The Physics of slalom skateboarding

[Elisa Campbell]

Hey Ya'll. Elisa here. My senior year is finally coming to an end, so I'm finally going to have time to get back on my slalom board soon. However, just before graduation my physics teacher has decided to throw a big project at us where we have to explain the physics of something in our lives. Naturally, I chose slalom skateboarding. I know a lot of you guys are knowledgeable in the physics of skateboarding and I was wondering if any of you had ideas on where to go with this project. Seeing that I usually have a pit crew including Bobby, Harms, Keith, Kenny, pretty much all you guys, I know pretty little about all the tech. stuff. Any help would be much appreciated. My e-mail is woody5o@aol.com. Thanks guys!

[Andy Bittner]

Hey, Elisa. Here's a thought, how about the physics of pumping? I'm not necessarily talking about the physical movement of the rider, but more about the way the board converts energetic input into forward movement.

To me, it seems as simple as this...

Without the resistance created between urethane wheels and pavement, the sideways energy of a strong turning thrust on a skateboard would simply cause the board to slide away to the side. However, the resistance created by the urethane's traction on the pavement contains the energy applied by the sideways turning thrust, causing that energy to redirect itself along the path of least resistance. The path of least resistance on a skateboard tends to be along the low friction, rolling path of the board, particularly in any direction in which there is already momentum. So, sideways energy runs into significant resistance and squirts forward instead.

I like this as a school project, because it explains something many people find completely mystifying, the ability to ride a non-motorized skateboard uphill, without picking up any wheels or putting your feet on the ground.

[Guest]

Maurus Strobel of the Indiana team would be the guy to talk to. I remember talking to him about his master's thesis in, if I remember right, the bio-mechanics and physics behind a skateboard pump....or some such thing.

Either someone here has an email address for him or you can get it via the "contact" function of indiana.ch.

[Tod Oles]

This has been keeping me awake for months...but I'm pretty stupid, so you all should have better luck, Tod

http://www.glenbrook.k12.il.us/gbssci/p ... u6l1b.html

[Pat Chewning]

Elisa,

If this is only a 1-week project then I suggest that you keep it simple. You might try something like this:

Assume a skateboarder enters a turn with radius R at velocity V (use reasonable values based on experience).

Assume that skateboarder pushes her mass a certain distance towards the center of the turn by extending her knees , arms, unbending at waist, etc. (Use your mass, use an estimate of the distance you can change your body position during a turn). (Simplify by assuming a point mass -- not a distributed mass, and a uniform displacement over time during the turn).

Develop the equations for the conservation of energy during the turn. (You are putting work into the turn by displacing an accellerating mass through a distance ). The work you put into displacing the mass during the turn should show up at the end as an increase in kinetic energy.

Play with various values and see if it makes sense. Draw some diagrams.

[Jadranko Radovanovic]

Elisa

Maurus will be the right person. He was at the sports university in Bern Switzerland and i think he made a project about the bio-mechanics and physics behind a skateboard pump.

here is his email: maurus@indiana.ch

Jadranko

[Jonathan Harms]

Elisa,
"Explain the physics of something in our lives" is a pretty wide-open assignment, as is slalom skateboarding as a topic. Does "explain" mean write a few paragraphs, or does it mean demonstrate using experiments, equations and/or formulas? I'm sure your teacher gave you some idea, but if I were in your position, I'd do my best to define the assignment as clearly as possible so you're not trying to cram too much in.

If you are allowed to pick a narrow topic, here's one suggestion: Try explaining why small wheels tend to work better for really tight slalom and tall wheels tend to work better for huge GS/Super G (to exaggerate/elaborate, think of why nobody rides 97mm Flywheels for TS, and explain why they wouldn't work as well as smaller wheels). I'm guessing it has something to do with acceleration of some sort, and/or the difference between keeping momentum going in one direction (think downhill or Super G) vs. redirecting it quickly and repeatedly (think really tight TS).

It's been years since my last physics class, so I can't help much with the actual explanation, but it sounds like you're at least partly looking for ideas of where to start. Hope this helps. Good luck!

[Elisa Campbell]

Thank you all so much for your posts an your e-mails. I can't tell you how amazing it is to be able to look to ya'll for physics help, I'm much more of a biology student. Anyway, thanks to all of your help I was able to narrow the field down to a specific topic and really did some fine research and put together some nice example equations for my paper and presentation. The final result was a long paper describing why we care so much about the "hardness" of our wheels. I did some research on the coefficient of friction for different ratings of urethane, and used them in equations to ficure out the force needed to overcome the friction between the urethane and the pavement. I even got to go into how that fancy instument the durometer woks. I'm sure it'll be a success thanks to all the help. Love ya'll and hope to see you all at some of the gatherings this summer.

[Gary Fluitt]

I'm sure that Michael Brooke would be interested in publishing your findings, as long as he can include a picture of you "researching" that durometer work.

[Carsten Pingel]

Hi Elisa,
I'm quiet sure that Dan Gesmer can also answer your questions concermimg "the pump".
He told me s.th. about it in Hannover while having breakfast ! .-)

[John Gilmour]

Let's see it- equations...what are those.....?

JG