Cap'n Refsmmat

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I think you misinterpreted. Either it spins or it spins. Electrons always have [imath]\frac{1}{2} \hbar[/imath] spin angular momentum.

Rigidness in a road tire can be a disadvantage, since you don't grip an uneven road surface and you transmit every bump and jolt into the suspension. The Tweel will let you play with the tire characteristics much more than a rubber tire would, though.

http://en.wikipedia.org/wiki/Tweel

Yeah, softer rubber will give a larger contact patch but more rolling resistance, and will improve the ride smoothness at the cost of some handling characteristics. Tradeoffs all the way.

Friction isn't dependent on surface area. I think the answer, if there is one, has to be more complicated than this.

Traction is related to weight, yes, but a lighter car needs less traction, because it needs less force to stop. Why do narrower tires have less traction? Here's their paper: http://www.cs.utexas.edu/~pstone/Papers/bib2html/b2hd-AAMAS04.html Check out the diagram on page 7, where they have two six-lane roads intersection and traffic flowing in all directions simultaneously. There's been more research since then, with more fun diagrams: http://www.cs.utexas.edu/~pstone/Papers/bib2html/b2hd-JAIR08-dresner.html

Well, I don't think weight is quite so important for traction so much as weight distribution. A lighter car is easier to stop but gets less friction from the road. It's just the size of SUVs that kills its efficiency by making it so heavy. If everyone moved to Smart Cars and small sedans, fuel efficiency improvements would be much easier to realize. Of course, there are also tradeoffs of efficiency vs. emissions, where certain changes that make an engine more efficient also make it emit more pollutants. It's a difficult field.

The Earth isn't slingshotting all the satellites currently in orbit around it, since they started on Earth moving at the same speed as Earth. It's only when you have a spacecraft at a radically different velocity swinging by that you could affect the Earth's orbit any. Given how massive the Earth is, I doubt you'd have a significant impact on its orbit.

Yeah, the important part is that the planet doing the slingshotting is moving. So when the spacecraft whips around it, the planet "drags" it gravitationally. The planet loses a bit of energy when doing so.

It looked exactly like the insane pictures you see of free-for-all intersections in India, except all of the cars were moving at 40mph and somehow not colliding. If that can be pulled off in a large portion of cars, congestion will drop dramatically and rail would be less important. However, achieving the fuel-efficiency of rail is still difficult in cars, and cars can't match high-speed rail for long-distance travel. I think part of the fuel-efficiency problem is that as car manufacturers developed more efficient engines, consumers also demanded more powerful engines. Modern cars are just as fuel-efficient as they were years ago, but several times more powerful. If we cut back on the demand for high horsepower SUVs, fuel efficiency would be significantly improved. (Realistically, we should focus our effort on the cars getting 10-15mpg, not the cars that get 40mpg already. Going from 40mpg to 80mpg saves less fuel than going from 10mpg to 20.)

I've attended a lecture where a computer science professor demonstrated a simulation of his pet project -- automated computer-controlled traffic junctions. If your cars are computer-controlled, you don't need red lights, so long as the cars can communicate and negotiate an order for proceeding through the junction. This means there's cars executing left turns, right turns, and lane changes all through the intersection, weaving around other cars and dodging through the intersection, mostly without stopping. It'd do wonders for traffic, but you'd crap your pants every time you enter an intersection.

Upload it here: http://www.scienceforums.net/index.php?app=core&module=usercp&tab=members&area=avatar You uploaded it to the user photo place, not the avatar place.

Rail travel: It might take longer, but the seats are bigger and your junk won't be violated. Not a bad tradeoff.

Do you mean inter-city or intra-city? Because rail is exceedingly fuel-efficient for long-distance intercity travel, particularly with cargo: http://www.progressiverailroading.com/news/article.asp?id=16740 Intra-city commuter rail, for travel between suburbs and such, is also fuel-efficient and high-capacity if done right, compared to road travel.

I don't think you can get volunteer professional engineers and volunteer raw materials. Also, rail is the most efficient transit method, in terms of fuel costs and safety. It also has exceedingly high throughput if done well.

I'm doing a presentation on statistics and statistical abuse and it got me interested in learning more about statistics, specifically in the context of data analysis and scientific experiments. Does anyone have a recommended textbook or resource for learning?

It took us a bit of cleverness to get to this point. Equations are generated in large font sizes at high resolution, converted into a high-quality PNG by dvipng, and then resampled to a smaller size with antialiasing by mogrify. dave (one of our other admins) is responsible for most of it. [math]C(\omega) = \frac{1}{2 \pi} \int_{-\infty}^{\infty} f(t) \cos (\omega t) \, dt[/math] The PHP code for all of that is available: http://blogs.science...asing-ipblatex/

Looks like the current list is amsmath, amsfonts, amssymb, color, and slashed.

So how do you propose the rock moved, if no force acted on it?

No. You can feel the string pulling on your hand. That's a force. Suppose I tie a string to a large rock and pull on it, moving the rock. Is the string applying a force to the rock to make it move?

Well, there's your problem. They're mathematically equivalent. To stop it from flying off, it has to apply a force -- it's pulling on the weight to keep it moving in a circle. That's exactly what gravity does.

Er, yes it is. I'm not talking about its position, I'm talking about its motion. Suppose I look up at something orbiting the Earth. If it's orbiting, it's not moving up or down towards or away from me; it's moving sideways, from one side of the sky to the other. Gravity, on the other hand, is pulling straight down on it. That's perpendicular. Then why is the string taut? If you spin the weight really fast you can feel the string pulling on your hand.

They both apply forces perpendicular to the direction of travel. Why should they behave differently?

Question: When you don't understand how orbits can work, why do you insist on making your own theory, rather than learning what hundreds of other physicists have concluded before you? As I said, when you're in orbit, gravity is not slowing down. You can continue orbiting as long as you'd like.