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Mousetrap Car Won't Move

  1. May 26, 2013 #1
    I have built a mousetrap car for physics however it will not start. It will only jump in place and then stops. A requirement for the project is that the car must be able to start with a marble is dropped on the trap meaning I am not able to remove ANYTHING from the trap. However when I set off the trap the car only jumps, as I have told you before. BUT when I pull back the snapper arm and set the string normal and DONT set the mousetrap, just letting the car go right afterwards, the car moves about 2 meters. This is a good thing but I NEED the car to be able to move when the trap is set off. Sorry if this is confusing but help please?
     
  2. jcsd
  3. May 26, 2013 #2

    Andrew Mason

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    Welcome to PF!.

    It sounds to me that you need a gear mechanism so that the trap spring closes more slowly. There is a lot of energy stored in that spring. If you let it out all at once, you cannot harness it to power the car.

    AM
     
  4. May 26, 2013 #3
    Thank you so much for replying. Do you have any suggestions on what kind of gear mechanisms I could use/create?
     
  5. May 26, 2013 #4

    vk6kro

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    I have seen a mousetrap car fitted with a long wooden arm attached to the mousetrap's moving arm.

    The string was attached to the end of this arm and the other end of the string was wrapped around one of the car axles.

    This gave power to the car slowly so that it accelerated steadily.

    The string has to detach from the axle when acceleration ceases so that the car can run freely. This was done with a small rod at right angles to the axle and attached to it. The string is looped loosely around this.
     
  6. May 27, 2013 #5

    Danger

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    While I agree with Andrew that gearing is the proper approach, I feel obliged to mention that coupling the trap arm to a flywheel might achieve the same result with fewer parts.
     
  7. May 27, 2013 #6

    Borek

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    Add a two pound weight on top of the car.
     
  8. May 27, 2013 #7

    Danger

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    May he borrow your wig for that?
     
  9. May 27, 2013 #8

    Borek

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    Won't work, too light.
     
  10. May 28, 2013 #9

    Danger

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    Is that with or without the batteries?
     
  11. May 28, 2013 #10

    vk6kro

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    The secret to getting good distance from a mousetrap car is to keep the total weight as low as possible.

    Using a light rod to extend the range of movement of the mousetrap arm allows many turns of string around the axle to be pulled off, accelerating the car as it goes.

    Flywheels and wigs add too much weight and gears are difficult to implement, so I'd go with the rod.
     
  12. May 28, 2013 #11

    Borek

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    I solved the problem as stated, OP never said anything about getting a good distance.
     
  13. May 28, 2013 #12

    vk6kro

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    Yes, you would have to know about that.

    In high schools, it is common to set oddball challenges like building bridges out of drinking straws or spaghetti.
    Or building the tallest tower out of drinking straws.
    Or building a cart powered by a mouse trap or a rubber band. Whose cart goes furthest, wins.
    It may just be for fun or it may count as marks like an exam, so it can get very serious.
     
  14. May 29, 2013 #13
    A long lever attached to the arm extends the time over which the force can accelerate the car. One can also use large diameter wheels and a pulley on the axle to further increase the application time. The jump is due to the downwards force of the snapper hitting the car upon closure. Most of the energy is transferred to the body when it slams into it. The wheels just spins to quickly for the car to move in this case.
     
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