

    Your string attached to the axle (assumably wound around it at first) is about the best you can get with a mousetrap car. What formula are you being scored by? Like the formula when I did the project was mass of car * distance traveled / length^2 or something to that effect. Just remember that every piece of weight counts. I remember cutting holes in my cd wheels and wooden frame everywhere that wasn't absolutely necessary to get rid of all of the dead weight. Ah memories. Good luck!
  4. Nov 13, 2004 #3
    Thanks a lot Vsage.

    I'll have to check on the formula, so I'll report back.
    Do you think their is a much better way to mount the axles so that they have much less spinning resistance? Also, I was thinking that styrofoam plates considering they are lighter than CD's, that they would offer an even greater gear ratio, with less weight, wouldn't that translate into more distance/less effort? Or does the momentum of the CD's help at all?
  5. Nov 13, 2004 #4
    The key in what you just said is:
    You're dealing with potential energy here. So, you must ask yourself, "When my arm is in it's firing (spring loaded) position that is attached to the string that is attacted to the axel which will rotate my tires, where is all of the potential energy stored?"

    Try and figure this out. When you have, you will find an excellent way to increase that PE and make a great mousetrap car.

    Paden Roder
  6. Nov 14, 2004 #5
    I suppose the potential energy is stored in the spring itself. How would this benefit the car?

    Thanks, Matt
  7. Nov 15, 2004 #6
    Think about it a little harder. How are you going to get your car's rear wheels to move? The string will pull it, correct? Well, what's pulling the string? How far is it pulling it? Is there any way to increase that?

    Maybe this will shed light.

    Your thoughts...?
    Paden Roder
  8. Nov 15, 2004 #7
    I see..what I did was attach a 12" lever onto the spring itself, allowing for a greater distance of travel, and more revolutions. I tested the car and got something like 16m, which far surpasses the requirements. Thanks to all!
  9. Nov 16, 2004 #8
    Good job.
    Way to think it through yourself. After all, it is a learning process.

    Paden Roder
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook