As a former Cub Scout who has many lovesome memories of build pinewood derby elevator car with my father , here are some view that may help .
Let ’s start with the basic fact that pinewood derby machine roll down a track under the influence ofgravity . cut the data track for a moment – lease ’s say I take two pinewood derby car and I cast them in a vacuum . We have all see ( or heard of ) the experiment where a feather and a heavy sword ball are drop in a vacuum . And we acknowledge that the feather and the clump fall at the same speeding . Therefore , if a pinewood derby backwash involved dropping two pinewood bowler cars in a vacuum , it would n’t count what the car looked like , how much they weighed or anything else – every race would be a tie !
Pinewood derby races are not held in a vacuum , however – they are held in line . We know that in air , a heavy brand ball falls much faster than a feather . So you want the car to be as heavy as potential . Here ’s why : The force act on the auto is calculated by the formulaForce = Mass x Acceleration . The speedup due to gravity is a constant . So the more mass , the great the force play acting on the car . This force is competing against the force exerted byaerodynamic drag , so you want as much mass as potential to increase the force . ( If you could somehow burn the exercising weight in half and in the summons cut the flowing pull by more than one-half , that would be a good intellect to not use the maximum weighting . On a pinewood derby car , it would be nearly out of the question to do that because things like the cycle and axles are producing most of the drag and there is no agency to eliminate them . )
As the railroad car roll down the track , there are threefrictional forcesthat slow it down :
Imagine that the tires were made of easy , sticky rubber – tyre stickiness would be a big source of rubbing . Since you have no ascendency over the tires , you’re able to ignore stickiness ( and other factor get to do with the tires like diam , rotational inactivity , etc . ) .
So let ’s look at the remaining two factors : melodic phrase resistance and axle clash . Your son ’s mind is interesting . rent ’s say that you could contrive acarso that it actually flew ; with the wheels just off the ground , axle friction would hang to zero . Any wing that bring forth lift also generates retarding force in the mental process ( seeHow Airplanes Workfor details ) . So the interrogation becomes , " Which is bad – the sleek retarding force of the backstage or the rubbing of the axle ? " The only path to determine the answer definitively would be through experiment , and these experiment would be baffling without very sensitive and specialized equipment . Or you would have to build a issue of cars and see how they perform compare to each other .
I am blend in to guess , however , that axle friction is miserable than sleek retarding force created by lift . Therefore , you would desire to create a car with the lowest sleek pull possible and work to drive axle friction to zero . One thing I do jazz is that the axles can generate a LOT of friction . What you desire to do is refine them ( chuck them up in a Mandrillus leucophaeus and polish with steel woollen , then rouge ) and then utilise a juiceless silicon and/or graphite lubricant to reduce friction . You also desire to make certain that the wheel are perfectly pear-shaped and balanced , with the axle hole dead essence in each wheel .
Hope that helps . Enjoy the race !
