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Physics Projectile Motion Equations/Principles in jump building

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John18_6
Posts: 7313 - Karma: 49,160
After seeing some of the jumps build at prestigious parks (a51 and such) as well as some of the fricken massive booters in park shoots. It makes me wonder if they use physics equations to build them or if they just freehand them. For example, a perfect table should have the same landing angle as the takeoff. And the well built jumps have landings that increase in steepness to make landings have less impact. So on a huge booter that is a table, a skier who launches at 30° at 60mph will come back down at 60mph at 30° at the point where the landing begins, not including air resistance. Thoughts?
Oct 9 2013 1:34PM
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CKpolicy
Posts: 2587 - Karma: 2,463
a = b
a^2 = ab
a^2 - b^2 = ab - b^2
(a - b)(a + b) = b(a - b)
a + b = b
b + b = b
2b = b
2 = 1

Yay math!
Oct 9 2013 1:44PM
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Rparr
Posts: 5354 - Karma: 42,183
I bet more math goes into building those than simple projectile motion that is taught to highschoolers...
Oct 9 2013 3:09PM
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TheAtomicPunk
Posts: 111 - Karma: 14
lol yes.

"i took fizix in high skool i kan build jump nao"
Oct 9 2013 4:25PM
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corona
Posts: 12752 - Karma: 32,266
that works because you're dividing by zero to get from the 4th line to the 5th line.
Oct 9 2013 4:32PM
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p-fo
Posts: 9372 - Karma: 6,155
FIS actually has a published study on the design of Nordic jumps. I looked through it when I was doing my senior project on projectile motion on park jumps.
They went into much more detail, though, considering things such as the rotational mechanics of the transitions and air friction.
Oct 9 2013 4:58PM
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John18_6
Posts: 7313 - Karma: 49,160
Page 43 guys http://www.wpi.edu/Pubs/E-project/Available/E-project-043007-014523/unrestricted/TerrainParkIQP.pdf Sorry about non clickable link, on iPad.
Oct 9 2013 8:40PM
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Amarino
Posts: 218 - Karma: 2,417
Yes, saw a presentation on it in school all I remember is usually the landing is twice the length of the lip. A lot more goes into it but I forgot.
Oct 9 2013 9:02PM
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bobs
Posts: 4801 - Karma: 869
Well small world - Brown (the professor on that project) was the advisor for my under-grad capstone and masters thesis
Oct 9 2013 9:58PM
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HeathR
Posts: 4357 - Karma: 1,379
Not much math goes into it. It's based more on experience and feel. Things are starting to change though. There are so many different variables involved it's hard to determine how far someone is going to go . I have been Guinea Pigging jumps for ten season at the various parks I have worked in. I have always done it just by feel. Always worked good until this year when I broke my back testing a jump in New Zealand.
Oct 10 2013 1:05AM
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LuiKangJoe
Posts: 12 - Karma: 771
Which mountain?
Oct 10 2013 4:36AM
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CKpolicy
Posts: 2587 - Karma: 2,463
i didnt really even read it, just pasted it in. if i had made that myself, it would have been worse. im horrid at math.
Oct 10 2013 9:54AM
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HeathR
Posts: 4357 - Karma: 1,379
Cardrona
Oct 10 2013 9:56AM
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John18_6
Posts: 7313 - Karma: 49,160
You got balls man. Props. I am usually afraid to hit 20ft jumps without knowing the speed. I have know idea how you can hit 70ft jumps without knowing the exact speed. Personally, that's where I'd start using the equations. I think they should make an online calculator for these equations.
Oct 10 2013 9:58AM
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Loco-Deer-Slayer
Posts: 1400 - Karma: 675
It doesn't work like that just think about it, draw a picture.

Your landing speed is a function of the lip of the jump in relation to the landing height.  The difference in this height will make your landing speed faster than your take off speed neglecting air resistance(even including air resistance you should land faster).

Your x-vector velocity will be constant (neglecting air resistance) but your y-vector velocity will increase due to gravity.  Add the two vectors and you will have a greater magnitude of velocity than when you took off.

This is why step ups are so mellow.





Oct 10 2013 10:19AM
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John18_6
Posts: 7313 - Karma: 49,160
Shoot, when I was typing I forgot to mention that the jump is a true table. Sorry bout that. But seriously, step ups are the shit.
Oct 10 2013 10:24AM
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Bacon_n_Waffles
Posts: 106 - Karma: 48
No matter how you build it someone has to try it first...All that math can't help with that
Oct 10 2013 11:36AM
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John18_6
Posts: 7313 - Karma: 49,160
Yes, but hardcore math is nice to determine the speed needed in the transition of the jump. Then just bust out some radar guns, speed check, and if you are in the right speed interval, send it. That study showed that the transition speed for 46ft breck jump (and like 20 other variables) that a safe speed would be about 33.6 mph.
Oct 10 2013 11:55AM
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Bacon_n_Waffles
Posts: 106 - Karma: 48
One thing that you can't calculate on paper is the amount or lack of pop from the rider...also the location of the CG of the rider...the radius of the transition is also important
Oct 10 2013 12:12PM
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John18_6
Posts: 7313 - Karma: 49,160
They accounted for the pop in the jump equation but you're right, it's impossible to completely rely on it because pop is never going to be consistent. The radius of the transition was also accounted for, they measure angles every 2 feet of the jump to calculate speed lost in the the transition and ramp. This is the point where it seems easier to just go for it rather than try to calculate it.
Oct 10 2013 12:34PM
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WU-sconsin
Posts: 565 - Karma: 1,301
I agree with this you could use physics but it's really just unnecessary for it
Oct 10 2013 12:55PM
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TheButterHashira
Posts: 9691 - Karma: 1,702
What you're saying is true, but without the math there isn't a good way to objectively describe why the jump is good. Someone like Tanner Hall probably has a superb understanding of projectile motions and physics in relation to how he uses his body in the world, but he cannot articulate his understanding in a way that we can understand other than by being clutch as fuck on jumps and in transitions.

Snow park technologies uses physics to make their jumps and it works. Its a classic physics problem, but I am sure that they use computer modeling that can account more for the factors affecting drag such as number of X's in the tall tee size, temperature and structure(corn, cord, slush, ice) of the air/snow.
Oct 10 2013 1:43PM
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Dr.Dickless
Posts: 2620 - Karma: 1,392
actually 2=0 in your work, showing that your equation is undefined
Oct 10 2013 2:58PM
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I_liketobutter
Posts: 2664 - Karma: 997
This topic has already been discussed in another thread, but the guy above is on the right track. There are way too many dynamic variable that come into play such as pop.

Just breaking down pop:

-time of the pop?
-how much loading?
-how much extension?
-angle of pop?
-progressive or constant pop over the time period?
-any absorption? think about how delorme hits a jump

this is just pop, there are other variables and they all interact with each other. this is why skiing is so fucking cool, its all about feel and personal style/apporoach to something as simple as a jump. it is not a math equation.
Oct 10 2013 4:19PM
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Mr.Gaga
Posts: 2021 - Karma: 542
Everything is a math equaton.
Oct 10 2013 9:17PM
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theabortionator
Posts: 51263 - Karma: 157,459
I'm not saying that people don't use math, but a lot of it is done by feel.

Even people who ski park all the time, you see features and can instantly tell if they're set up nice or super sketch just by looking.
Oct 10 2013 9:27PM
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HeathR
Posts: 4357 - Karma: 1,379
I have worked with SPT during many jumps builds. They always have very detailed specs of how they want to build a jump. I would say that the jump ends up being built to those specs less then 50% of the time. There are so many things involved that what looks good on paper does not usually work out. That being said, I think it good to calculate everything, build to your specs and then adjust accordingly. I take a lot more scientific approach then I used to.


Oct 10 2013 11:05PM
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