The Physics of the
Pinewood Derby Book

The Virtual Racing CD


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Axle Polish Compound

Graphic 2-Car Race

Above is an example of the new Graphic Race Program where users can pick any two virtual cars from the [Race Group of Cars] program. When any pair is selected, the [Graphic 2-Car Race] tab appears, and takes the user to this screen. In this program, a lot of things happen, so go to Lecture 24 to see all the possibilities. In Lecture 24, there is given a case where MY_CAR 1.0_1.0_1.0 leaves square corners on his car body and sharp un-rounded edges on his wheels (still flat treads). So his wheel and body drag coefficients are both high at 1.0, but he moves the center of mass back a centimeter (CM = 1.0) to compensate. The car's name reflects these 3 changes. His competitor has the same car, but sands the edges and corners of his body and wheels to bring the air drag coefficients down about 10%. He is in a hurry so he leaves his center of mass at the car center (CM = 0), and names his car MY_CAR 0_.9_.9 to remind him of the parameter values.

So which car should win, and why? First, we assume the cars are made well enough that they track straight without excessive bumping. They are brought into the Paint Shop, colors are blended and applied, and the cars are raced on an inclined plane ramped track like the BestTrack. The graph shows that the lower air drag of the red car gives it an advantage on the ramp as its separation increases because of its lower air drag. But at the end of the ramp (EoR), Car B surges a small amount as its CM advantage kicks in. But it is not enough, as at the high speed of the coasting run the lower air drag becomes even more important, and red wins by a 0.075 car lengths about inch). Go to Lecture 24 to see the same race on a circular arc ramp like the Micro Wizard. And see what happens there. Now is this instructive, or what? Thus, the Graphic 2-Car Race is the icing on the cake for the Virtual Race.


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