Skateboarding without touching the ground...

[Andonyx]

Sorry, I know that title is probably reminiscent of something from Back to the Future II, but I'm afraid it's a little more mundane than all that...

Anyone have a better technical explanation of this:


The payoff: skateboarding for miles but never needing to set a foot on the pavement.
With arm motions dubbed "choppin' wood," "swimming" and "climbing," two Redmond natives have developed skateboarding techniques that manipulate hills and distance without ever needing to push off.......
And they ride for miles, keeping their feet on the board the whole way.

http://seattletimes.nwsource.com/html/localnews/134757050_skateboard17.html

It seems to me very much like the same principal that allows one to swing higher and higher on a swing, and even start swinging without using your feet to push off the ground. But perhaps someone has a more thorough understanding of this.

[garys_2k]

It sounds like it touches on reactionless propulsion, but I suspect the real explanation resides in more wheel friction with offset loads than on loads which are centered over the trucks. If you wave your arms forward when the friction is higher and back with it lower, you could induce a net board thrust forward. Note that the hill climbing explanation sounds like they may "walk" the boards mostly sideways up the hill, rather than letting the wheels roll.

[jj]

You guys are working too hard. You don't need differential friction or anything like that, just wheels that roll one direction and a steering mechanism (like is built into the skateboard).

You can push a skateboard forward without putting down a foot or grabbing a rail or anything just by pushing sideways back and forth with the right rhythm, working against the "trucks" that steer under the skateboard.

It's a dynamic manoever, it's work, and it wouldn't work if the wheels rolled in all directions.

I don't know quite how to explain it, but I can do the same thing with my feet together on roller skates (quads, not inlines), I've even seen people do this sort of thing with a bicycle, although I think the motions are a bit different. Basically, you're moving around your CM dynamically, and using the steering mechanism to work against the "no move" side of the wheel sometimes and the "roll" other times.

The "big wheel" things that came out a few years ago, wherein you waved yourself back and forth, and went forward, were similar, I believe.

[EvilYeti]

I don't see why this is news.

A friend of mine when I was a teenager (about 15 years ago) had a skateboard he set up with very loose trucks.

He could ride this in circles in his driveway for hours without ever touching his feet to the ground. He would put his weight way back and kind of swivel the back wheels very quickly. The front wheels would just bounce off the ground, all the traction was on the rear wheels.

In his case he was putting all his weight on one wheel, pivoting off it to throw the other wheel forward, then repeating. It would be like tieing your feet to a 2x4. You could still move by shifting your weight to one side and throwing the remainder of your mass forward to the opposite.