Відео

This is good, but as a longtime skateboarder myself, I think this is missing the force of your feet actually pushing down against the ground or ramp when pumping. The harder and thus faster you push down on the board, the faster your pump will send you.

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

Cool control system, and probably works well for mobile so the user doesn't have to move their thumbs, and can maintain 'mental symmetry' of the joysticks.

Badass man

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?

p̳r̳o̳m̳o̳s̳m̳

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.

you ever posting pt 2?

​@UCTnd2Bf5OPMcOLmyZ8sgVaw Thanks for the tip. This was actually pretty interesting. Takes me back to my physics 101 courses. What a flashback :)

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?

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

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

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

Best break down I've seen.

The human body is a rechargeable spring.

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

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

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

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

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

Thanks for the explanation. Keep up the great work.

Thanks for a great tutorial!

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

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

Love this vid. Post more like this

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

Wow. Really enjoyed this. Well done.

give us a part 2!

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?

I've seen several sources that say that light at normal incidence to a birefringent material still has one of the polarizations changing angle, instead of having the light go straight through, and Snell's law doesn't hold for birefringent materials. There are also videos on youtube showing a laser at normal incidence to a birefringent crystal, and the direction of one of the polarizations actually changes when the crystal is rotated, while keeping the angle of incidence at 0. I also thought that birefringent materials just had two indices of refraction, where on depends on the orientation of the crystal (and makes an ellipsoid shape), but apparently Snell's law no longer holds at the interface for the extraordinary ray. I'm wondering if there's some more general version that does.

Thanks in 2018

At pi/2 wavelength from your starting point the intensity of light is 0,since both light waves at said given point have 0 intensity.Also to generate circularly polarized light don't we need a phase difference of pi/2?When you say shifting do you mean shifting the orthogonal wave?

omg you are so cool

Thank you very much for the video! It was very clear and helpful. I was slightly confused by one small point though, and I would appreciate it if you could clarify it: From 4:00 - 4:13: "But because we have different speeds of light travelling through the material based on the different polarisations, we're going to cause that shift like we saw before." So to be clear, the shift is the result of different polarisations having seemingly different indices of refraction. Here is where my misunderstanding lies: at around 4:39, you add a birefringent material in between two orthogonal polarisers. The light incident to the material will be polarised in one specific direction only. So how will the subsequent phase shift arise? (4:38 - 4:42, "but if we start adding the material back again, then we can start getting a phase shift..."). I thought that the shift only arises if you have two different polarisations that will travel at different speeds though the material resulting in the phase shift you described. What am I missing here?

4:15 I don't see the two polarizers...

thank you

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

very well explained thank you

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.

Hello, thank you for enriching the UA-cam community with your videos! To make sure no misinformation is spread, I wanted to bring up a seeming contradiction with other sources and get your input. In your example on normal incidence, I have understood you to mean that both the ordinary and extraordinary ray will propagate at angle 0. However, two sources I've been reviewing so far explain that the extraordinary beam in birefringent materials will not (except under specific conditions) propagate at a zero angle under normal incidence. What do? Seemingly conflicting sources: Wikipedia: en.wikipedia.org/wiki/Birefringence#Double_refraction "So even in the case of normal incidence, where the angle of refraction is zero (according to Snell's law, regardless of effective index of refraction), the energy of the extraordinary ray may be propagated at an angle." Another UA-cam Video: ua-cam.com/video/jevSOwBtqlI/v-deo.html#t=4m03s

This video is very fun to watch, makes me want to play with some kids in my family like that.

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

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

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

great video, thanks for the explanation

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

Thank you. I was being bombarded by textbook with information. Your video gave me a clearer picture 👍👍

Nice try - BUT pumping with knees is not the thing the Pros are doing at competition or in videos. They keep their knees in position on the flat. Your explanation does not - for instance - explain the principles in this video: ua-cam.com/video/BMDxbn5HDf8/v-deo.html which still is considered one of the best instructions! But maybe you may explain those techniques as well ? Would be nice!

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

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 :)