How to maintain speed and momentum while spinning on a skateboard?

[cracker]

Hey I'm a skateboarder and been skaten for a while and I have recently been trying to spin as many times. So what do I have to do to keep my speed and momentome?

Also is there a rule for momentome that applies to everything?

By the way my I'm in Physics but my teacher is a crazy old black lady and all she does is give us homework and then the next class we spend a whole 90 minutes doing it and its only like 10 questions.

So does anybody know of any websites that tell you all of the propertive and equations and stuff that apply to Physics because I'm relly interested in who all this stuff works.

 

[Danger]

You're already on the best site that you can find for this kind of stuff. In this case, what you need is angular momentum. The best example is that of a figure skater going into a spin. With the arms spread, the rotation is fairly slow. Drawing the arms into the body increases the rate of spin in order to conserve angular momentum. The same thing applies to a star as it contracts to neutron star or black hole status. Although I don't know the specific mechanics of boarding (the only time that I tried to even stand up on one, I kept losing my balance), my suggestion would be to emulate the figure skater. Go into your spin in a crouched, wide stance. As you start to slow down, gradually straighten your body up and pull in your arms.

 

[rcgldr]

I was never able to spin around on a skateboard more than about 2 1/2 times, as I was losing a lot of energy spinning around in small circles, never really getting "centered" (my center of mass) over the rear wheels of the skateboard, which created drag from the cornering forces from turning in small circles. I knew where I needed to end up, but never figured out the body motion to get there. In spite of a few tries, I never figured out how to spin on one foot ice-skating either (again a "centering" issue).

The guys who can spin almost as well as a figure skater mangage to end up with an extremely small or zero effective radius while spinning on the skateboard. Some spin almost like standing still and just spinning with one rear wheel moving forwards and the other rear wheel moving backwards.

Crouching doesn't help. Starting with your arms outwards and pulling them in does. If you want to spin like one of the hot shot free style guys, you stand on just one foot, centering your weight over the rear wheels, and use the other leg just like a figure skater. This is difficult to do though, although roller skaters essentially do the same thing when they spin, standing on just one foot, and two wheels, although they are usually toe down instead of heel down.

Videos, (will update as I find them):

Conventional two foot style, only 6 360's (world record is 163 by Russ Howell, (an old timer like me but he kept at it while I quit while still in college, looking for a video.):

http://blip.tv/file/68792

This one is two footed, but much better, notice how little movement there is of the center of mass, occasionally there's some travel, but most of the time the rider remains "centered".

[MEDIA=youtube]WHmwutCWGAo[/MEDIA][/URL][/b]

 

[Danger]

Good post, Jeff. The reason that I suggest the crouch, and I might very well be mistaken, is that the knees and posterior are protruding as well as the arms, so there's more rotating mass to be brought to centre. Again, though, I know almost nothing of boarding.

 

[rcgldr]

Here's another video, but of a nose spin. You need quicktime 7.x to view this one:

http://sk8kings.com/new/video/RichyCarrasco360NoseSpin.htm