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Thread: Science Competition Help: Potential Energy Car

  1. #1 Science Competition Help: Potential Energy Car 
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    For a high school physics competition I need to build a cart that is powered by a 1kg hook weight that will be dropped from 1m above the ground. This is a distance competition. The course will be flat. There is no limit to the size of the cart but it needs to fit in a 6ft wide course. The organizers will give me the weight and I can attatch it anyway I want as long as it fits the above decription. Also, no vaults or ramps are allowed.
    Any help you can give me will be greatly appreciated.


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  3. #2  
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    make it light but rigid and reduce friction. CD's work great for wheels. Use good roller bearings for the wheel axles.
    You want to reduce weight to reduce friction losses, but you want to have sufficient weight to store kinetic energy and keep it on the ground.

    Whatever you do, make sure all wheels stay on the ground when the falling mass pulls it forward. You don't want it flying, because you'll loose a lot of energy on landing


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  4. #3  
    Forum Professor Wild Cobra's Avatar
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    Since it's a distance competition, you might use a multiplier. Maybe have your weight drop using a multi-gang block and tackle pulley, or drive a gear set that pulls a linger string. You can get like 6 times the distance on a pull, but at 1/6th minus friction, the pull. The more pulleys, the greater the distance. If your car is real lightweight, you might be able to use enough pulleys, gear ratios, or whatever else to get more than 20 meters from a 1 meter drop of the weight.
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  5. #4  
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    cd's? use old school vinyl records for the wheels. They can be picked up pretty cheap at goodwill. Balsa wood is a good investment. mounting the weight directly above your car may be a good idea too, and enough gear conversions that instead of going fast, you just go far.
    Wise men speak because they have something to say; Fools, because they have to say something.
    -Plato

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  6. #5  
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    what material is the course made of?
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  7. #6  
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    what a mess - Cement, it will be in the school's parking garage
    Wild Cobra - do you have any suggestions of what this pulley system would look like?
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  8. #7  
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    Is the dropping weight attached to the car, or pulling at the car externally?

    If it's the first, a simple spool would do. The smaller the diameter, the better. For example a diameter of 3 cm gives a circumference of about 9 cm or 11 revolutions. If your wheels are 30 cm in diameter, you'll drive 10 meter + inertia. If the spool has a diameter of only 1 cm (you'll need the wire to be as thin as possible), you'll drive 30 meter + inertia. (note: the larger the diameter of the spool, the higher your speed will be and the further you'll roll after the weight stopped dropping)

    beware that the support from which the weight drops might destabilise the car and flip it over (doing a wheelie). This problem will be higher with higher acceleration i.e. larger spool diameter. If this poses a problem, putting the weight more to the front of the car is better.

    On cement, you might have to add some grip to the wheels, like a thin rubber band.
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