Will a Wire Hanger Bowl Hold Water?

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Discussion Overview

The discussion revolves around whether a wire hanger, shaped into a bowl and spun at high speeds, could hold water or solid objects. Participants explore the implications of centrifugal force, gravity, and the mechanics of rotating systems, considering both theoretical and practical aspects of the scenario.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant argues that the wire hanger cannot hold water, comparing it to a bowl with a hole, suggesting that centrifugal force would cause the water to escape.
  • Another participant proposes that the viscosity of water might allow it to stay in place temporarily, depending on the rotational speed and the shape of the wire.
  • A different perspective is introduced, questioning whether the wire could hold solid objects like a tennis ball or ping pong ball, citing the balance of forces involved.
  • One participant explains that the shape of the wire is crucial, noting that a paraboloid shape could theoretically allow an object to rest on it without friction, but instability could arise from small movements.
  • Another participant challenges the idea that a solid object could be held, likening the scenario to a blender and emphasizing the increasing force with higher speeds.
  • There is a clarification request regarding whether a response pertains to the general discussion or a specific post, indicating potential misunderstandings about the stability of objects on the rotating wire.
  • One participant asserts that the stability of an object on the wire is similar to that of an object on a slanted surface, suggesting theoretical possibilities without visualizing blenders or similar devices.

Areas of Agreement / Disagreement

Participants express multiple competing views on whether the wire hanger can hold water or solid objects, with no consensus reached on the matter. The discussion remains unresolved, with differing interpretations of the mechanics involved.

Contextual Notes

Participants reference various forces such as centrifugal force, gravity, and friction, but the discussion does not resolve the assumptions about the shapes or conditions required for stability in the rotating frame.

robstrous
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Me and a friend had an argument. Say you had a wire hanger and bent it into the first shape shown in the attachment (a straight portion and then the rest curved into a half "U"). You attach the straight portion to a machine that rotates the object at a very high speed and creates a bowl shape with the half U portion, as shown in the second half of the picture. The argument is this: could the rotational speed of the hanger be fast enough to hold water, or would it fly upward and out of the created bowl?
 

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It cannot hold the water. What an idea!

Suppose you have an actual bowl spinning but with a hole in it. The water will obviouly come out of this hole due to the centifual force (and gravity). Your roating hanger is nothing but a bowl with a big big hole.
(Or a hole with a broken bowl!)
 
robstrous said:
Me and a friend had an argument. Say you had a wire hanger and bent it into the first shape shown in the attachment (a straight portion and then the rest curved into a half "U"). You attach the straight portion to a machine that rotates the object at a very high speed and creates a bowl shape with the half U portion, as shown in the second half of the picture. The argument is this: could the rotational speed of the hanger be fast enough to hold water, or would it fly upward and out of the created bowl?

A good question! I assume you're thinking the viscosity of the water is large enough to hold it in place till the wire comes around again. You might think of using a rotating shape that has some restorative force (kind of like a propeller blade) since any fluid that "droops" will not be picked up on the next rotation unless you have a fluid much closer to molasses on a cold day.

You might look at common kitchen mixers to see how your idea works. In fact, if you're willing to make a little mess, you can come pretty close to your answer experimentally. Keep up this kind of thinking - this is the kind of strange question Richard Feynman was famous (infamous?) for.
 
other perspective: could this wire-cup hold a tennis ball, or a pingpong ball?
 
It could hold a solid object, due to the balancing of three forces -- gravity, friction and the centrifugal force.

The shape of the bent portion matters very much. The vector sum of the centrifugal force and the weight of the body has to be normal to any rotating surface if the object is to keep still wrt the rotating surface without friction. A paraboloid, the surface of revolution of a parabola about its axis, is just such a surface. So, if the wire were bent in the shape of a parabola, a ball placed properly would rest on it. But if it moves just a bit wrt the rotating frame, the coriolis force would shift it out of equilibrium.

A small drop of water, whose dimensions are smaller than the thickness of the wire, will cohere and be carried along the bent portion of the wireif placed properly. But if the volume is more, the drop will tend to push out around the wire due to centrifugal force.
 
It won't hold a solid object. What you have there is a blender.

What you are suggesting is that if you spin it fast enough, an object won't be able to fall through. The faster it spins, the less an object will be able to drop before hitting it. But then also, the faster it spins, the larger the force when it does hit.
 
Hi Russ,

Before posting a reply, I just wanted to ask you whether your posting is a reply to the general discussion, or to my posting specifically? I have a feeling that what I’ve said could been horribly misunderstood.

After all, it was I who mentioned that it could hold a solid object. The stability of that is exactly the same as keeping an object on a slanted wire on earth. (But theoretically it's possible.) The rest of my writing just describes ordinary mechanics in a rotating frame. Also, in my mind I have no picture of blenders or propellers or the likes.
 
Both. It sounds like youa are talking about an object that is rotating with the wire. That would not be a stable situation because the object would have to be balanced on the wire.
 
Isn't that what I said? I have mentioned all the points you are talking about.
 

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