Derby Day
This is a wooden derby car race, and it needs JavaScript to run.
You build your car on a workbench: you draw its shape on the
block and cut it out, sand it, paint it, name it, and choose
where its weights go and how its axles are tuned. Then
it lines up at the top of a four-lane aluminum track
against three of the neighbors' cars, and races four heats so
every car runs in every lane. The times are averaged, and the
fastest average wins.
What makes a derby car fast
The axles matter most. A nail straight from the kit has a burr
under its head and crimp marks along its shaft. Filing them off,
polishing through finer and finer sandpaper, and adding dry
graphite can save more than a tenth of a second.
Weight comes next. Air drag and the spinning wheels do not grow
with a car's mass, so a car at the full five ounces loses less
of its speed to them than a lighter one.
Where the weight sits matters too. A car with its weight about
three quarters of an inch in front of the rear axle keeps its
center of mass higher up the slope for longer, so it has further
to fall. Too far back and the front goes light, and the car
wobbles.
The shape matters least of the three a builder works hardest on,
though a slim wedge still beats a plain block.
Challenge a friend
Send your car to a friend in a link. They race their own car
against it, head to head, four heats with each car in every
lane, and the physics runs the same on every device, so your
car posts the same times on theirs. Nothing is uploaded: the
car travels in the link itself.
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