Velocity is the rate of change of position in a traveling object. Scouts who want to know how fast their Pine Wood Derby cars are can do some simple math to find the velocity, or speed, of their cars. To find the answer, Scouts will need to know how long the Pine Wood Derby track is and the amount of time it took the car to reach the finish line. This is very easy for Packs who use electronic timers; other Scouts will need to use a stop watch and careful observation.
Measure the track from the start point to the finish line timer to find the distance cars will travel.
Race the Pine Wood Derby car using an electronic race timer or stop watch.
Calculate velocity (speed) by dividing the distance by the time. For instance: if the track is 32 feet long, and the car completed the race in 2.5 seconds, the formula is 32 feet / 2.5 second = 12.8 feet per second.
To convert your answer into miles per hour divide the feet per second by 1.4667 (1 Mile per Hour = 1.46666666666667 Feet per Second). For the Pinewood Derby car above, the math would be 12.8 seconds / 1.4667 = 8.72 MPH.
Convert to Scale MPH
Calculate the miles per hour a Pine Wood Derby car would go if it were full size by first finding the scale of the model. Divide the size of of the car "in real life" by the size of the Pine Wood Derby car. If your Pinewood Derby car doesn't have a real life equivalent, just estimate the size. Or judge scale by the size of the driver: if the car uses a Lego man driver the scale is 1/40th (assuming that a Lego man is about 6 feet tall). A car with an Army Man driver would be 1/35 for a 2 inch toy and 1/24 for a 3 inch toy (again, assuming your driver is about 6 feet tall).
Once you find the scale of your model, multiply the denominator of the scale (the bottom number of the fraction) by the MPH of the car. So, if your car is 1/40th scale, multiply the MPH by 40. A 1/40 scale Pine Wood Derby car that went 8.72MPH is going 348 SCALE miles per hour. Now that's fast!
If all that math makes your head hurt, use an online conversion calculator to help you out. See resources below.