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/sci/ - Science & Math

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2035496 No.2035496 [Reply] [Original]

Dear /sci/

I'm trying to tell somebody why this wouldn't work but I'm having a hard time explaining it.
Could you guys explain why it wouldn't?

>> No.2035502

Friction

>> No.2035500

friction, gravity.
/thread.

>> No.2035503

The valves don't exist IRL because they are impossible

>> No.2035505

Because fuck you thats why

>> No.2035506

>>2035500
>>2035502
>>2035503

These are cop-out answers

Assuming a "perfect" machine where the seals are efficient as possible, why wont it work?

>> No.2035514

nobody in /sci/ can answer this question

>> No.2035520

>>2035496
Isn't this just a ass backwards water wheel except horribly inefficient? This is plausible in some fashion though.

A better troll pic is standing in a bucket while trying to pick yourself up in it.

>> No.2035528

water generates pressure on the valves, who in turn press on the air-filled balls, stoping them.

>> No.2035533
File: 56 KB, 900x600, insane-clown-posse.jpg [View same] [iqdb] [saucenao] [google]
2035533

fucking perpetual motion: how does it work?

>> No.2035535

because there's space between the balls of air and water will leak out.

>> No.2035537

>>2035528
but by making the tube longer you could fit more bubbles in it, overcoming the resistance.

>>2035520
a water wheel require moving water, this does not.

>> No.2035538

inertia

>> No.2035539

>>2035506

water pressure at the bottom valve would be too much for the mechanism to overcome.

>> No.2035543

>>2035537

longer tube means more water, and thus more pressure.

>> No.2035544

>>2035539

see

>>2035537

>> No.2035549

>>2035537
In concept its a similar IDEA to the water well. The air is what you propose is moving. As opposed to the water.

I think using gravity and the nature of water you could make a waterwheel without needing a river.

>> No.2035560

>>2035503
dumb
>>2035520
dumb
>>2035535
dumb
>>2035538
dumb
>>2035537
dumb

jesus, have none of you people ever drawn a free body diagram before? even with an ideal valve/diaphragm thing at the bottom, this isn't plausible because of how buoyancy works. consider a ping pong ball halfway through the valve; i.e., half is in open air, half is under water. there is no upward force on this ball; rather, the surface integral of pressure on the ball has a net downward force. as opposed to a fully-submerged ball, where, due to greater hydrostatic pressure at greater depths, the net force on the lower half of a ball is greater than the net force on the upper half of the ball, creating buoyancy.

and because of increased hydrostatic pressure at depth, this means that the pressure holding down our half-submerged ball is going to be greater in magnitude than the upward force on the bottom half of the ball above it.

ib4 "gay engineer", fuck off, sorry i can actually solve problems.

>> No.2035573

>>2035560

No, third rate engineer. Your model is lacking the other four submerged balls above the ball at the ideal valve, which combined would create a net upward force on the ball at the valve.

The real answer is this:>>2035539 , hydrostatic pressure > buyoancy of some measly balls.

>> No.2035575

>>2035560
Ok, but why is >>2035535 dumb?

>> No.2035584

>>2035573
>No, third rate engineer. Your model is lacking the other four submerged balls above the ball at the ideal valve, which combined would create a net upward force on the ball at the valve.
No, you fucking idiot. it's called induction. my "model" accounts for an infinite number of balls.

>The real answer is this:>>2035539 , hydrostatic pressure > buyoancy of some measly balls.
While that guy is partially correct, there is no need to bring the magic valve into this. The surface integral on a valve of any shape there is going to have the same net force as the force on the ball itself. lrn2 calculus.

Also, you're still a doubleidiot because hydrostatic pressure IS what creates buoyancy.

>> No.2035587

>>2035573
but lets treat this like any physics problem you would find in a text book:

assuming a PERFECTLY EFFICIENT MACHINE, why would this not work?

...would it work?

>> No.2035595

>>2035575
>Ok, but why is >>2035535 dumb?

Well, it's good that you're thinking physically... yes, there can be no such thing as an ideal valve/diaphragm like that which would keep water from leaking out. but that also doesn't really answer the question -- e.g., could that string of balls still move at all, even if water was slowly trickling out? the answer is no.

considering an ideal case of a magic force-field type frictionless diaphragm on the bottom which holds all water in and exerts no extra force on a ball besides that which the water already does, the balls will still cease to move.

>> No.2035601

>>2035587
assuming perfect efficiency is like assuming 2+2=5

>> No.2035606

>>2035587
NO IT WOULDN'T FUCKING WORK. I already explained why here: >>2035560

Even with 100% efficient/frictionless components, there is no way for buoyancy of the fully submerged balls to pull another ball into the bottom of the chamber.

Let's think of this a bit differently... what if, instead of water, that tank had a different fluid, with a different density? If the fluid had double the density of water? what if it had half the density of water? would the balls move faster or slower?

>> No.2035608

>>2035595
i understand your reasoning, but is there not some possible arrangement of balls that could overcome the resistance of the bottom most ball?

What if the balls were arranged in a spiral, adding even more submerged balls to the "chain" while keeping only one ball at a time waiting to come into the chamber?

>> No.2035610

>>2035587

Physics problems usually don't assume 100% efficiency, per se.

They assume zero friction, zero air resistance, and zero of anything else that's small in a given context.

In this case, all of the factors limiting efficiency would be far from negligible.

>> No.2035615

>>2035601
NO, HOLY SHIT, HAVE YOU NEVER TAKEN A PHYSICS CLASS IN YOUR ENTIRE LIFE? ALL CAPS.

idealized cases like frictionless environments are useful because they can give insight into what are the most important mechanisms in a physical situation. this is self-evident here by realizing that even with an "ideal" case, the fundamentals of fluid mechanics prevent this from happening.

>> No.2035621

>>2035584
Well It was implied that I was talking about the hydrostatic pressure on the valve, I didn't think that required explanation to some one who should know what they are talking about.

Your model doesn't account for infinite balls in mathematical terms, only the effect of water pressure as it tries to pass through the valve, or so is stated in your post. The limiting part of the mechanism would be the opening of the valve, before the ball can even pass through. Logic says that it wont work, but a mathematical proof can be made by developing a function which relates the boyancy of any number of balls to the depth of water and then showing that the pressure on the valve is always greater than the force of the balls.

This is essentially what you implied, but did not directly state and you didn't examine exactly when it goes wrong, the ball will never get halfway into the valve.

>> No.2035623

>>2035608
you clearly don't understand the reasoning. it does not matter how many balls are in the tank, because bottom ball you're trying to draw into the tank will always have more downward pressure than the sum of all the buoyant forces acting on the balls above it.

>> No.2035628

>>2035560
this guy is right.

also, each ball loses energy as it rises through the water from drag. so not all of the potential energy each ball has at the bottom of the tank gets converted to kinetic energy. even if you set this into motion by hand, it would slow to a halt pretty quickly.

>> No.2035629

>>2035560
can't explain it = don't understand it = engfag

>>2035539
this is also right. the ball leaving the tank is balanced by the ball entering the tank at the bottom, so nothing changes and the system doesn't move. this is obvious if you use infinite continuous balls.

>> No.2035645

>>2035629
That's not what that guy is saying, don't pretend to understand what he's talking about because then it will only make you look like an even bigger idiot when you explain it wrong.

>> No.2035649

>>2035621
i'm not going to write a goddam proof on sci to a bunch of undergrads and other assorted teenagers that wouldn't even understand the basics of a free body diagram.

i can certainly write a proof, and it works for infinite balls by induction. consider the balls as a sequence of hemispheres... the downward force on the upper hemisphere of one ball will always be stronger than the upward force on the lower hemisphere of the ball above it. because the bottom partially-submerged ball has no upward force on it, it's downward force is stronger than all combined effects from above.

actually, the induction can be even stronger than that. instead of a string of balls, it can actually be a single ball with the same combined volume displacement. a single large ball halfway in the bottom of the tank will not rise, therefor a million smaller balls strung together also will not.

>> No.2035663

>>2035645
ok, what's he saying? the force on the valve is only stopping the bottom ball from entering. what other mechanism is there?

>> No.2035669

>>2035628
>this guy is right.
i know i am! i'm the aerospace engineering phd candidate that posts on occasion. i *do* fluids.

>also, each ball loses energy as it rises through the water from drag. so not all of the potential energy each ball has at the bottom of the tank gets converted to kinetic energy. even if you set this into motion by hand, it would slow to a halt pretty quickly.
sorry no, drag is not a factor here. why i explained this won't move also holds true for an inviscid flow.

if you were to set this in motion and watch it slow to a stop, you could call that effect at the bottom "form drag" if you wish, but i wouldn't. what's telling is that if you have this stopped, and release it, it will not move. i.e., it's not drag that is stopping this from moving.

>> No.2035671

>>2035537
The deeper the tank is the greater the pressure, lol. Lrn2Statics.

>> No.2035678

>>2035649
I just realised your model is wrong because the solution "the surface integral of pressure on the ball has a net downward force" proves that the system will actually run backwards, ie the balls will indefinately spin clockwise on OP's diagram... that is until you analyse the case when the ball has passed down through the valve,... which is what my answer does from the beginning.

GG.

>> No.2035692

>>2035587

The balls cannot create a force to make the chain go down. Ever notice how if you hold a loop of chain by your finger it just kinda sits there limply? The same gravity that holds the water in place also holds the balls in place. If you could create a field where there was no gravity on the upward side of the model but retained gravity on the downward side, you might have something.

>> No.2035700

>>2035678
i'm aware that the equilibrium point for the system is going to be with the waterline of the bottom ball somewhere between its equator and its north pole. i was giving basic logic for the fundamental mechanism of this device's failure understandable by the morons posting in this thread. nobody needs a dipshit tryhard like you to fumble around and try to piece together an answer.

if you want to prove me wrong mr. dipshit tryhard, determine where the waterline will be for the bottom ball. it's a pretty simple application of very basic differential equations. i'll wait.

>> No.2035701

>>2035669

i'm not following how drag doesn't play a role. i guess the shape/velocity of the balls wouldn't do much to reduce velocity so it's not an important factor, but isn't drag present in inviscid fluids?

>> No.2035712

>>2035692
lolwat

hold a chain up with your left hand. with your right hand, pull down on the bottom of the chain. herp a derp, you just discovered a way to force the ball/chain/string down.

and gravity has 0 effect on the situation, since it's symmetrically acting on both the upward and downward sides of the chain.

>> No.2035736

>>2035701
>i'm not following how drag doesn't play a role. i guess the shape/velocity of the balls wouldn't do much to reduce velocity so it's not an important factor, but isn't drag present in inviscid fluids?

the only drag in an inviscid fluid is wave drag due to compressibility, i.e. things like transonic effects. in a real case, yes, these balls will be experiencing some amount of viscous form drag. but consider the example i gave of the balls starting at rest. if you have no motion, you have no drag, right? yet the chain will resist movement.

>> No.2035753
File: 91 KB, 800x600, 1288380136233.jpg [View same] [iqdb] [saucenao] [google]
2035753

Dear /sci/

Maths proves this to be true, why doen't the army use it?

>> No.2035754

>>2035700
There will be no waterline fuckwad, you're assuming some kind of magic force field which only lets the ball pass through by opening up like an asshole and somehow ignoring hydrostatic pressure, which is not necessary to disprove this. Relate the dimensions of the ball to the area of the valve, treated as a regular planar valve, not some magic asshole, and you will see that the pressure on the valve is always greater than the buyoant force of the balls of whatever size.

Simple, also no I'm not going to relearn differential equations to make some proofs for a failure of a phd candidate. I'm third year mechanical, fluids isn't even my thing and shit did I show you.

>> No.2035797

>>2035754
>also no I'm not going to relearn differential equations to make some proofs for a failure of a phd candidate. I'm third year mechanical
>third year mechanical
>relearn differential equations
>implying that differential equations is something you can just forget about and succeed in harder engineering courses
>fluids isn't even my thing
>implying fluid mechanics isn't fundamental to mechanical engineering


>you're assuming some kind of magic force field which only lets the ball pass through by opening up like an asshole
right, that's the problem statement.
>somehow ignoring hydrostatic pressure
lolno. i'm most definitely not ignoring hydrostatic pressure.
>There will be no waterline fuckwad,
incorrect. at equilibrium, the bottom ball will ABSOLUTELY be partially above the bottom of the water tank. if no ball is partially submerged and partially below that border, there will be upward motion. the waterline for that bottom ball can be found with a similar analysis to finding the water line of any floating object on the surface.

you sure did "show me", tryhard.

also, to reiterate,
>implying that differential equations is something you can just forget about and succeed in harder engineering courses
HAHAHAHAHAHA. what is your "mechanical" program? how to pump gas for real engineers? what classes are you taking that don't require differential equations? you must not be taking thermodynamics, fluid mechanics, material sciences, mechanics of materials, dynamics, ...

>> No.2035866

>>2035797
Ok, maybe I exaggarated the relearning part, but you only use relations already proved by long dead people. Not what I would call using differential equations, more like plugging in numbers and using some basic calculus to solve pointless problems.

Equilibrium does not require the bottom ball to be above the bottom of the tank if you treat the valve like a translating plane, which is all that is required to completely disprove the idea. Your solution requires more work than necessary to prove beyond a reasonable doubt that it will not work.

Fluid mechanics is necessary, but not as fundamental as it is for aero, same as electronics to electrical etc. Otherwise we would've learned this shit earlier to have a better fundamental understanding of it.

>> No.2035979

>>2035866
>Ok, maybe I exaggarated the relearning part, but you only use relations already proved by long dead people. Not what I would call using differential equations, more like plugging in numbers and using some basic calculus to solve pointless problems.
Holy mother of god no. differential equations are how you solve real, physical problems. it's not about plugging and chugging some bullshit into formulas, it's about actually coming up with the formulas. that's just goddam sad that you actually feel that way. either your instructors have failed you, or you have failed them. have you never solved a problem that had never been solved before? if you're presented with a difficult physical problem, and you can't find a formula for it, what do you do? like in this example, right here, you're not going to find an explicitly written formula. but what you can do is take some very basic principles of fluid mechanics combined with the mathematical tools of differential equations, and come up with an elegant answer that solves an interesting problem. this is the joy of engineering.

do you honestly think you will get a job where someone will hand you a problem set, and a list of equations, and tell you to plug and chug? of course not. you'll be given problems to solve because they haven't been solved before.

>> No.2035983

>>2035866

>Equilibrium does not require the bottom ball to be above the bottom of the tank if you treat the valve like a translating plane, which is all that is required to completely disprove the idea.
What on earth do you mean a "translating plane", like a plane that pushes up into the water? 1) that's basically the same thing, but 2) that'd still be part of the ball pushing into the chamber of water. without the ball penetrating the water at all, you have no hydrostatic pressure acting on it, and there will be a net buoyant force upwards. equivalently, a ship cannot float on top of the water without displacing water.

i assure you that equilibrium *absolutely* requires that some part of the bottom ball be submerged in the water. there will be a waterline, and you can find it, if you think about it, instead of looking for a magic formula.

>Your solution requires more work than necessary to prove beyond a reasonable doubt that it will not work.
nonsense. everything should be made as simple as possible, but no simpler. if i were to assign this problem to a class i taught (next time i lecture on fluid mechanics i'm totally putting this on an exam), a correct answer would only need to use the principles of hydrostatics, gauss divergence, and very elementary diffeq.

>> No.2035999
File: 47 KB, 711x695, TROLL FLYING.png [View same] [iqdb] [saucenao] [google]
2035999

You all think you're so smart.

Try to disprove THIS.

>> No.2036016

The total force of a ball rising through the water is less than the force required to overcome the pressure of the water and push the ball into the water.

>> No.2036019

>>2035999
Orbits?

>> No.2036021

>>2035999
Air resistance will cause you to slow down and fall to earth.

>> No.2036029
File: 63 KB, 1246x927, asdf.jpg [View same] [iqdb] [saucenao] [google]
2036029

From wikipedia:
The "Float Belt". The yellow blocks indicate floaters. It was thought that the floaters would rise through the liquid and turn the belt. However pushing the floaters into the water at the bottom would require more energy than the floating could generate.

>> No.2036044

>>2035983
The net buyoant force on the ball will ultimately be applied to the valve as the ball tries to push it up (translation not anus like opening), so you do a FBD on the valve, force of buyoancy vs hydrostatic pressure. Hydrostatic pressure on the valve will always be greater, hence valve will always remain closed. No need for the bottom ball to even be partially into the water.

Of course this is not valid if you're a dick and say that the valve must be treated like an anus which will never happen in reality. But it's not like the type of questions instructors come up with are ever based on reality. I.E. using a shitload of complex relations to come up with a guess for something trivial when in reality you'd take a fucking ruler to the thing and measure it.

>> No.2036046

The history of troll physics
http://en.wikipedia.org/wiki/History_of_perpetual_motion_machines

>> No.2036050

>>2036021
Air resistance will cause you to burn to a crisp and fly apart in a burst of ashes.

>> No.2036072

>>2035999
The international space stations orbiting speed is 7.7066 km/s, the speed necessary to attain orbit off of mount everest is significantly greater than this. No projectile within the atmosphere will travel this fast, only rockets will....and that costs several billion dollars for a flight lasting a few minutes.

>> No.2036075

>>2035505
hahaha