# Is it really possible for water to be held in a “cone shape” for a brief period of time?

I just saw this "trick" where a cup of water is turned over onto a table without spilling (using a piece of cardboard. After removing the cardboard from underneath the cup, the person then removes the cup in a particular way (lifts straight up and twists) and lo and behold, the water stays in it's position as if the cup were still there!? (watch the video to fully understand) Is this really possible? If so, and the real question I'm looking to have answered is, how?

After further research it appears that deionized water is needed as well.

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Let's split up the forces, it gives an easier view on what should happen.

## Horizontal Forces

What we see is a centrifugal force.

Centrifugal force (from Latin centrum, meaning "center", and fugere, meaning "to flee") represents the effects of inertia that arise in connection with rotation which are experienced as an outward force away from the center of rotation

So, outward force away from the center of rotation. This means that the water would only be able to appear in place if there is a force in the opposite direction, which is known as friction. Where is the friction if you take the glass away? There is no friction anymore, thus that video shows special effects. ;-)

## Vertical Forces

There's also the gravitational force. What would keep the water up so long? Nothing.

Furthermore, if you look at his other videos, you can confirm it's CGI... :-)

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So in otherwords... I've been duped. – KronoS Feb 24 '11 at 21:44
The guy's good tho with the CG. Probably had a second tinted glass cup that was pulled up. – Genie Feb 25 '11 at 3:31
I'm not so satisfied with this explanation; is friction the only thing that can keep water from moving outwards? Also, your explanation of gravitational forces doesn't make too much sense; I can pile a bunch of blocks on top of each other and claim that I am defying gravity by the same token. Perhaps there are forces at play that you don't know about? Maybe you could address all of the possible kinematic, intermolecular, and quantum forces that are at play and show why they aren't enough to counter the center-fleeing and downward-seeking forces you listed. – Justin L. Feb 25 '11 at 5:46
In my oppinion there is almost 0 probability that it is CGI (Computer Graphics Image). The software to make a model of a static glass of water with proper caustics is commom and realistic. But to simulate the rotating water, AFAIK, there is none available to the public. It has to be a renderer and a fluid physics simulation. The option of composing frame by frame means a lot of work to keep the continuity of the rotational motion. – Helder Velez Feb 25 '11 at 9:35
Feel free to correct my answer, I'm not a Physics Expert but those are just my thought of why it would be impossible. – Tom Wijsman Feb 26 '11 at 21:12

The spinning action he imparts is not enough to set the entire mass of water spinning for a start. Due to frictional forces within the static fluid mass, it would take considerably more time to set the entire mass into motion than his quick twisting action. Water is a fluid, not a solid as some misinformed poster stated in reference to using bricks. Solids can hold shape as they are just that, a solid. Ice will hold shape too; you can stack ice but you can't stack water.

Gravity will force the collapse of the water column as soon as the glass is no longer supporting it. There is also the issue of the water adhering to the glass surface due to surface tension effects. This is just trickery with CGI, and yes there are CGI tools available to the public for doing these slick effects.

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No, It was CG. The video-maker himself said it. Here: http://forums.cgsociety.org/archive/index.php/t-957350.html

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We used to do the trick with the glass of water and a piece of paper when I was a child. You fill the glass, to the rim it is more successful, cover with a dry piece of paper or a bit of flat aluminum foil, put your hand flat over it, and upend it slowly. Slowly remove the hand. The water does not empty. The paper stays. The weight of the water is balanced by the ambient pressure and the suction that occurs at the top, as gravity pulls the water down and a vacuum is formed at the top of the glass.

At first glance I thought that conservation of the angular momentum given by the twist, same with a spinning top, would keep the water there ( it looks as if it is spinning in the video). But the suction from the removal of the glass (goes plop, I am an experimentalist after all) could not produce such an unperturbed shape, imho. So I vote that it is a trick, although the way the water collapses without any debris of bags is realistic, so there must be video manipulation too.

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Its a trick. There are 2 vessels:

the outer that we saw, and an inner one, transparent and soft. Stopt it at 1:48 you will see the water move out from the bottom. Under atmospheric pression the vessel merge down. The image after this moment is truncated and we can not see the remnants in the table. The water was previously set in rotational motion (before the image restarts after those words).