Derby Talk

I'm still thinking about #2, Duane. It makes the assumption that the heights on each side will be the same, and while that sounds plausible, I'd like to understand more. I've got a feeling that the formula for this idealized car-track is like the formula for the pendulum ... the pendulum approximat...

I think that #1 is missing consideration of exit speed. With that adjustment, the KE losses to heat are different. I think that's circular reasoning. Which is okay on Pi Day! If you hypothesize that the KE diverted to nose-up rotations is mechanically recovered at the exit from the curved section, ...

If rules allow, I would try: extended wheelbase central com position rather than rearward, for equal weighting on wheels (try that both ways, if you can do trial runs or 2 cars) com as low as possible, to reduce tipping actions when wheels get jarred sideways mount front wheels so that the most-roun...

It requires energy to rotate a massive object, and the greater the mass moment of inertia, the more energy is required, for a given angular velocity. Therefore, via conservation of energy some translational speed must be lost due to this rotation. The question is whether the loss is significant eno...

To simply summarize (I think)... Some experimental evidence suggests that the mass distribution makes a difference in the elapsed time. Why it makes a difference is not obvious. In particular, the most experienced builders here and elsewhere in the PWD universe have found, by many builds and races,...

Hmmphffff.

I just told my wife that I wanted to get Doc Jobe's textbook as my birthday present.


hopeless, just hopeless.

Consider a heavy ballistic pendulum. If a shot is fired into it, then in a frictionless and airless environment it would swing forever. However, in theory the swinging could be stopped by firing a perfectly-timed, identical shot from the opposite direction. In both cases translational kinetic energ...

Before the curve and after the curve, there is zero rotation of the car nose and hence zero energy of rotational motion tied up in such rotations. Before the curve the nose is pointing downward (say, 30 degrees, or whatever the initial slope is). After the curve the nose is pointing level, so a per...

Doc Jobe effectively states this on p. 110 "...half the rotational energy is used to rotate the car to the 1/2-alpha position and the other half to decelerate the rotation from 1/2-alpha to alpha" [alpha being the angular difference in slope before and after transition]. So he's saying th...

It requires energy to rotate a massive object, and the greater the mass moment of inertia, the more energy is required, for a given angular velocity. Therefore, via conservation of energy some translational speed must be lost due to this rotation. The question is whether the loss is significant eno...

An ice skater spinning. When they move their arms out they slow down. Bring them in and they speed up. A car going through the transition is the place to think about the dumbell car being slower than the concentrated car. Yes; I had personal experience with the ice skater effect this last weekend, ...

The weight should be centered vertically (Vertical COM) at or below the axles. The effect is not small but large. In sketching out the geometry on a track with a 30-degree starting slope, it looks to me like lowering the vertical COM by half an inch will improve potential energy by the same amount ...

The weight should be centered vertically (Vertical COM) at or below the axles. The effect is not small but large. In sketching out the geometry on a track with a 30-degree starting slope, it looks to me like lowering the vertical COM by half an inch will improve potential energy by the same amount ...

I can't find the data right now, but I've seen science-fair projects that tested the effect of distributed mass vs concentrated mass. Concentrating the mass of the car does improve performance even when the net center of mass remains constant. Here it is: Cory Young's Results . Specifically, the &q...

I personally see no functional value in maximizing the ratio of tungsten weight to pinewood weight. The more experienced builders like to cluster all weight as close as possible to the com, but the physics advantage of that are (I think) quite marginal. At my lesser skill level, I think all that ma...