My Newton Scooter

October 23rd, 2009

mousetrap_car1In Science class we’ve been learning about Newton’s laws. So, our teacher, Mrs. Stewart, gave us a project to do. The project is to make a Newton Scooter.

A Newton Scooter is a toy car that moves by obeying Newton’s third law of motion. It has to move 1.5 meters by itself. So, the Newton Scooter has to move on its own by one force acting on another force.

I looked on the internet for ideas. I found a Mousetrap Car that looked very cool. So, I decided to make it.

First, I got a rectangular block of wood and attached eye hooks on the bottom. Then, I put the axles on. After that, I put the wheels and washers on. I used the sliders that people put underneath furniture as wheels. Then, I glued the mousetrap on the block of wood. Finally, I coiled one end of a string to the axle and the other end I tied on the jaw of the mousetrap. My mom helped me a lot.

So, when the mousetrap is set off the jaw yanks the string and makes the string uncoil on the axle.

The only problem was that it only went about a foot! We decided it was too heavy. So, we removed all the washers and used a smaller piece of wood. We also found out that if the wheels are CDs it will go farther. So, we made the back two wheels CDs. We tried it and it went way farther! It went twice as long as it needed to go! I was so happy!

We then painted it pink and today I took it to school. Mrs. Stewart liked it a lot!

I’m so glad I got to do this project. It was sometimes very stressful, but I had a lot of fun!

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17 Responses to “My Newton Scooter”

  1. Harvey |

    Sounds like a fun project and the way you improved your original design was very creative. It’s cool you enjoy mechanical things — I was like that at your age.

  2. BK |

    I believe it must have been a fun and memorable experience. Instead of just telling you action reaction, I believe through a project like this, you will be able to understand and appreciate better Newton’s Third Law now.

  3. Brian Bagent |

    Amber, now compare the results you got with your scooter and take a look at the way the different sized sprockets on a 12 speed bicycle work with each other and see if you can come up with a theory about the mechanics of it.

  4. Tom |

    Amber, that’s a great project! Teaching theories can be kind of boring, but working with their practical applications is a much more effective way of learning. I also liked the way you figured out the original design flaws and then corrected them. Ever think about becoming an aeronautical engineer?

    Meanwhile, I’m still trying to work out that theory about the 12-speed bicycle that Brian suggested….

  5. Brian Bagent |

    The theory I want her to look at is why a larger diameter fly wheel works more efficiently on small diameter axle. The amount of energy she used to propel her scooter didn’t change, but the amount of energy that was transferred from the mouse-trap to the ground very obviously changed. The amount of potential energy stored in the spring on the trap is finite and independent of the size of the fly wheel or the axle. What the wheel and axle configuration do change is how much of the trap’s kinetic energy makes it to the ground.

    It works under the same principle as block and tackle does. With enough pulleys and rope, 1 man could pull a Hummer out of the mud by himself. Without the pulleys, it would take a team of draft horses to do the same job.

  6. Amber |

    Yeah, I had a lot of fun doing it. But I’m not giving up my dream to be a doctor!

  7. Tom |

    Well, doctors have to know about physics, too, particularly in some specialties.

    Brian, I would add that friction is an issue, too. From what Amber said, she used fairly fat, small wheels in the first design. Changing to CDs not only increased the diameter of the wheels but used wheels with a very thin edge, thereby decreasing friction (and the total area) in the contact between the wheels and the ground.

  8. Brian Bagent |

    The friction of the axle against the mounting brackets is a much bigger issue than the friction of the wheels against whatever surface they are rolling over, and neither are much of an issue in this case because the wheels and axle have relatively no mass compared to the amount of force being generated by the mouse trap. In this case, even the change in width of the wheels is of no moment because even though the old ones are considerably wider, there is still almost no contact (relative to the entire surface area of the wheel around it’s entire circumference) of the wheel with the ground.

    The mental image to be formed here is of the mouse trap acting as the large front sprocket of the bicycle to which the pedals are affixed. The axle is analogous to the small sprocket on the rear wheel of the bicycle. Now, the thing that changed with the two experiments was the size of the wheel to which the small sprocket was attached. This would be analogous to the difference between riding a bike with 14″ wheels as opposed to one with 20″ wheels. The 14″ wheel would have a circumference of about 44″, and the 20″ wheel would have a circumference of about 63″, so each revolution of the axle drives the bicycle an extra 19″ or so. Well, with the scooter, there is an even greater disparity between the circumference of the original wheel versus the circumference of the compact disc. That is why the updated version of the scooter went further – each revolution of the axle drove the scooter that much more.

    The mouse trap has a diameter of about 4″, so the total travel distance of the spring bar is about 6″ (if the spring bar could make a complete 360 deg. circle, it would be 12″, but it only travels 180 degrees). That means that on a very small axle, of the sort used here in this experiment, of perhaps 1/4″ diameter (meaning a circumference of about .75″), the mouse trap will force the axle through about 8 complete revolutions (6″ spring bar “circumference” divided by the circumference of the axle of .75″ = 8). If the axle is attached to wheels of 1″ diameter, the total distance traveled for the scooter will only be about 25 inches. Replace those 1″ wheels with 4″ wheels (about the diameter of a compact disc), then 8 revolutions of the axle will produce a travel distance of about 100″, plus whatever momentum has been developed, minus the loss due to wind resistance and the friction of the axle against the axle brackets.

  9. Tom |

    I’m getting a headache….

  10. Amber |

    Me, too!

  11. Brianna |

    I once had to make a car like that in high school for my AP physics class. We’d already taken the AP exam, so my teacher had us do “Physics Olympics”, which was basically a bunch of competitive team games in math, science and physics. Our car used CD wheels too, but it didn’t end up working very well. My hypothesis was that we had fastened them too loosely, which caused the wheels to wobble and made straight-line progress difficult.

  12. Amber |

    that’s cool. Thats cool that it was like races. that would be fun!

  13. Brianna |

    My AP physics teacher was one of the best teachers I’ve ever had, and I can say that after being in school more than twice as long as you have. I hope for your sake that you are so lucky as to have a teacher as competent and helpful as he was.

  14. Amber |

    I just found out today that i made a 100 on my Newton Scooter!!!!! 8)

  15. Brianna |

    Awesome 😀

  16. Tom |

    That’s great, Amber! You could probably get a job designing cars at Chrysler or GM — they need the help!

  17. Amber |

    Hahahaha! I don’t think that job is for me! 8)

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