Yo, i am no physisist and i need a formula

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  • #1
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Main Question or Discussion Point

i need a formula to figure out how much force i'll be putting on a skateboard when im landing. the area i'll be hitting will be roughly 9 square inches, i weigh 210 lbs, and i'll be falling from 10 ft and i just wanna know if my 9 ply deck will hold up,

deleted unnecessary crudness

Integral
 
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Answers and Replies

  • #2
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that deck has withstood alot. i was looking for a figure or a formula to let me know exactly how much force i am going to be putting on the deck. i can expand the impact point if need be, but it'll be a moot effort if the FIGURE i was ASKING FOR goes beyond the makers specs, which i have in front of me a
 
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  • #3
S_Happens
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It is dependant on a lot more variables than you have given, or will even be able to provide. It has more to do with human physiology (your landing is a very complex movement/distributions of force) than simple specifics such as mass.
 
  • #4
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It depends on where you are landing on your board as well. For example, if you are landing both feet exactly over the trucks then the wood is just going to be in compression perpendicular to the grain, whereas if you land with any of your feet in the middle the wood is going to be in a bending. Both these have different critical (failure) loads.
 
  • #5
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yo, is the board flat or on the side of a half pipe? makes a difference. canadian maple is the best.
 
  • #6
HallsofIvy
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We keep getting problems like this. Given weight and distance of fall, you can calculate the velocity and kinetic energy but the force that will be applied to stop the motion depends also on how long it takes to stop- and that depends on the softness and flexibility of the landing site.
 
  • #7
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alright. so say my feet are just over the trucks, im landing flat but in motion (moot point i believe) and i DO have a maple deck. any chance i could land it and still have a usable deck afterwards
 
  • #8
Integral
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  • #9
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well, seeing as a put all of those douches to shame, i wont worry.

no offense but i didn't come here to be insulted, but for help on a question that my feeble skater mind cant cope with.

step off your soapbox and help or go cure aids or something
 
  • #10
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amd by "my type" i am curious about what brainiacs like you think about those who choose to actually USE our bodies... and i figure your gonna say something about how athletic you are and simply i dont care. i know for a fact you wiouldn't have the testicular fortitude to try some of the stuff i've pulled off, let alone having the determination to folow through after 20 messy bails.
 
  • #11
Yo, the formula depends not only on your weight, but also your height, your waist size, chest size, and the length of your arms/legs above and below the knees/elbows, something about how 'smooth' of a skater you are e.g Rodney Mullen has smoothness = 1 and Daewon Song has smoothness = 10. Various assumptions go into the model about the motions you tend to make when landing, although the effect of these will mostly be determined by the smoothness parameter. A simple model would only depend on mass and smoothness of landing.

But you don't really need a formula, since you know that it is physically possible for skaters over 200 pounds to launch gaps way bigger than 9 ft. Check out this clip from Kanten Russel:


The bottom line is that it is up to you land without breaking your board. If we had a motion capture video of you doing the biggest gap you have ever done, then with a few hours of fun/work we could tell you whether or not you could land the jump, but in terms of whether it's physically possible: that has already been demonstrated by experiment.
 
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  • #12
Okay, after checking out some skating clips I think that a stiff landing takes about 0.05 seconds and a smooth landing takes 0.5 seconds, so a smooth landing would involve a peak force of 3000 newtons, while a stiff landing would involve a peak force of 30000 Newtons. Since your mass is approximately 100 kilograms, this corresponds to an acceleration from 30g (smooth) up to 300g (stiff). I suspect your board could survive the former but not the later.

Note: for the physicsts I doubled the average force to get the figures I quote. Remember that this is an order of magnitude calculation i.e. real physics done on the fly. Also I wish there was a forum in-between general physics and general discussion. This thread would be lost in gd, but is somewhat grotesque in gp.
 
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  • #13
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i appreciate your help. and, if successful i will send you a clip of me badassness. if not, i always delete my f ups so sorry if you wanrted a laugh. just calculate the most likely mess id make of myself and laugh at it. thx again and wish me luck
 
  • #14
Hey man you should be fine if you dont concentrate your landing in the center of the board. Try to have your feet positioned on the trucks and you will be good. Do post a clip. Id like to see what youre doing.
 

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