Talk:How To Build a Pinewood Derby Car/Physics

This paragraph has a couple of problems:

"Now consider an 8.53 m (28 foot) track that consists of a 30“ ramp followed by a flat portion to the finish. The ramp section is 2.43 m (8 feet) long and the flat section is 6.1 m (20 feet) long. The travels the 2.43 m ramp at an average velocity of v / 2 = ..."

1) A 30" ramp? Ealier the article claims the ramp is four feet high. Which is it?

2) "The travels ...". What travels? The car, perhaps?

I would leave my id but some moronic entity deleted it, so you will have to make do with my IP.


 * Thank you 71.117.209.73 - 1) thirty degree ramp - hypotenuse is double the base, which makes life easier (8 feet of track for a four foot rise) and 2) car of course. --Kkmurray (talk) 03:03, 6 March 2008 (UTC)

Angular velocity?
Isn't it v = r omega, not omega = r v?

Tread pattern affects rolling resistance, but raising a wheel doesn't?
A "V" or "H" tread pattern reduces CRF because it "limits the contact area," but raising a wheel doesn't because the same weight is redistributed elsewhere? I don't know enough about rolling resistance to know which is correct, but if rolling resistance is independent of the contact area, then the "V" or "H" tread shouldn't affect it; conversely, if Crr does depend on the contact area, then raising a wheel will certainly reduce it.

Normal forces impact on friction
The normal force on the axle is not affected by the slope because the wheel always rides on the same contact area of the axle so there is no cos(theta) term in the equation.

Further, putting the weight off center (in the back) cause the normal force on the rear axles to be greater than that on the front axles, increasing the frictional force. So there is a trade-off between increased potential energy and frictional forces during the inclined ramp and the linear track. So the equation for the normal force N per axle is not just N/4. It must reflect the location of the center of mass.