Really 'interesting' puzzle

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  • Deleted user 15 October 2013 20:53:20
    https://plus.google.com/100806530036395598430/posts/3aHa4RPgtTT
    At first I thought that the side with ping pong ball would rise. Then after reading more I thought it would stay the same. Now my head is all over the place. ARRGGH!
  • Deleted user 15 October 2013 20:54:33
    My head hurst because there are duplicate threads.

    Which do I post in?

    OMG, razors on aisle 3, stat

    ed:heh, speedy tidy up

    Edited by Ironlungs76 at 20:55:26 15-10-2013
  • X201 15 Oct 2013 20:55:57 15,228 posts
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    Left will drop.
  • phAge 15 Oct 2013 21:16:47 24,344 posts
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    Left will drop, as the steel ball doesn't affect the weight of the right beaker, while the ping pong ball weighs down the left side ever so slightly.
  • Carlo 15 Oct 2013 22:04:36 17,987 posts
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    They are on my balls

    PSN ID: Djini

  • Deleted user 15 October 2013 22:35:55
    This did the rounds a while ago. The right side will drop because physics.

    In both beakers the same amount of water is displaced.

    In beaker A there's an extra upwards force due to the pingpong ball weighing less than the displaced water, but also being attached to the beaker.

    In beaker B there's no additional force, up or down.

    The easier way to think of it: Remove the water and make the ping-ping ball lighter than air.
  • Deleted user 15 October 2013 22:42:06
    PS - that is the absolute correct answer, so if this descends into more planes on a treadmill bullshit I will stab someone.

    Edited by meme at 22:42:23 15-10-2013
  • Trowel 15 Oct 2013 22:45:42 17,531 posts
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    meme wrote:
    PS - that is the absolute correct answer, so if this descends into more planes on a treadmill bullshit I will stab someone.
    That's what she said.
  • Deleted user 15 October 2013 22:55:20
    THAT BEING SAID I am now second guessing my own explanation (in that it's less a case of the ping pong ball pulling up but the buoyancy of the steel ball pushing down as it's an external system, rather than a balanced internal one), although the answer is still that the right side tips, so balls to any further meandering.

    Answer: Physics.
  • Bremenacht 15 Oct 2013 23:30:34 17,687 posts
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    Actual volumes remain the same, so I'm guessing they balance.
  • Deleted user 15 October 2013 23:41:27
    They balance if the buoyancy force of the steel ball/beaker B system and the mass of the pingpong ball and the string are the same, but they're not so they don't.

    I still suggest getting a bucket of water and trying it yourself. Put bucket of water on scale. Tie object denser than water onto string. Lower object into water. See change in scale. If change in scale > weight of ping pong ball and string, it tips right.

    I've given up trying to reason the actual explanation in words resembling English, but it requires pretty solid knowledge of buoyancy and Newton's Third Law. There's probably something on google or mythbusters about it if you really want to get involved, but it'll probably take a bit more than skimming Wiki.
  • ED209 15 Oct 2013 23:44:06 505 posts
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    @meme But surely the odds of holding the winning (or at least highest remaining) box are, without exception, one out of however many boxes are left? There's no statistical benefit or increased likelihood from doing a certain something from any part of the game. It's entirely based around drama and faux-tension.

    Samantha Janus?

  • Deleted user 16 October 2013 00:33:50
    @meme

    I agree with your answer, but I have two other questions that are altering my reasoning of the explanation:

    1. Does the configuration of the (nylon) pingpong ball in water (ionic solution) and steel ball in water produce a weak capacitor? (eg more potential on the right handside)

    Edit2: I'll get my wording right eventually

    2. Is it easier to stand at the edge of a swimming pool and hold someone from sinking to the bottom, than holding someone dangling over a ledge? And if so, then would that suggest the steel ball has a force (from the water) acting upwards, partially against gravity? And then by Newton's 3rd law of motion should the righthand beaker/plate experience a downward force of equal and opposite magnitude?

    And just for fun, if the temperature was assumed different to room temperature, would the expected result change?

    Edited by vizzini at 00:47:12 16-10-2013
  • President_Weasel 16 Oct 2013 00:53:01 9,134 posts
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    The steel ball is hanging from a string and therefore its weight is not affecting the scales at all.
    The ping pong ball and the air therein weigh something, however little. Therefore the left side will drop.
  • President_Weasel 16 Oct 2013 01:02:18 9,134 posts
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    Aw shite, some of the weight of the steel ball will be supported by the water, and only the majority of it will be supported by the string. So the actual answer is: intriguing experiment, get me a balance, two beakers, some string, a ping pong ball and steel ball of equivalent volume, a clamp stand, some students, and a postgrad to run the experiment while I film it.
    And some video equipment.
    And a lab.
  • Deleted user 16 October 2013 02:16:13
    President_Weasel wrote:
    Aw shite, some of the weight of the steel ball will be supported by the water, and only the majority of it will be supported by the string.
    Basically, yeah, although I can't be arsed to actually work out the exact ratio of forces (though I have a feeling it's actually majority on the water side of things). It's kind of but not really the same sort of thing as "do flying birds in a closed cargo container increase its weight". Which they do. The trick with these sorts of things is to think in terms of forces, rather than masses.

    This kind of helps visualise it - http://fsuguide.weebly.com/suspended-steel-ball.html - by Newton's Third Law, if the reading of the scale is less than the weight of the ball, that remaining force is being applied to the water. And if you really care about the maths behind it, there's stuff about it in method two here - http://www.physics.arizona.edu/physics/gdresources/documents/13_Archimedes.pdf
  • Deleted user 16 October 2013 06:59:52
    Saying the pingpong ball will "pull up" that side is a bit like suggesting you can pick yourself up , no?
  • Destria 16 Oct 2013 07:14:20 2,823 posts
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    Yeah. What if the pingpong ball was just floating on the top of it? It'd be only the weight of the ball that affected that side.

    Buoyancy "push" of water against ping-pong ball is counterbalanced by the upward "pull" of the ping-pong ball against the beaker, so it balances.

    Buoyancy "push" of water against steel ball doesn't get counterbalanced by anything, so right side is "pushed" down.
  • Fake_Blood 16 Oct 2013 07:31:02 4,145 posts
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    The ping pong ball pulls on the bottom of the left beaker, it changes nothing to the weight of that side. The balance stays level.
  • Tonka 16 Oct 2013 07:35:13 20,151 posts
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    Why aren't there readily available answers t these things? We'll have to wait for kxcd to make a comic about it I guess.

    If you can read this you really need to fiddle with your forum settings.

  • Mola_Ram 16 Oct 2013 07:54:54 7,145 posts
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    It would stay the same, because if you put an aeroplane on a treadmill, it is going really fast while also not moving
  • Tonka 16 Oct 2013 08:18:49 20,151 posts
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    The force of the wheel actually pushes the treadmill beyond its limits so it will break and then take off. Leaving the plane on the ground in a sorry state.

    If you can read this you really need to fiddle with your forum settings.

  • sickpuppysoftware 16 Oct 2013 09:10:07 1,322 posts
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    Which ball always tells the truth and which always lies?

    You cannot stop me with paramecium alone!

  • LeoliansBro 16 Oct 2013 09:24:35 43,641 posts
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    None of the weight of the steel ball is being supported by the water, unless the steel ball is itself right at the bottom and the string is slack. If the string is in tension, then it is doing all the work and can be ignored, hence the ping pong side goes down.

    LB, you really are a massive geek.

  • Destria 16 Oct 2013 09:38:04 2,823 posts
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    The string supporting the steel ball won't be doing all the work if the steel ball is submerged. Heavy items are easier to lift underwater than out of water, as the buoyancy effect of water provides some lift.

    Archimedes principle! "Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object."
  • LeoliansBro 16 Oct 2013 09:44:11 43,641 posts
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    You misunderstand Archimedes, the steel ball isn't being held in place by the water at all, as if the string was removed it would sink to the bottom (and would do so in any volume of water).

    The steel ball and string is outside of the experiment. The buoyancy on the other side is a red herring as it doesn't make that side any lighter, you don't even need the string (which is just there to create the impression of an upwards force).

    I still say the left side goes down.

    LB, you really are a massive geek.

  • Megapocalypse 16 Oct 2013 09:53:52 5,372 posts
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    If you remove one of the balls does it increase the chance of the treadmill taking off?
  • glaeken 16 Oct 2013 09:53:53 11,133 posts
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    As far as I can see one side has something additional which is the ping pong ball side due to the ping pong ball being connected to the jug. The steel ball is not part of the system. The displacement of water is the same for both sides so surely that cancels out not that I see the displacement as meaning anything anyway as the water is not going anywhere it's just displaced.

    So the left goes down to me.

    I look forward to finding out why I am wrong.

    Edited by glaeken at 09:54:47 16-10-2013
  • Destria 16 Oct 2013 09:57:01 2,823 posts
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    That's what Wikipedia says about Archimedes. Water exerts a buoyancy force on any object that displaces it, equal to the weight of the water it displaced.

    It would sink, but it'd exert a smaller gravitational force downwards. Hence humans appear to weigh less in water. Water exerts a buoyancy force on any object that displaces it... if it's enough of a force to counteract the gravitational pull on the object (namely if the mass of the object is less than the mass of the water it's displacing), then it'll float. If it's exactly the same, then it'll effectively be suspended in water. Otherwise it'll sink.

    First thing I'm going to do is go home, put a big bowl of water on some scales, and ram my fist into it. See what happens. Because I'm not convincing myself
  • LeoliansBro 16 Oct 2013 10:34:57 43,641 posts
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    Buoyancy is a complete red herring.The steel ball exerts no force downwards because it is suspended on a string outside the experiment. If I dangle a steel ball in my bathtub full of water it doesn't make the bathtub full of water heavier.

    The string holding the ping pong ball is similarly irrelevant, it just makes it look like there might be something pushing the left side up.

    LB, you really are a massive geek.

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