Whelp, apparently working with linear friction welding gives you a serial killer face...

That was amazing. Slowed to the point where there was no chance of flipping, then veered off to the soft stuff off of the runway where chances of friction-caused sparks that could ignite fuel spills were much lower.

Dunno if this was fully planned out but the results were superb. That pilot either has astounding skill or astounding instincts - or maybe both.

I see shifters that engage / disengage wheels with various friction.

Certainly variable friction there. I've no idea if it would be in the range we'd need for something like this.

Sadly, it doesn't sound like something a home hobbyist could do much with...yet. Give 3D printers a few more years, and we might be able to try this out.

You know what would be less stupid, and (I think) quite a bit of fun? Variable friction wheels! I've no idea if there's a technology to do it, but imagine something like a throttle control that increased or decreased the friction as desired. Then you could track just as little as you needed to drift around that corner.

You also gotta consider that paper burns the surface with friction before breaking the surface of the skin. However I think the culprit is still location, location, location. I can get scrapes around all areas of my skin, but finger tips where most sensory nerves are clustered are generally cut by something blunt that I have pressed into hard enough.

If tracks were perfect, it should make no noticeable difference...until you fall over, then being stationary is obviously preferable.
BUT...tracks aren't perfect, so the train being bounced side to side WOULD make it easier to be pushed over.
Also, curves have a slight angle to them, so trains going a certain speed will remain flat in the curve...so going too fast or too slow puts you off balance. It's hard to tell if that piece of track is curved.
Wheels are designed so they are ALWAYS using static friction , even when moving. The portion of the wheel in contact with the ground is stationary. (except when skidding)

Upvote for his facebook name alone.
His show is OK...not great, not bad.
I'm surprised he doesn't make the body of his swords out of aluminum or magnesium, then use an exotic welding process (like friction stirring...
http://en.wikipedia.org/wiki/Friction_stir_welding)
to attach a stainless steel edge for strength. It would make them more wieldable with an interesting look.

Air is friction, same as the spinning surface. I think you mean air friction versus friction from the spinning surface.

Assuming so, consider that without a surface, that top could slow down until it was at rest, but with a surface, the moment it gets below a certain speed, it wobbles and hits the surface and the surface contributes significantly to the slowing down. To truly compare the friction of the surface with the friction of the air, you'd have to factor out the force of the surface stopping the top.

This means, either eliminating the possibility of the top falling in the zero-air method, or only measuring the time until the top falls below the wobble speed threshold. The latter seems easier.

It depends a huge amount on the shape of the top. The one in the original video has a lot of bits sticking out around in to catch the air and cause drag. The one in the space video doesn't, it's a smooth circular shape so its drag will be a lot less.

Drag and friction are just two forces acting on an object in motion. If they were equal forces surely the top would spin for twice as long if either one was removed? The fact that it spins for a lot, lot longer once drag is removed makes me think that in the case of that particular top the air resistance is a much higher force than the friction with the table.

That space video from @oohlalasassoon tends to proves you right -- there there is no friction on the pivot point, but the top is still surrounded by air. It isn't clear exactly how long it would take before the air resistance would stop the spin, but it seems like it would be quite a bit longer (orders? of magnitude) even than the top in a vacuum.

I wouldn't have called it that way; the pivot point is so small that it has an very small surface area. And the vacuum chamber would leave that variable close to constant, but still resulted in a lot longer spin time -- so the air resistance (friction with the air instead of friction with the pivot point) clearly does have an effect.

Interesting stuff!

Neat. Makes me wonder how long it would spin in the other extreme, surrounded by air but with zero friction. In my naive mind, I imagine it'd go considerably longer. And of course with zero air and zero friction it'd go on indefinitely.

Air resistance vs. friction. Who will win out?!

That happen because the slide is not all made from the same material. One strip has more friction, while the other is more slippery causing the kid to wobble, poor guy

From my experience, and physics class, that should only be true if your brakes suck. Physics don't lie, and I was taught that static friction is ALWAYS greater than kinetic friction...meaning rolling tires grip better than sliding tires every time. If your brakes are able to grip with more 'stopping' force than the sliding tire produces and still allow 'slip', they should be able to stop you faster than sliding.

Perhaps on ice that's true, or other slippery surfaces where the sensors get confused, or with really bad or broken ABS, but good ABS seriously reduces the distance to stop AND retains control by rapidly (thousands per second) pulsing the braking force up to maximum possible force without stopping the rotation. That should be more stopping force than locked tires can produce if the brakes are in good condition.

I've been in the car when an idiot friend decided to prove it to me, and slammed on his new BMW's brakes at about 70mph. The seatbelt hit so hard I had the wind knocked out of me, and we stopped ridiculously fast (WAY faster than when I've locked up non-abs cars on the freeway...repeatedly). Afterwards, he needed new brakes all around, because they gripped so hard and hot it warped the new rotors, but never locked up the tires...retaining static friction between the road and tire. Dumb...but informative.

Wouldn't that material be awesome for ships? less friction?