CAUTION: Although lead is not easily absorbed through the skin it is still a toxic material and handling precautions should be noted. Always wash your hands after use. Clean up afterwards and never use around food or place on surfaces where food is prepared. “And, keep your fingers out of your mouth”. That said…
Lets begin by clearing up what I’m sure is just a typo by some of my esteemed colleagues in the derby industry. Tungsten is not heavier than Lead and Lead is not heavier than Zinc. Even a pound of Feathers weigh the same as a pound of Lead. The difference is DENSITY and VOLUME. More accurately stated – The greater the density of a material, the less volume is required to obtain the same weight.
1 ounce of Tungsten displaces 1.47 cc (19.3 g/cc)
1 ounce of Lead displaces 2.50 cc (11.35 g/cc)
Now, lets get back to business..
Lead has about twice the density of the lead substitute (zinc) sold by others as weights for pinewood derby cars.
Even better…TUNGSTEN (W) has greater density than lead. This is not only a non-toxic alternative to lead, but it’s also 1.7 times more dense. That means you can cram more weight into a smaller area.
Using weighting material with greater density let you pack you mass into a smaller volume giving you more room for creativity in body styling and shaping. Concentrating your Center of Mass (CM) over a smaller area has definite advantages in how you distribute your weight to make the best use of your potential energy.
Check out my NEW WinDerby Lead Free Tungsten Putty.
The perfect way to make those last minute tweaks and CM adjustments.
OPTIMIZE YOUR CM – The farther back you can move the Center of Mass (CM), or balance point, the faster your car will go. Each 1cm (.394″) that you can move the CM from the center towards the rear will reduce your time by about .0014 seconds. To put this into perspective, this equates to approximately .6cm (.236″) at the finish line!. THAT’S HUGE IN A CLOSE RACE! But use this knowledge with caution. If your CM is too far back, your front end will wobble and bounce SERVERELY SLOWING YOUR CAR! Experiment and find the optimum CM for your car design.
Arm Yourself with Knowledge – The Physics of pinewood derby
Let’s keep all this weight stuff in perspective. Kinetic energy is 1/2 Mv2, so the car with more mass M must also have a slower velocity v for energy to stay constant. A fraction of a gram doesn’t make a huge difference at the finish line but one gram can easily mean the difference between winning and losing because of the high accuracy of race timing devices. If you do the math, 1 gram (0.03 oz) can still makes about 1/8″ difference at the finish line and some race timers measure 10 times closer than this. So, if you are really sloppy with your weight management and go in with a 4 oz car, you can be behind over ½ car length or 4″ at the finish line.
So, what is the actual importance of optimizing weight?
a) It is about the same importance as friction control (lubrication)
b) It is about the same importance as air drag control (streamlining)
c) The person inspecting your car (weighing) thinks it is a lot more important (like Aristotle-Lecture 1) and he is the judge.
d) Its a lot easier to get maximum weight, compared to optimizing a) or b).
Keep in mind – the weight of your car is just 1 more piece of a puzzle that has many interdependent pieces.