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How would I calculate the deceleration of a vehicle (ATV), wheels locked, on dirt? How long would it take to halt? How fast is it decelerating?

I used this calculator, but it seems incorrect for a light vehicle.

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^I might add that our vehicle is under 700lbs, and a max speed of 35mph. Also, according to that calculator, no matter what the mass, a vehicle going 35mph will stop in about 62 feet (.7 COF)...does that mean a train will stop in 62 feet as well? –  Kevin Brown Mar 26 '12 at 20:24
    
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The calculator assumes a constant coefficient of friction which is probably a good approximation within a certain range of weights for rubber tires on a hard surface. For a train, metal on dirt would probably have a very different coefficient of friction, and also the weight of the train would likely deform the surface, so this analysis would not apply. Likewise, for a vehicle stopping wheels locked on a soft dirt surface, there will be a digging in effect which will be different than stopping on asphalt.

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Before we start fights over this again, perhaps it would be better to call it the coefficient of rolling friction? –  AlanSE Mar 27 '12 at 6:27
    
@AlanSE: The wheels are locked. –  Ron Maimon May 26 '12 at 3:26
    
I don't see why the coefficient of friction model should work for dirt. You need to measure, it might be strongly velocity dependent. –  Ron Maimon May 26 '12 at 3:28
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