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instant death at those speeds dont even need an equatio to know that
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Of course. But that's not the point. That's why I'm curious what it would be comparable to.
Like say, being hit by that guy is like being hit by a truck going 80? Because I know for sure that the breaking distance is proportionate to the square of the traveling speed, so I think that so is the force of the projectile. That's why bullets do so much damage even though they're super light, no? 
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I'm upset right now :<
Got to watch a cool vid, though!
Edit: To actually answer your question.
You're thinking of forces, so just do a simple F = ma
the acceleration in this case the body's negative acceleration imparted onto it by the object he is impacting. Let's say he slows from your 55 m/s to 0 m/s over the course of .1s
F = 75kg * 55 m/s^2
= 41250N
The reason I was upset: bullets don't usually kill b/c of their force impacted. They kill because of the shit they tear up. A bullet imparting minimal amounts of it's energy on the human body but passing entirely through can easily be deadly b/c of the systems it damages.
Double Edit: For all the cool kids fresh out of ES201. I'm well aware that this is a horrible approximation for the body hitting an object at 200km/h, but it shows an easy approximation of the force with which a body moving at that speed with that mass will impact. In the real world the body isn't just a 75kg unit, it's a system of attached masses. Upon impact the body would hinge around various points (and additional points of impact) and decelerate in a much different fashion. End result: Still dead, still hitting real hard.
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United Kingdom16710 Posts
I'm not really sure what you're asking for. Comparison between him colliding with a tree and a person? If so, are you looking for specific measurements like impact force, velocity, kinect energy...etc? or are you more interested in how the material, surface area, density, shape...etc of the second body would effect the outcome of the collision?
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he's going 200km/h. That's about 5.5m/s.
It's 55 m/s.
A fall at terminal velocity results in death. Gliding near this speed will have the same result if you crash against a tree or something.
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Well I don't know the answer but wow, I want to do that.
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can tell you this, apparently a freaking coachroach-llookin flying bug can kill a human when we ride a bike at like 120KMH, so if hes around 200 i bet he'd kill anything.or die instantly
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are all you asking is the forumula for momentum?
p=mv broheim
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On October 12 2011 07:21 turdburgler wrote:
are all you asking is the forumula for momentum?
p=mv broheim
Negative. Momentum wouldn't really apply here. (or, it would apply, but that's not what he's asking for)
Edit: And it doesn't apply here beyond any attempt at finding impulse b/c he's asking for the force with which he would hit (presumably) a tree, person, or the ground.
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Right, I wanted to say 55.(5), but then I decided to make it simple and just write 55.5. I fail.
@Risen: thanks, that does figure though, because with kevlar you still suffer from the force of impact but you only get superficial damage. Sorry, I was never good at physics. (which is odd cuz I like maths)
@telcontar: I was wondering what the force of impact would be... like.
So as Risen said, if it's ~41250N, I was wondering if someone could give me an example of a different collision with the same type of force (~40kN). Judging by F=m*a, it would seem that it's a similar impact as a 1000kg car hitting a wall while doing 14.4km/h. That doesn't sound TOO bad (but yeah, I realize that that's the force one would feel if he were between the wall and the car).
@tac0: haha, yes, I've seen that mythbusters episode. It has to be a really big bug though.
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55 m/s =/= 55 m/ s^2. Velocity does not equal accel.
The energy of impact would simply be 1/2 mV^2 assuming he has reached terminal velocity.
The energy of impact against earth is 113,473 Joules.
Determining the force of impact is a bit different.
The force of impact differs depending on:
1. The mass and velocity of object 1
2. The mass and velocity of object 2
A tree and a person are 2 entirely different objects. I also think that spring force would have some effect to the collision as well. The earth would be easier to calculate a collision against because you can assume the velocity of the earth after impact to be 0.
If you put in some more assumptions such as the time it takes for object a (the person) to go from 55m/s to 0 m/s (stopped) Lets call this the impact duration time.
Assume impact duration lasts .01 sec
Then you can calculate F= ma
where a = (55-0)/(.01-0) m/s^2 (ie 5500m/s^2)
Then the force of impact would be (75kg)*(5500m/s^2) = 412500N
But again this is against the earth where the earth 'absorbs' the whole impact and does not move as a result.
Hitting a person or tree involves center of masses, spring forces, object velocities, and object masses among other things.
Hope this helps.
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Not sure if it's right to say the acceleration is just from 55-->0 in 0.1s.
Isn't the force more like the air resistance he needs to overcome at the speed of 55m/s?
Which then would be k*v^3 where k includes air density, "cross section" etc and v is the velocity of the moving object.
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Let's take an average car and we'll assume 4000 pounds (google gogogo)
4000 lbs is about 1800 kgs according to a rough estimate in my head.
F = ma
41250 = 1800a
a = 22.91 m/s^2
If we take this and assume we're talking about a car crash. We work backwards.
Assume an average tim from point of impact to "rest" as .5s
at = v = 22.91m/s^2 * .5s (yup, that car ran headon into a brick wall that didn't even move, these things happen all the time in real life, or physics problems)= 11.455 m/s
So your guy falling from the sky is the rough equivalent of a car imparting ALL it's energy in a crash into a brick wall over half a second at 11.455 m/s or something like 25-26 mi/h. If this doesn't seem like a lot, REALLY think it through. Cars are pretty big, and usually a crash involves them gradually slowing down over the course of seconds, not HALF-seconds. Most crashes don't entail running into the immovable object, either. This is why cars have airbags on top of nature's natural tendency to have crashes occur in non-complete fashion. The longer you can have it take for that human eggshell inside the car to slow down, the better it's chances at survival.
A better example to give would be a car traveling at 45 mi/h crashing into a human. That's about 20 m/s. Human gets hit and slows the car by about .5m/s, how much energy is imparted on the human? We'll assume the human weighs about 70 kg.
NOW we bring in momentum. Find the velocity at which the human is now traveling, and make a baseless assumption about how long it took for said human to reach that velocity. (this doesn't even touch the fact that most humans "spin" away from car hits due to center of gravity issues)
p=mv now, car is p = 1800*20 before p=1800*19.5 after. We'll assume complete transfer of momentum (lol physics) 1800*20 - (1800*19.5 + 70*x) = 0 (Zero sum harharhar)
x is about 13 m/s
I've watched a few people get hit in my time. They get hit, and almost instantly go flying into cartwheels and shiz. We're going to assume the victim bent at the waist into a ball prior to being hit and is flying straight away from the impact (also, the car doesn't run him over because the driver used his brakes a little too late for our victim)
Time to accelerate to full speed: .1s
F = ma
a = v/t = 13/.1 = 130 m/s^2
F = 70*130 = 9100N
Yup, your skydiver is hitting with the force of 4.5 times my make believe, entirely unreliable, assumption filled, example.
Edit: Yup, this is probably riddled with errors. Someone come and fix it.
Double Edit:
On October 12 2011 07:36 Smoot wrote:
55 m/s =/= 55 m/ s^2. Velocity does not equal accel.
The energy of impact would simply be 1/2 mV^2 assuming he has reached terminal velocity.
The energy of impact against earth is 113,473 Joules.
Determining the force of impact is a bit different.
The force of impact differs depending on:
1. The mass and velocity of object 1
2. The mass and velocity of object 2
A tree and a person are 2 entirely different objects. I also think that spring force would have some effect to the collision as well. The earth would be easier to calculate a collision against because you can assume the velocity of the earth after impact to be 0.
If you put in some more assumptions such as the time it takes for object a (the person) to go from 55m/s to 0 m/s (stopped) Lets call this the impact duration time.
Assume impact duration lasts .01 sec
Then you can calculate F= ma
where a = (55-0)/(.01-0) m/s^2 (ie 5500m/s^2)
Then the force of impact would be (75kg)*(5500m/s^2) = 412500N
But again this is against the earth where the earth 'absorbs' the whole impact and does not move as a result.
Hitting a person or tree involves center of masses, spring forces, object velocities, and object masses among other things.
Hope this helps.
There should be an additional 0 on the 55. All you did was take my example and make impact time .01 instead of .1.
Triple Edit:
On October 12 2011 07:42 ZpuX wrote:
Not sure if it's right to say the acceleration is just from 55-->0 in 0.1s.
Isn't the force more like the air resistance he needs to overcome at the speed of 55m/s?
Which then would be k*v^3 where k includes air density, "cross section" etc and v is the velocity of the moving object.
No. We're not talking about the air resistance he's under at impact, b/c it's a nonfactor. The air resistance is what is keeping our example human falling at 55m/s instead of infinitely accelerating at 9.8m/s^2 to the ground.
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On October 12 2011 06:53 CubEdIn wrote:Hey guys. + Show Spoiler +So I was watching this video today of some insane wingsuit stunts, and discussing with a friend. I was wondering if I could find some terms of comparison of how hard this guy would hit something at that speed. I know that the terminal velocity for a human could get as high as 200mph, but say he's gliding and such, so let's assume that he's going 200km/h. That's about 5.5m/s. Say he weighs 75kgs or so. Is there any way to compare the impact between him and... say a tree or that guy holding the camera, and something else? I'm curious how devastating it would be. Said video: http://www.youtube.com/watch?v=TWfph3iNC-kLemme know what you guys think.
Mythbusters did something like this, didn't they? When they were testing a skydiver catapulting a kid off a seesaw? And they pretty much had to build a super-industrial strength seesaw to stop breaking things? And obliterated the dummy several times worse than usual?
Oh, and Lenovo recently did an ad showing one of their new notebooks with an SSD booting in freefall before it hit the ground to open a parachute. The one that didn't pull it off was pretty thrashed, and that weighs a lot less.
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Wow, thanks everyone for the replies.
@Smoot: thanks for the energy input, I was wondering what it is in Joules, as I know that's what they calculate projectile energy at the muzzle of the gun in. That's an insanely high number.
Yes, Risen, that does seem a lot stronger of an impact.
I can sort-of visualize it now, it's probably worse than getting hit by a decently-sized car going 100km/h. Wow.
@JingleHell: didn't see that one, but I'll look for it, and the lenovo thingamabob.
Thanks again for all the input, I didn't think so many people would be interested.
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200km/h is still something like 125mph. A human-being hitting any stationary, solid object with that much kinetic energy is going to leave a nice big, red stain in the local vicinity.
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Ahaha,oh man this topic reminds me of the time we were bored in physics class and calculated how many farts it would take to fill up the room and suffocate everyone in it.
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On October 12 2011 08:14 TheKefka wrote:
Ahaha,oh man this topic reminds me of the time we were bored in physics class and calculated how many farts it would take to fill up the room and suffocate everyone in it.
It's called applied physics and it's the best way to learn, cuz it's FUN! :D
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When I can go to a thread like this and understand even half of it, it feels like I'm not wasting my time going to physics class.
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EPT
