The physics of pumping a longboard 1

Here I describe the physics behind one method for accelerating yourself on a longboard without touching you feet to the ground a.k.a. pumping.

[@bostontricker211]

This is a better tutorial of how to pump than a video of a guy doing it.

[@user-bc9rl9wy7x]

You've just solved my questions of one year. You picked up the point!!! Thank you!

[@christopherwilliams2954]

This video helped me soooo much with my long distance pumping technique. Thank you for breaking it down so well. I cannot begin to tell you how frustrating it was to watch all those “how to pump” videos that inadequately explain actually how to pump...thanks a bunch

[@JediMasterPhilip]

Thank you. I was wondering what would happen if you scienced at longboarding.

[@davidmorel9453]

Woah, thanks, that is exactly what I have been wondering for a while, but I'm not good enough at physics to dig further and find it by myself. Thanks for the explanation, I'll share it around :)

[@gradies]

David Morel Thanks. Glad you liked it.

[@joeclark5341]

This is awesome. Thank you for taking the time to create and explain these concepts. Hats off. 🤙🏼🤙🏼

[@steven.y5982]

a great video! It really solved my doubt and applied to reality pumping 👍 Can't wait to see the episode 2

[@treyjones775]

Wow. Really enjoyed this. Well done.

[@jean-baptiste6479]

The human body is a rechargeable spring.

[@zombiejehuty]

Thanks for the explanation. Keep up the great work.

[@jasond1881]

Best break down I've seen.

[@noahb7947]

Love this vid. Post more like this

[@NurseZuniga]

Thanks for a great tutorial!

[@alexandreruelland5313]

Perfect, now i understand ^^ thanks ! (i love ur little skater btw, really... realistic :p)

[@johnwilliams-dg6qx]

great video, thanks for the explanation

[@Hotwire_RCTrix]

Fantastic ! I honestly thought this was a myth until I saw your explanation.👍

[@mharouny1]

FINALLY!!! It was bugging the fuck out of me!

[@cjcar178]

I like that analogy of converting linear momentum to angular momentum and then back to linear momentum just by weight shift and essentially changing your rotational inertia however if you think about locomotion by tick tacking (on a regular skateboard) there is something to using the friction from the wheels to propel you sideways. Without this friction from the wheels you wouldn't be able to take advantage of pumping and your wheels would just completely slide out.

[@franciscoggyy]

very well explained thank you

[@hiekevanrijswijk8222]

Smack into the molecules, never saw it that way. Hilarious, great

[@flylaw5613]

Yes....yes...Thank you!!

[@neuvation6607]

Gyration, nice video... also please do one on sliding/drifting

[@owensvalleycomputerrepair2834]

Badass man

[@IvoFigueira]

Very nice video! Have you made a second video about arms and torso?

[@gradies]

I want to. I was talking with someone recently about this. Thank you for giving me some motivation to do so!

[@normanfreund]

Thanks Garrette, makes perfect sense. I am a mechanical engineer, so I guess it makes sense for me. I have seen so many videos on pumping, tried them all out and never really helped. Now that I understand the science behind it, I should be able to progress better. Will give it a go today. Same principle for ice skaters doing spins, close in your arms and you spin faster. Great video, ever thought of being a lecturer at university?

[@gradies]

Thank you very much. University professor used to be a dream of mine. Now days I get my lecturer fix by teaching my coworkers things they don't care about.

[@karanoidji]

@@gradies I never got my hands on formulae to explain pumping, but there seems to be some more forces and acceleration methods to consider. E.g. your mass center should travel a trajectory that is closer to a line (maybe even straight line), and then you can twist your body around center of mass thus propelling your feet with a longboard further down the circle you're currently on. Still, your explanation helped me to draw some more intuition about how to pump efficiently and make a connection to how one would propel themselves on a swing.

[@gradies]

@@karanoidji you are absolutely right, which is why I labeled this video with a "1." I intended to make more explaing the physics of each method, but I never found the time.

[@mykytakostiuk4196]

thank you

[@papa28100]

Do you mind explaining the physics for sliding? Like what is it essentially?

[@schaventalakimungous4855]

you ever posting pt 2?

[@morphykg1503]

Is this the same kind of physics involved when you slingshot a spacecraft around a planet's orbit so that it can gain speed to the final destination?

[@na_schaeller4348]

Ah...I don`t like physics, but this seems to be true :D Nice idea BTW

[@mateuszkubala1800]

Can you make more, for example what you mentioned at the end, with using your arms? Please, you're great at explaining.

[@gradies]

+Mateusz Kubala I'm glad to hear you like it. I put this up as a Khan Academy contest submission, but its great that people are enjoying it. Now that you've asked I will have to make more. :)

[@mateuszkubala1800]

Thank you, I can't wait. By the way, are you a university student? I'm starting a BSc Physics degree in September and I'm looking forward to it.

[@gradies]

+Mateusz Kubala My bachelors is in physics and my PhD is in Biomaterials. My physics degree was finished 10 years ago, but I use the tools for everything all the time. Have fun, its a powerful toolkit.

[@edelhardtearnhardt8171]

Do you happen to know why it is possible to "inch forward" on a skateboard, from standing still, feet on the board, just by sort of pushing your feet forward? About the flat ground pumping, would you accelerate if you didn't bend and straighten your knees? My experience says yes, but I think based on your explanation you should net 0 velocity gained as you lean into the curve and back out of it.

[@gradies]

When you move the board forward, you do it fast by moving your body backward a bit. Then you reset you body position forward, but the static wheel friction prevents the board from moving if you do it slowly. If you had frictionless bearings this wouldn't work. Just leaning into a turn produces a component that aligns toward your center of curvature, so it is very possible for leaning alone to contribute to your acceleration. However, extending your legs allows you to start the turn with a higher rotational inertia and then decrease it while at speed. So it magnifies the effect.

[@tkfritz5790]

I've always been terrible at math but this makes a lot of sense and is actually pretty cool! Thank you!

[@lucastrever]

Thanks for the explanation :) I do still have a question though - How does the process of accelerating via this pumping technique conserve momentum? When not taking friction against the ground into account, how would the skateboarder be allowed to increase his momentum over the course several turns? Or, in a more concrete way: You mentioned that one has to expand when leaning into the curves, but wouldn't the neccessary compression in between the expansions cancel out the gain in momentum by increasing the moment of inertia each time?

[@gradies]

Great question. You are spot on that momentum is not conserved without taking friction against the ground into account. Therefor, all momentum gains comes from the earth through lateral wheel friction. You are changing your moment and rotation axis. When you compress, the axis is infinitely far away, and the compression is in an orthogonal direction, so it doesn't change the moment. So the compression does nothing to your momentum, but get you into position for the next expansion. During expansion you are pushing laterally against the wheels, doing work against the centrifugal force in your reference frame, while friction is providing the centripetal force, so the momentum you can pull from the earth is limited by static friction (wheel durometer etc.).

[@nevaknowmanamesame5089]

omg you are so cool

[@fuckmyego]

give us a part 2!

[@1KeyJee]

Thanks in 2018

[@snutteplays5200]

Wow wow wow wow... Thats alot of nonunderstandable stuff for me. When youre going uphill the ramp have your knees bent and as soon as you roll up straighten your knees. I know how to pump but this was was overcomplicated wich was literally unnecessary but i guess this video is for old physics teacher who likes skateboarding.;D

[@gradies]

If you want me to explain anything I can try to help, but the intent was to provide a physical explanation for how pumping can create forward movement, not to give a pumping tutorial.

[@snutteplays5200]

Well if you wanted to do that you could simplify it a hundred times. A simple tutorial and why you get extra speed was made by "never stop improving". A youtuber...

[@gradies]

@@snutteplays5200 The first two words of the video are "the physics. . ." If you dont want physics in your physics video I can't help you. I wasn't trying to compete with what is out there. I was trying to fill a void. When I was learning this I would have liked an explanation of the physics. Once I figured it out, I shared it, and I kept the physics to a high school level. Again, if you want help in understanding, I can help, but I'm struggling to find value in your criticism. Is there a specific part that you found superfluous? Otherwise it just seems like you are not the intended audience, which should have been apparent from the title of the video.

[@snutteplays5200]

@@gradies im from sweden and im not from england or us. I still learn english in school but i just think that you made it more complicated than it really is. And i dont know if you intended to do that but doing that would just be stupid since the easier you make it you probably understand it easier... over complicating physics is just unnecessary.

[@snutteplays5200]

@@gradies And maybe you can simplify it a little bit to make it easier to understand for me. All those drawings confused me...