Thread: Up Side Down Pool

Okay, i dont know if this is the right secion or not but ive had an idea for a while now.

When you put a straw in a glass of water and put your finger over the top it causes a vuccum and the water stays in the straw when you take the straw out of the glass. Well if you made a giant straw, dropped it in, say the ocean, covered it and pulled it out would the water still stay inside? When i say giant straw i mean huge, wide enough to swim in. (I wanna swim upside down)

...just because the water isn't falling doesn't mean you wouldn't fall...

and would the water fall once the surface tension was broken?

The answer is no. Anything much bigger than a straw, and the air gets up in around it and the column of water falls out. Try it yourself with a cup or something about that diameter.

Originally Posted by Chemboy

...just because the water isn't falling doesn't mean you wouldn't fall...

and would the water fall once the surface tension was broken?

When you are in a pool do you automatically sink to the bottom? no
and when the surface tension of water in a straw is broken the volume of whatever is displacing the water is how much water comes out.

The answer is no. Anything much bigger than a straw, and the air gets up in around it and the column of water falls out. Try it yourself with a cup or something about that diameter.

I know a cup wont work but i thought that was because of its width compared to its height. A straw is very skinny and very tall, a cup isnt. If it were proportional to a straw it wouldnt work?

Originally Posted by mvm2691

I know a cup wont work but i thought that was because of its width compared to its height. A straw is very skinny and very tall, a cup isnt. If it were proportional to a straw it wouldnt work?

Orginal hypothesis, but no, the length to width ratio won't help you. A very small cup, the diameter of your straw, would hold water in when turned upside down. A very big straw won't.

If anything, it's the ratio between the diameter of the opening and the diameter of the water molecule that matters.

Just like you can splash water onto the ceiling and some drops will stay there, smiling at you like short oval-shaped stalactites, but those drops will be limited in size. There is no way - in normal earthly gravity and atmosphere - that you could make such a hanging drop the size of your fist. And certainly not enough to go swimming in it.

Sorry to disappoint you. But the world still is a fascinating place, even if tne nearest upside-down swimming pool is in Australia.

Agreed. Try it with a piece of pipe. (Just don't let the suction hurt your hand. It can get fairly strong until the other end of the pipe leaves the water.)

A more interesting idea is the use super-powerful vortices of air to suspend a large sphere of water in mid-air. (Imagine those demonstrations with a beach ball at the local science museum.) Good luck on getting it to actually work though.

You could rotate an enormous bowl of water. Then at the rim you'd have vertical water for swimming... or surfing! :-D

There are telescope mirrors like that. They have a liquid mercury surface.


Get enough water into space, dream come true. Waves in a Large Free Sphere of Water

Originally Posted by MagiMaster

A more interesting idea is the use super-powerful vortices of air to suspend a large sphere of water in mid-air. (Imagine those demonstrations with a beach ball at the local science museum.) Good luck on getting it to actually work though.

You are on the brink of inventing an airbrush!

Capillarity holds the fluid in the straw.

We used to use a callowasa to get samples of chemicals out of 55 gallon drums. It does leak out but it takes a while.

COLIWASA Composite Liquid Waste Sampler

We used to use PVC or glass coliwas's for acids. And zinc plated, EMT (electrical metalic tubing), for, aromatic hydrocarbons.

A driver I worked with, told me about an accident at a wrapping paper company that prints wrapping paper for the large retail stores in our area. Custom wrapping paper for Bloomingdales and other large stores.

They make the glossy painted paper that you see on expensively wrapped presents.

They use nitric acid and other acids in the plant. One fellow stuck a zinc plated coliwasa into what he believed was a drum of aromatic hydrocarbons. And the drum literally blew up, with a violent chemical reaction. Someone had poured aromatic hydrocarbons in the drum of acid. The aromatic hydrocarbons went to the surface and it appeared to be something other then acid.


Sincerely,


William McCormick

I just realized that you remind me a lot of Professor A.A. Dinwiddie.

Because of the properties of capillary action, the amount of water that will rise up a straw is inversely proportional to the radius of the straw. So the bigger the straw the less water that will rise up in it. For a straw big enough for an average human to fit into it would need about a 75cm radius, with that only about .019mm. It would be rather hard to swim in that amount of water I would think.

Also, even if you did find some way of getting enough water up a tube, once you broke the surface tension all the water would then leave the tube. It would not just displace the amount of volume that you take up as mentioned earlier.

Another interesting thing with this is that if you are less dense than water you would be pulled upward which would just in a sense bring you deeper into the water. I'm all for doing some upside down swimming if you can figure out how to do it though!

Originally Posted by HarryPotter

Another interesting thing with this is that if you are less dense than water you would be pulled upward which would just in a sense bring you deeper into the water.

You can see this happen to a smaller object. Use an empty perfume bottle (very narrow neck), fill it with water, turn it upside down and push a matchstick into it.

The reason the water stays in the straw is because its weight is supported by the force due the atmospheric pressure.

Suppose your straw has uniform cross-sectional area If is atmospheric pressure, then the force supporting the column of water is

Let be the height of water in the straw. The volume of water in the straw is if is the density of water, then the mass of water in the straw is and its weight is

So, in order for the water to stay in the straw, you need to have

• 

Now plug in these values:

approximately.

Hence the height of the water in your straw cannot exceed about 10.34 metres (assuming your giant straw is that long) at sea level. For seawater, this maximum height will be less as seawater is denser than ordinary water.

Perhsps surprisingly, the maximum height of water you can pick up in your straw does not depend on the cross-sectional area of the straw. However, the bigger the cross-sectional area, the harder it will be to keep air from seeping in through the sides of the straw and causing the mass of water to fall off. Hence the maximum amount of seawater you can pick up in your giant straw will always be limited (both theoretically and physically).

maybe ill just dump a bunch of water into space and swim upside down there :wink:

thanks tho guys

Originally Posted by MagiMaster

I just realized that you remind me a lot of Professor A.A. Dinwiddie.

He must be a great individual. Ha-ha.


Sincerely,


William McCormick

Originally Posted by JaneBennet

The reason the water stays in the straw is because its weight is supported by the force due the atmospheric pressure.

Suppose your straw has uniform cross-sectional area If is atmospheric pressure, then the force supporting the column of water is

Let be the height of water in the straw. The volume of water in the straw is if is the density of water, then the mass of water in the straw is and its weight is

So, in order for the water to stay in the straw, you need to have

• 

Now plug in these values:

approximately.

Hence the height of the water in your straw cannot exceed about 10.34 metres (assuming your giant straw is that long) at sea level. For seawater, this maximum height will be less as seawater is denser than ordinary water.

Perhsps surprisingly, the maximum height of water you can pick up in your straw does not depend on the cross-sectional area of the straw. However, the bigger the cross-sectional area, the harder it will be to keep air from seeping in through the sides of the straw and causing the mass of water to fall off. Hence the maximum amount of seawater you can pick up in your giant straw will always be limited (both theoretically and physically).

I have never tried it to that distance with a small tube. However I have noticed that water will not even drop out of a small tube, that is ten feet long. I suspect that a very small tube will lift water much higher then 33.34 meters.

If I get a chance I will check it out. I would think that a very small tube will lift a tremendous height of water. Effortlessly. Like trees do.

Trees lift water through three methods. Capillarity, osmosis, and evaporation. Allowing water to be carried up a tree, 70 feet or more. I believe that capillarity plays a big part in making the water almost weightless in the very fine tubes that supply water to the tree.

Sincerely,


William McCormick

The bubble inside a bubble of water in microgravity makes me think of putting a giant sphere of water in space with a giant sphere of breathable air inside with a boat or floating city or something inside that.