The Physics of the
Pinewood Derby Book

The Virtual Racing CD


Select Individual Items
Axle Polish Compound
Vary Car Parameter B

Min-max Value & nbr steps
Again suppose you want to look at friction effects on your racetime but over any range and not just relative to your current value of MU. So choose the [Min-max value & nbr steps] tab. Moreover, you would like to see what would happen if you were sitting at the finish line in Irving, TX, and watching Brett Bullet run 101 race heats. Well, the 4 heats that were run gave times of 4.045, 4.047, 4.029, and 4.025 seconds which average to 4.039 seconds. If you subtract each individual time from the average, square the result, add all these 4 squares, divide by 4-1=3, and take the square root of the quotient, you end up with something called the sample standard deviation. In this case it is 0.014 seconds and is a measure of how much "noise" or uncertainity is in the race, at least for a car like the Brett Bullet. So we apply this standard deviation to all 101 races while we increase the coefficient of friction slightly for each race. Notice that you still get the trend of increasing race times with MU, but you learn that any changes you observe in real life may not be exactly as shown by the straight lines and smooth curves that you get when you run a "Perfect Race" without noise. Nevertheless, the "Perfect Race" time represents the expected time, and over many races the times will average to this time.


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