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The physics of huge urban drops to flat?

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c-wayne
Posts: 253 - Karma: 906
this season i plan to drop some east coast cliffs (cliffs with no pow, and a flat, hard, barely snowcovered landing) and i was wondering uhh if i drop a 15 foot cliff with the speed a 10 foot banshee bungee gives you (not alot) to flat how hard will the landing feel? After watching cam rileys segment in network i wonder how people land on the flat to concrete from like 15+ foot drops? In some edits i notice people build small cheesewedges in there landings to land on to decrease the shock, does this work? How do people not like compress and break their legs by doing such huge drops?
Nov 18 2011 7:59PM
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sweatshirt
Posts: 1357 - Karma: 483
I don't know for sure, but I feel like the fact that you have skis and your energy can be defused by moving forward even slightly takes a lot of the strain on your landing.
Nov 18 2011 8:02PM
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ForeverYung
Posts: 8385 - Karma: 2,060
Ya I think the Energy fro
Nov 18 2011 8:05PM
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Z-Juice
Posts: 3151 - Karma: 1,504

I'm pretty sure that you need to have extremely strong quads to take an impact like that

Nov 18 2011 8:05PM
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ForeverYung
Posts: 8385 - Karma: 2,060
M moving forward decreases the pressure on you legs. /fuck moble
Nov 18 2011 8:06PM
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coldcuts69
Posts: 3718 - Karma: 1,888
.
Nov 18 2011 8:10PM
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firstdropkid
Posts: 149 - Karma: 63
i think it's fucking stupid to do it but go for it. i'm not impressed by huge drops to flat any more than i am huge drops to a nice tranny
Nov 18 2011 8:12PM
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spliff.Life
Posts: 7847 - Karma: 1,549
youve never studied physics im guessing
moving forward has nothing to do with vertical momentum
but landing slightly back ie bending your skis could take down the impact a little, but thats just no fun

Nov 18 2011 8:20PM
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JsNeagle
Posts: 1405 - Karma: 1,577
Just pre-tear both your ACLs, you should be fine.

On a less serious note, start doing squats.
Nov 18 2011 8:35PM
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fnly
Posts: 61 - Karma: 18
Speed does in fact help.  I was confused about this too, since a lot of physics does allow you to separate horizontal and vertical components of the momentum.  There are other things to consider in this case.

Imagine you are jumping into 1 foot of snow, and when you land, it can compress down to 6 inches.  This obviously absorbs some of your impact.  Lets say the impact itself is over 1 second (i.e. it takes 1 second to go from your max vertical velocity to 0 vertical velocity.)

If you are not moving forward during this jump, you are spending that 1 second of impact time on top of one small patch of snow, which can only compress 6 inches.  If you still have vertical momentum left over, it goes to your legs.  The snow under your feet has given all it can.

If you DO have a horizontal velocity during the drop, you are moving horizontally during the 1 second impact, spreading the force over a larger amount of snow.  The snow where you first touched down can give its 6 inches of absorption, and the snow right in front of that can give it's absorption as well.  You effectively use more snow to lessen the impact force.
Nov 18 2011 8:57PM
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Montana_Hoodrat
Posts: 1953 - Karma: 1,481
interesting.
Nov 18 2011 9:03PM
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dispatchQ_main
Posts: 2619 - Karma: 629
>implying you have studied physics beyond highschool and have a post secondary education.
Nov 18 2011 9:08PM
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84891jnf92048
Posts: 11552 - Karma: 2,550
dont do the fucking physics

just sack up and hit it, and if your legs explode, oh well, YMR.
Nov 18 2011 9:11PM
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belden...
Posts: 2914 - Karma: 1,274
Build a cheese wedge landing... of coarse it will help
Nov 18 2011 9:57PM
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tinkytwinky
Posts: 2451 - Karma: 1,571
By vertical momentum do you mean the force of gravity?

Lawlz

And moving forward disperses energy over a larger surface area, i understand that it makes no sense for skiing as you cant roll over and bounce up off of your skis like them parkour bros but that how they take those falls by dispersing their force.
Nov 18 2011 10:05PM
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californiagrown
Posts: 9794 - Karma: 2,014
hey wanna see me blow apart your theory as it pertains to this thread?




Dude is taking about urban drops and East coast cliffs. There is a 1/2 inch of powder over a foot of concrete/ice. that 1/2 inch will be blown out from under the skis on impact due to the displaced air alone.
Nov 18 2011 10:24PM
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tbayskier
Posts: 1138 - Karma: 1,642
uh no.  for any drop 15 feet and over there is going to be atleast 6 inches of snow noob
Nov 18 2011 10:32PM
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why
Posts: 2064 - Karma: 65
Click for larger imageClick for larger imageClick for larger image
Nov 18 2011 10:39PM
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zflink
Posts: 309 - Karma: 283
Change in momentum = Force * time

longer time of impact = less force applied to stop your momentum

so if there's snow piled to lengthen your landing it will decrease the force. Also the more angle the landing has the smaller the vertical component of the force will be
Nov 18 2011 10:42PM
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tbayskier
Posts: 1138 - Karma: 1,642
cam is fucking insane. but case in point, there are three big things going on here:

1. FORWARD MOMENTUM - lessens impact compared to going straight down.

2. NOT JUST "A HALF INCH OF SNOW"  (tho the landing is gnar and tiny as hell, it has some substance to it)

3.  STRENGTH -cam's strong legs and experience with this shit
Nov 18 2011 10:47PM
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james6345789
Posts: 4763 - Karma: 467
On a different note, Alex Bellemare's 50 foot fence gap rodeo 5 to flat landing was crazy
Nov 18 2011 10:52PM
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californiagrown
Posts: 9794 - Karma: 2,014
1) wrong

2) the amount of force that thin pile of slush will exert on the skis upon landing is minuscule, and will hardly make any difference whatsover in decreasing the impulse upon the rider. it is only there so the rider doesnt come to a dead stop and flip forward.

3) this is the answer.
Nov 18 2011 10:57PM
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tbayskier
Posts: 1138 - Karma: 1,642
really not wanting to start a shit storm here.  Can anyone back me up here? pretty sure I'm right on all of my points...

and for number 2 i do agree the snow helps to carry speed which boils down to point 1....which is apparently a "NO"
Nov 18 2011 11:00PM
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MikeWeinerONE
Posts: 501 - Karma: 1,215
pretend your sitting in a chair to land... keep your core strong, and bend your knees... you got it
Nov 18 2011 11:01PM
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californiagrown
Posts: 9794 - Karma: 2,014
F=m*a

the skiers mass is constant, and the skiers vertical acceleration is the exact same regardless of his horizontal acceleration.


how does horizontal velocity have anything to do with vertical acceleration?
Nov 18 2011 11:04PM
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tbayskier
Posts: 1138 - Karma: 1,642
have you ever hit a drop on skis before?  a flat landing is easier to ride out of if you have speed as compared to just poling of the edge. 
Nov 18 2011 11:06PM
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californiagrown
Posts: 9794 - Karma: 2,014
haha, and this has to do with your flight path matching the downhill landing better. if it was an uphill landing, it would make the drop more difficult. when the landing is exactly horizontal, it makes zero difference.
Nov 18 2011 11:09PM
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RubberSoul
Posts: 11249 - Karma: 14,642
right, so isnt the important part of the horizontal speed that it is changing the vector of your flight path in relation to the landing surface? and helps turn your vertical momentum into horizontal? comparable to the way a skateboarder has to take speed into huge gnar flat landings?
Nov 19 2011 12:15AM
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sweatshirt
Posts: 1357 - Karma: 483
so according to you, having skis is the same as just wearing boots? cuz im pretty sure you would break your ankles with just boots on haha
Nov 19 2011 12:20AM
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Brock.
Posts: 5698 - Karma: 1,332
"Flat" can be a deceitful term. Usually there is an abundance of unpacked snow on the landing which helps A LOT with impact absorption.
Nov 19 2011 12:24AM
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sk1color@do
Posts: 101 - Karma: 10
I remember the last time there was a thread like this. California is right, don't argue
Nov 19 2011 12:25AM
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RubberSoul
Posts: 11249 - Karma: 14,642
then can you explain to me skateboarders doing drops to flat please?
Nov 19 2011 12:31AM
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californiagrown
Posts: 9794 - Karma: 2,014
no. a bullet that is shot completely horizontal(ignoring the curvature of the earth) will fall to the ground at the exact same speed, as a bullet that is dropped. If anything, on a flat surface, the object traveleing with horizontal velocity will endure a more forceful impact because of not only the normal force from the ground, but also the frictional force that the the snow will now exert on the skis that were moving forward.

Nov 19 2011 12:33AM
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COskier
Posts: 1066 - Karma: 131
To the people talking about physics, you are correct that forward momentum would not change the impact on a block of some sort. However, as people have legs with muscles that do crazy things, it is possible to land such that you transfer some of the energy from the vertical component of the drop into horizontal acceleration, which is why people often land going faster than they took off. It is basically the same idea as pumping the transition in the pipe. Your initial speed matters because that way you can more easily overcome static friction in order to transfer said energy.

Other than that, landing on a slight decline helps because it lengthens the amount of time you have to decelerate and do the thing described above.
Nov 19 2011 12:35AM
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californiagrown
Posts: 9794 - Karma: 2,014
the reason is this: is it harder to satnd on a still board or one that is moving? the one that is still. why/ because when you correct your balance on a moving board, all that happens is a small change in direction, and youre back on balance. when still, there is nothing to push against to regain balance, so it is much harder to catch yourself.

its the same reason why snowboarders hop around all the time while standing, but look cool and calm while riding.

Nov 19 2011 12:39AM
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RubberSoul
Posts: 11249 - Karma: 14,642
i know the bullet thing... but i just dont understand how the vector you come in on in relation to the landing plane doesnt affect it... isnt that why we prefer to land on transitions that more closely match our flight path, to turn the vertical momentum into horizontal?

im not arguing per se, it's been like 6 years since my last physics course, im no expert here, but right now i dont see how what youre saying makes sense, e.g. the skateboard example
Nov 19 2011 12:39AM
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funkmaster
Posts: 617 - Karma: 1,876
horizontal velocity has nothing to do with the force upon impact if you are landing to flat... only would affect anything if you were landing on a surface angled downwards to your trajectory...
Nov 19 2011 12:41AM
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sk1color@do
Posts: 101 - Karma: 10
The y vector (vertical momentum) isn't ever turned into the x vector (horizontal momentum).
As far as pumping in the pipe, energy is always lost, and the skiers regain and gain speed because they put energy into the system, not because they are converting y speed to x speed.
Nov 19 2011 12:43AM
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californiagrown
Posts: 9794 - Karma: 2,014
The reactionary components of the vectors are always normal to the impacted surface and parallel. the vertical component of your vector will never change becuase you are a constant mass being acelerated at 9.82m/s^2 or 32.2ft/s^2 downwards. the reactionary vector wil have two components: 1 normal to the surface and one parallel. because the landing is flat, the normal vector is completely vertical and is the same as it would be if you have no horizontal velocity at all.


on a normal downhill landing, the vector will again be normal to the landing surface, but because the surface is ttilted forward, the perpendicular vector will now be much more horizontal.

think of it like a rotated axis. i wish is could show you with pen and paper.


im pretty sure my explanation is not translating.
Nov 19 2011 12:49AM
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COskier
Posts: 1066 - Karma: 131
Not really, by extending your body, you are extending your moment of inertia and putting more energy into the system. This is why if two skiers go at the wall at the same speed and trajectory but one pumps and the other doesn't, the skier who pumps goes higher.
Nov 19 2011 12:52AM
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sk1color@do
Posts: 101 - Karma: 10
I'd say it's pretty well stated.
Normal means perpendicular.
Nov 19 2011 12:53AM
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fnly
Posts: 61 - Karma: 18
skateboarders (and rollerbladers) need speed for a slightly different reason.  When they land, the wheels deform, flattening out.  If they have too little speed, this flat spot won't let the wheels roll correctly.  At higher speeds, the flattening is spread around the wheel.  More of the total wheel deforms, but no spot gets flat enough to trip you.

Nov 19 2011 12:53AM
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COskier
Posts: 1066 - Karma: 131
As I said above, this is only true if you have a solid type object such as can be modeled by an individual particle, this is not true for legs.
Nov 19 2011 12:54AM
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sk1color@do
Posts: 101 - Karma: 10
.....this is exactly what I said
Nov 19 2011 12:56AM
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COskier
Posts: 1066 - Karma: 131
Yes, but I'm saying that it is the same rotational energy in this instance, none is lost in the change from horizontal to vertical other than that taken by gravity and friction.
Nov 19 2011 12:58AM
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californiagrown
Posts: 9794 - Karma: 2,014
the legs would have to be able to push agaisnt something to transfer the vertical force into the horizontal( and vice versa). since the friction force between snow and basses on a flat surface is neglidgable, it doesnt happen.

When simon pumps the pipe, he is pumping the walls, becuase he can push perpendicular form the walls, which is actually horizontal to the flat bottom. there is a reason you dont see them pumping the flat bottom.

Nov 19 2011 1:07AM
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sk1color@do
Posts: 101 - Karma: 10
Exactly, just like I said.
Nov 19 2011 1:13AM
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_DUSTY_
Posts: 1097 - Karma: 686
Here's a drawing with vectors to help you guys visualize.

Click for larger image

If you are landing flat the ground will exert the same amount of force on you no matter what speed you are moving.The reason that landing on a slope helps is because the normal force is not parallel to the axis that the skier is landing on, this means some of the vertical force from the skier is converted to horizontal force. I can draw this out if you guys really need help.

There are three reasons you can land large drops on skis and not in shoes.

A. Skis spread out the area of impact, this means that your ankles will not shatter from all the impact. This is why you can't do 15+ foot drops in shoes.

B. Generally skiers land on slight downhills not complete flat, this means some of the vertical force is changed to horizontal force.

C. Finally the skiers legs are very strong, the legs can absorb the force by acting like springs. They spread out the impact time to the rest of the body meaning everything inside you is not slushing around. If a weak person hit a 15+ foot drop their legs wouldn't be able to handle the impact.

If you want to drop big drops work on your leg strength and make sure you have some sort of tranny.
Nov 19 2011 1:15AM
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_DUSTY_
Posts: 1097 - Karma: 686
And I have no idea how this got onto pipe while I was typing.
Nov 19 2011 1:17AM
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STAUSS
Posts: 8232 - Karma: 3,311
DUDE JUST SEND IT!
Nov 19 2011 1:18AM
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brosif
Posts: 654 - Karma: 28
No it doesn't because the normal force is going to occur right when you land. It's not like the snow is absorbing your impact for several seconds. It's really instantaneously. Unless you are landing in a bunch of powder, but I don't that is what we are talking about here. Besides, an inch of snow on cement is really not going to compress much...
Nov 19 2011 1:22AM
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