I am entered in a gravity racer competition which is for an AP Physics class.?

Question

My question is how will I make the gravity racer more aerodynamic. The things about the race is for around 1 meter, the car will go down an incline and for the rest of the race it will go on a flat surface. Any suggestions about what I can do with how I assemble the wheels or cutting the wood in a particular shape or even decreasing the affects of air resistance. The answer I use regardless of how I finish will receive ten points.

Answer 1

Use very narrow and small radius wheels on your car. the rotational inertia must be kept to absolute minimums so that most of the energy from the ramp will go into velocity of the car rather than into the rotation inertia of the wheels. this will provide the greatest speed down the track and assuming the track is short the you will get there quicker. If however the track is long you will want to do the opposite by making the wheels large to store the energy and when the car hits the flat section it will not be going as fast but it will go a lot further

E-mail me and i will be happy to explain various other little details but the main emphasis must be placed on the wheels and knowing the track length is very important to the design and outcome.

I will be able to tell you actual velocities expected at the bottom of the ramp and can calculate the expected distance the car will travel if i am given a little more information. in particular the size of the wheels, mass of the wheels, mass of the car and just so you know the aerodynamics are not going to be any issue at all because the relative velocities are well below speeds that need to consider design shape or aerodynamics. usually speeds in excess of 40mph are where dynamics become an issue and need to be considered.

Well travis is incorrect in the friction issue. You obviously want the wheels to spin freely but any extra emphasis on this will not gain any performance.The fact that all of the cars are going to be essentially the same with the coefficient of friction then the rubbing area makes absolutely no difference at all. This is because the friction is related to mg*(coefficient of friction) and area has no effect. I will also be happy to elaborate on this point a little more and explain a lot of fallacies friction,tires,roads, brakes and why contact area has essentially no effect.

Answer 2

Ok really what you have to do is to reduce the force of friction to make your car go faster. Aerodynamics on such a small scale are going to make only a fraction of a difference.
I would not worry at all about cutting the wood in any shape at all but if you want to make it aerodynamic go for it i guess.
The number one factor is going to be how you have the wheels connected to the car. What you gotta do is make the most frictionless thing possible for your axels(i'm guessing your wheels are going to be connected directly to the pins or whatever you use for the axels)
Try to make the axels as free spinning as possible by using good cuts and sanding the areas where the axels will be spinning. Try a variety of materiels to make the axels out of, and try to make sure there is as little contact between the axels and wood as possible.