Me and my friends are discussing how hard the impact would be if you dropped a 250kg bench from 1m down on yourself.
Come on nerds I need help.
>>37369656
It would be 12 force
>>37369656
It would be very painful
>1m
>>37369656
Shit heavy
>>37369672
4 u
F=ma
High school physics
f=ma
m=250kg
a=9.8m/s^2
9.8(250)=2450 newtons
thats a lot of force
>>37369656
24,5 kN (don't know how much it is in freedom units)
It would hurt
>>37369727
do you wanna know how i can tell you are retarded?
>>37369742
I do!
>>37369742
yes
>>37369672
You're a big guy
Why does that even matter if you count the force, OP. You want to know how hard the impact would be? I t would crush your ribs, sternum, and could puncture lungs. In any way, you very likely end up from internal bleeding.
>>37369656
It's a quarter of a ton in the form of a very narrow barbell landing on your ribcage
you'd suffer very severe injuries.
>>37369794
end up dead*
Yea, but we got different answers, we were kinda wondering what the impact would be in kg?
Like it would be the same ass laying xkg on you.
one of us actually got 245kg, which means on the way down it lost 5 kg.
>>37369727
Moron.
>>37369656
Which body part are we talking?
>>37369834
>on the way down it lost 5 kg
Are you retarded? Try catch a 2kg stone from 30 cms and then try catch the same stone thrown from Eiffel tower.
>>37369886
I know, one of my roommate fucked up his calculation.
got 2450N I know it's wrong, but I was more looking for the correct so we could compare.
I got 500kg not sure if that's right.
>>37369834
I'm not a native english speaker so excuse my shitty knowledge of terms.
Let's consider that the barbell's base is rectangle with about 4 cm width and 60 cm lenght (width of your chest).
That gives 0.024 m^2
Pressure=Force/Surface
In first case, a laying barbell applies 2500/0.024, which is 104166 Pa
When it's dropped (I used other anon's calculation of force not to bother) it's 122500/0.024, which is 5104166 Pa.
That is 49 times more pressure, which is like keeping 12250 kg on your chest for a short while
>>37369656
If you're talking strictly about force, then the distance doesn't matter. It's simply:
a=F/m
F=ma
F=(250)(9.81)
The guy above me isn't "retarded." According to Newtonian mechanics, this is literally the only force acting on a free falling object.
It would be better if you specified what "impact"
If we're talking about elastic kinetic energy during impact of a moving body and still body, then sure, it's not as simple as F=ma.
Since in a perfectly elastic collision, no kinetic energy would be lost, this isn't an elastic.
collision. There is energy being lost to heat and sound.
However, let's assume this is an elastic collision between the falling barbell and your body.
Then still, the distance doesn't matter as:
delta0.5mv^2 of initial = delta0.5mv^2 of final
If we want to find the kinetic energy during the impact:
KE=0.5(mi+mf)vf^2
If we want to find the energy lost to friction:
E=7.5u(mi+mf)g
Ultimately, we can't know unless we know the velocity. But one thing certain: height literally has no impact on neither kinetic energy, energy lost to friction and force.
People are getting this all wrong. It depends on how much your body compresses and how long it takes for the falling bar to come to rest.
lets say the weight decelerates fully in 0.01 seconds and your chest squishes by 0.1m as a consequence
via SUVAT
distance = -0.5at^2
0.1 = - 0.5a x 0.01^2
a = -(0.1)/(0.5 × 0.0001)
a = 20000
F = ma
F = 250 x 20000
F = 50000000N
so thats 50 meganewtons, and you are dead.
>>37369886
>>37369656
Comparing to lighter object falling but with longer drop gives some perspective of the force applied.
250kg weight from 1 meter is equivalent to 25kg weight dropping from 100 meters
>>37369672
*extremely
jesus christ do you even banepost
>>37370001
>>37369727
THE ACCELERATION IS NOT 9.81, THE ACCELERATION HERE IS IN REFERENCE TO THE DECELERATION PROVIDED BY THE BODYS RESISTANCE TO MOTION
YOU ARE FINDING THE FORCE ON THE BAR THAT CAUSES IT TO FALL
25000N is the same as just resting the bar on your chest - obviously a bar that has fallen 1 metre already has MUCH more force behind jt
>>37370002
see this. we dont know the crucial variables here.
Here is my shot at this fun mess:
v^2=u^2+2as
So the speed that the bar hits you at should be about (2(9.81)(1)^(1/2) = 4.4 ms^-1
Ek=1/2mv^2 , so the force of the cunt hitting you will be 1/2(250)(4.4)^2 = 2420J
No idea what that means but I'm sure 2400 is a big-ish number so I'm sure it would fuck you up
>>37370021
no its fucking not
>>37370052
nice try, but thats simply the energy expended to bring the falling object to a halt. it isnt the force.
>>37370052
It's roughly the amount energy required to push a large suv 1 meter
>>37369656
It would fucking kill you
https://www.youtube.com/watch?v=rgYDfporX00
I took part in it, but I knew these discussions always end up in a shitfest on 4chan. This is pretty fun, but the easier the equation the better.
>>37370052
>>37370095
energy means nothing for this purpose. We need to know over what time period that energy is expended.
to use your example, pushing an SUV very slowly for an hour is a low force over a long period of time - if I punch an SUV so fast it goes flying and my punch lasts half a second its the same energy but millions of times more force. To say that "this energy is the same as pushing an SUV" makes no sense unless you explain for how long and how far you are pushing said SUV.
You need to know how fast this energy is being "used".
>>37370021
>250kg weight from 1 meter is equivalent to 25kg weight dropping from 100 meters
what?
No, it really isn't.
Head, throat or chest?
>>37370037
So let me get this straight, the OP is asking if the barbell fell on you as you held onto it in a bench position? So basically like a failed bench press?
I thought he was asking if it just fell from 1m above him or something without him touching it.
Take a look at my drawing. Pretty sure these are the only forces acting on the barbell. (F1 is the force the person is acting). Did I miss any other force?
>>37370055
>>37370160
It is. This is basic high school physics.
>>37370237
No, he is just asking about if its just dropped from 1m above the guy.
>>37369656
>1m
u ded nigga
Someone get /sci/. We need an adult.
They are right about impact force being its own thing though.
>>37370247
Your basic multiplactive maths is just shit.
A 25kg weight at 100m is really about the same as a 2500kg weight at 1m
>>37370265
im trying to fucking tell you guys this shit. The answer is >>37370002 ffs.
You guys are morons... Here is how you calculate it:
Get the speed of the bar prior to deceleration (~4.4m/s).
Estimate the time during deceleration (0.4s).
That gives you the impulse of deceleration and from that the 'stopping force' applied by the body.
Then apply the force by the area of the barbell to get the pressure.
Then speculate about the rate of rate of change of momentum of the barbell which probably magnifies the peak pressure by about 1.5.
Short answer: it will fuck your shit up.
I too am curious about what would happen. I have a home gym in the upper floor of my my 2 story 1960s suburb house. What would happen if god forbid I fail a 405 deadlift?
>all these people calculating the weight of the barbell as if that's the answer
L o l
The "a" part of f=ma is the acceleration that occurs when your body has to stop the bar that has landed on you. It's a really high number, but not going to be easy to calculate without lab work. The anon who posted about conservation of energy probably has the best solution.
>>37370248
>>37370002
Ok then let me start by saying:
"distance = -0.5at^2
0.1 = - 0.5a x 0.01^2
a = -(0.1)/(0.5 × 0.0001)
a = 20000"
is wrong. If the object is in free fall, the acceleration is constant 9.81.
This is because the kinematics equation you used can only be used for rectlinear motion which states 1. you must have an initial velocity at time = 0s and 2. the acceleration must be CONSTANT.
If we are assuming there is a deceleration (which there isn't, because it's in free fall) then we can't even use the kinematics equation because it's not a rectlinear motion.
>>37370334
That was good until the final paragraph.
Rate of rate of change of momentum is just the rate of change of the force, which isnt relevant over a tiny space of time, and certainly doesnt increase pressure by 150%.
>>37370365
The object is not in freefall. The acceleration mentioned here is the DECELERATION from the bar hitting the guys body - g doesnt come into it.
does that make sense?
>>37370365
Stop it you mong
>>37370365
>there isnt a deceleration
then how come the bar stops, dummy
>>37370386
I just meant to imply that the deceleration impulse applied by the body to stop the barbell is hard to predict, meaning the forces generated are varying with time as the body decelerates the barbell: a human chest is neither a spring or a damper and has a complicated plastic/elastic response to strain.
>>37370456
Yes, calculating the deformation and stress patterns of the body after the impact would be difficult. But we dont care about that, we only want to know the total force on the human's body.
And for that we can just use conservation of energy by finding the work done and so neatly bypassing all the fiddly work youre talking about.
its important youre careful not to overcomplicate things uneccessarily.
>>37370423
barbell guillotine
barbell stops on the bench
>all these f=ma highschool fags
Do you even strength of materials?
>anons that are using 250kg as the mass
>>37370529
it is the mass though, you're thinking of weight
>>37370237
>>37370002
This is why I cringe when YouTube fags do a thumbs over grip on a bench press
>>37370529
it is the mass of the object, yes. Nothing wrong with that.
>>37370528
you are overcomplicating things just as they are oversimplifying them.
Strength of material is irrelevant as we only want the total force over the whole collision.
W = F x d, SUVAT, F = ma and conservation of energy are sufficient.
http://hyperphysics.phy-astr.gsu.edu/hbase/flobi.html
the force at the moment of impact is 24500N, this is ~2500kg
the approximate equivalent would be holding two average cars on a few inches of your chest/neck/head, before your body begins to "stop" the weight
>inb4 cheater
fags
>>37370386
I understand what you're saying but I think in order for us to move forward, you should explain why you think the object is not in freefall.
The premise states a barbell is simply dropped 1m above a guy.
Given the premise, the only force there is gravity. There is no normal force or applied force.
If you mean the force at impact, the deceleration caused by impact would have no change on the initial force of the collision.
Yes the object would decelerate, but only after it exits free fall.
Don't take this as patronizing from me, I mean no offense to your intellect. I simply want to know the reason why it's not in free fall.
>>37370423
There is a deceleration AFTER impact. This doesn't change the acceleration up until the initial impact.
How far up the chest does it have to land to change the sound from a grunt to a strangled squeal?
For science...
>>37370563
they arent dropping it from a metre, more like 0.4m
Still fatal, but less messy.
>>37370571
Hyperphysics makes an assumption about the impact time, but its a perfectly good approximation I suppose.
>>37370583
You are finding the force exerted on the falling barbell by gravity. This is because the acceleration you use (g) is from gravity.
We want to know the force that the barbell exerts on the man. This force is the equal and opposite reaction force to the force the man exerts on the barbell. So we just find that to make things easier.
The force the man exerts on the barbell is not composed of g, but of the deceleration caused by him getting squished.
>>37370605
Actually its during the impact, not after. In fact the decelerational period is what we define as the impact.
>>37370628
Squeal comes from hitting the diaphragm. So as long as its below the sternum, it should make a squeal.
>>37370571
that's prob the closest estimation in this thread
>>37370646
Squeal was the wrong word to describe the sound... I'm thinking more along the lines of that high-pitched warbling fart sound you get from pulling on the end of an open, inflated balloon.
But his chest is the balloon and the bar is crushing his larynx into a balloon end.
>>37370237
well you haven't taken into account the distance at all, only the force acting on the bar to cause its acceleration. what you have figured out is true but its meaningless/useless in terms of what OP is wondering.
we would need the speed of the bar, which we can get.
W = F*d. assuming W=K, K= 0.5* m * v squared. now we have the speed at which the bar hits the poor dude. suicide grip, not even once.
now, if we know how much the bar compresses his body (lets call it 0.15m judging by OP's pic), then we can find the impulse, F*t = F*d/v, which happens to come out as 83 N/s, which is about the same as the impulse of a ford focus crashing into a brick wall at 3mph. so its gonna be a pretty intense hit to his body.
>>37369656
OP: "No, I most certainly cannot do math."
>>37370631
Okay I got what you're saying but if that's the case, we can't use "distance = -0.5at^2" to figure out our acceleration because it wouldn't be a rectlinear motion.
(I don't know if you're the one who did posted that equation above).
Even if we know the distance and all of the variables, we still can't use the kinematics equation to plug it into "F=ma" because once again, the one dimensional kinematics equations are only true for rectlinear motion.
So this isn't really a case of "we don't know the variables" but rather, we can't apply one dimensional kinematics to solve this.
>>37370819
It is effectively rectlinear motion, because we only consider the vertical component of the bar's motion. This obviously acts in a straight line, so we can use the kinematic equations.
>>37369656
I wonder how often people seriously injure or die because of falling barbells. It kinda scares me.
>>37370838
But the premise was already stated that the acceleration isn't constant so effectively we can't use the kinematics equations.
>>37370001
>height literally has no impact on kinetic energy
wew m8
1. get a stone as big as your fist.
2.drop it on your head from 1mm
that shouldn't hurt
3.now drop it from 1000m
since kinetic energy is the same from every height it should be the same impact right?
FUCKING IDIOT PIECE OF SHIT FAGGOT FUCK OFF
>>37369672
You're a large guy
>>37370819
the horizontal motion, the rotation etc is going to be so small that it just doesn't matter for the purposes of this thread. we're already in a position of having to approximate, whats a few joules here and there
This is an impact force from a falling object equation from http://www.engineeringtoolbox.com/impact-force-d_1780.html
So, with a 250kg of weight (mass) and 1m of height we can use the equation below to solve for the impact force oof a falling object
F = m g h / s; where F = impact force, m = mass of object, h = falling height, g = gravitational constant, and s = "slow down distance"
The only thing we need to assume here is the slow down distance which should be measured empirically but we can make an educated guess on; a normal chest compression on the drop of the weight could give us about an inch (2.54cm) when benching normally so its safe to say that a two inch compression after a huge drop like that would be "normal" (I have no fucking clue what it is actually is) which gives us about 5cm or .05m.
So, we end up with:
F = (250 kg) (9.81 m/s^2) (1 m) / (0.05 m)
Which gives us:
F = 49050N or 49.050 kN
Turning this into freedom units adds up to about 11015 lbs-f. This is a lot of fucking force to drop on your chest, equivalent to the weight of a big ass truck standing on your chest.
Or the equivalent of how much force your dads dick has when it penetrates your tite boipucci every night before you go to bed.
>>37370583
so 250kg, 1m high
mgh = 250kg x 9.8m/s^2 x 1m
= 2450 kgm^2/s^2 (joule)
at 0m, all potential energy converts to kinetic energy
1/2mv^2=2450 joule
lets say that barbell's slow down distance is 0.01m, a centimeter.
impact force would be 2450/0.01 = 245 000 joule, which means 245kJ
which is alot.
you'll get you shit fucked up. basically every bone in your chest that makes contact with the bar gets fractured, eg. sternum
>>37370895
whelp wrong >>, meant to reply to op
>>37370876
?
Yeah I said nothing about potential energy though.
Strictly talking about force, there is no change in force whether it's dropped from 1m or 1000m.
I'm sure you've heard of the famous Galileo's leaning tower of pisa experiment where he dropped a feather and a stone to see which dropped faster. The entire experiment proved acceleration (gravity) is constant.
If the mass is the same, the force wouldn't change whether it's dropped 1mm or 1000m.
>>37370919
OP asked about the impact
you are on the wrong rails m8
>>37370889
oh forgot
source: just finished mechanical engineering degree
>>37369672
you're a man of great mass
>>37370889
>>37370956
>mech eng degree
>can't into the simplest kinematics
>has to use premade equations
i guess you wasted some time man
>>37370986
>doing actual math work outside of school
thats not what we do in the real world desu senpai
Some of the impact would be dissipated by whip in the bar.
>>37370889
hi five for getting the same answer bruh (>>37370002)
Can someone screen cap this and call it "when gym retards try to solve a physics problem"? Thanks.
The barbell reaches a speed of 9.8m/s.
We assume it takes about 0.01m to slow down.
u =9.8
v = 0
s = 0.01m
v^2 = u^2 + 2as
a = -9,8^2/(0.02) = 4802 m/s^2
F = ma = 4082*245 = 1000090 or 1MN
Now, this is the FORCE.
We want pressure.
Say his body is 0.4m across.
The barbell is 0.05 m in diameter
the impact area is 0.020m^2
pressure = F/A = 50MN/m^2
The shear stress of bone is about 51MN/m^2 normally.
So basically there's a very good chance he's fucked himself.
Source: mechanical engineer.
>>37371055
>math work
did you just compare math with mechanics?
triggered me a bit
>>37371144
Wow, I really needed to know you were a mechanical engineer or I would have never believed that you were using basic equations of uniform motion and newtons second law.
>>37369656
What is "how hard"?
The force on your neck?
The momentum of the bar when it hits?
The kinetic energy of the bar when it hits?
I'm an actual physics major but I can't answer a vague question.
If you're asking "how much would it hurt" the answer is "a lot", but if you're asking some serious I gochu.
>>37371191
i want to punch your fucking teeth in for being such a cocky fuck. then i'd suck your toes.
you can't answer this question. the bar would have to travel for a certain distance AFTER the impact to figure out the "Impact Force". I guess that would depend on how hard his skeleton is
the kenetic energy is 2450J
the velocity of the bar at impact is 4.4m/s
>>37371144
You took into account the diameter but not the width.
>>37371234
so make sensible approximations, dummy
>>37371153
He asked why I wasn't deriving my own mechanics equations using math because I instead referenced a website for the formula. Mechanics uses math so stop worrying about semantics faggot.
12250N assuming it would sink 20 cm into your chest
It's smaller because your chest is considered elastic
http://hyperphysics.phy-astr.gsu.edu/hbase/flobi.html
velocity at impact mutlplied by mass to give impulse?
>>37370565
No. You can't tell how something breaks unless you analyze the stress/strain.
>>37369740
Your arms are a meter long?
>>37369763
For you
