Just heard the Pinewood Derby question, and as a former three-time winner of "The Derby," I thought I'd chime in with my thoughts. Of course, in my youth, I just tried what worked, but now that I'm an educated folk, I actually have some explanations for those stragedies of old.
The first consideration is, naturally, aerodynamics. There were disputes in my day as to the best design, but I personally used the triangle. The back was around 135 degrees, and the front angle was small enough to meet the back with as long a base as possible given the dimensions of the block of wood. After roughing out, the top and side edges were all rounded, the front and back smoothed slightly and the whole car sanded down as smooth as a baby's bottom with the finest-grit sandpaper I could sneak out of my dad's supply. A base coat of color paint was laid down over the entire car, sanded smooth and covered with a thin layer of clearcoat.
The second vital step to winning a derby {and peaking at the age of
10} is the wheels. The wheels fresh from the box have a seam running
right down the middle. This must be carefully sanded off to give
proper performance. If this isn't done, it'll cause wobble, which is
the death of a derby racer. Also important is the installation of the
wheels. They must be put on absolutely straight. And finally, use
plenty of powdered graphite to lubricate the wheels.
The last factor, and the main subject of your caller, was the weight and weight distribution. The best way to add weight is with lead in a trough in the bottom of the car running from the front wheels all the way to the back wheels. Lead is a good choice for weight because it can be scaped away easily to fine-tune the weight of the car, even at the site of the event. Now for the science involved: the cars generally accelerate at the same rate down the ramped portion of the track, so they arrive at the flat with the same speed. A heavier car will have greater momentum, however, and the race is really momentum versus friction of the tires on the track. If all of the weight is localized over two of the wheels, the downward force exerted on the track by those two wheels will increase and the friction will increase, which will cause the car to slow down more rapidly.
Ah, the fond memories of those days of yore. If only I could still participate in those events. Of course, as a proud(?) owner of a 1980 Mercury Zephyr, I do often have to think about getting the most ride out of coasting down a hill. It's just a Pinewood Derby on a ton scale instead of a 5-oz. scale.
Keep up the good work guys,
Jeffrey Bodwin
