Is there a sticky about why we say that golf ball dimples would not work on cars? I know that this was explained many times before I joined the site and many times since. It seems like we usually tell them to use the search function and then someone explains it anyway.
So, please excuse me for bringing it up.
Jserman28 mentioned it and I found a picture of the Mythbuster car.
And this:
Mythbusters golf ball car, Hot Wheels style | Redline Derby Racing
He took two identical Matchbox cars, weighed them, ran them ten times down his track, drilled 126 holes into the one that lost six races, weighed it again, added enough clay to the bottom to bring the weight back to where it was, and then raced them again.
The car with dimples, which had been slower, won 8/10 races.
I would not say this was "scientific," I imagine there were many problems. I wish that he had gotten the whole thing on video. Then he could have gotten times and could have said how much faster it was and we would have more reason to believe him.
I did a little searching regarding pinewood derby cars and found this:
Derby Talk - View topic - How come no one puts aerodynamic "fenders" on cars?
Some guy stating that the Reynold's Number for a pinewood derby car indicated dimples would not do anything.
And this:
He said that it went slower than he expected.
Someone said that pinewood derby cars went 8 MPH, someone else stated twelve, and a third person wrote thirteen, but everybody believed that the speed was far too low for aerodynamics to matter.
Except this guy:
Pinewood Derby Stories and Photos from Maximum Velocity: 2/20/11 - 2/27/11
He tried a technique discussed in a booklet that he read. Those pins are supposed to be turbulators. He did A-B testing with ten runs each:
Quote:
With the turbulators, the car ran a 2.503 average time with a standard deviation of .003. Without the turbulators, the car ran 2.504 with a
standard deviation of .002. The one thousandth second difference is
less than the standard deviation, so it is not significant. The test
was re-ran with a similar result.
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I have thought about Pinewood Derby since joining these forums and thought that we had a better idea of how to aerodynamically shape a car than most people, but then I remember that the fastest cars usually had the smallest frontal area.
Would dimples make an aerodynamic shape worse?
If I ever get to talk to my nephew again, I might mention this as a possible science project for his school. Mythbusters busted by ten-year-old boy!