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| organic god |
 Posted: Wed Apr 30, 2008 12:13 pm Post subject: vacuums |
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Joined: 06 Feb 2008
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can someone explain to me how a vacuum works. i looked on wikipedia and got confused so i came here so someone could give me a basic explanation.
i understand that a vacuum is an abscene of matter. and that there is no such thing as a perfect vacuum.
i was curious as to how one creates a vacuum, and also the applications of it.
did an experiment with my sink where i filled a glass with water, turned it upside down whilst it was in a sin full of water and then pulled it out. i felt resistance as i tried to remove it from the water. is this due to a vacuum.
one final question - how does vacuum suction work, when using a buchner funnel for example, how does running water create a suction mechanism =S.
sorry for the long post
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| William McCormick |
| Posted: Wed Apr 30, 2008 2:35 pm Post subject: Re: vacuums |
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Joined: 03 Apr 2008
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| organic god wrote: |
can someone explain to me how a vacuum works. i looked on wikipedia and got confused so i came here so someone could give me a basic explanation.
i understand that a vacuum is an abscene of matter. and that there is no such thing as a perfect vacuum.
i was curious as to how one creates a vacuum, and also the applications of it.
did an experiment with my sink where i filled a glass with water, turned it upside down whilst it was in a sin full of water and then pulled it out. i felt resistance as i tried to remove it from the water. is this due to a vacuum.
one final question - how does vacuum suction work, when using a buchner funnel for example, how does running water create a suction mechanism =S.
sorry for the long post |
Up until recently the older paint spray guns used vacuum to pull paint from the cup below. By blowing air at a high velocity passed, and around, another orifice, you can create a vacuum in that other orifice. Today many guns are top feed.
When setting up a refrigeration system, you must vacuum out the system, to boil off water and even oil, that is in a system. As well as remove all the ambient air that has gotten into the system while you are piping it.
There are different types of pumps. Some are dry pumps, with graphite veins. Some have other types of fiber reinforced resin based veins that are run wet, in oil. The pump makes a little vapor and some of the vapor is oil.
Some devices that you can connect to a regular air compressor, use the vacuum created by the air pressure, to create an icing effect on one side of the device and a red glowing coil at the other side. All done with air pressure, and a very small air flow. If I get a chance I will find it and film it.
You can never get all the air out of a chamber. The metal walls of the chamber will evaporate into the vacuum, before you get there. But you can remove actually, probably over half of the air in the chamber.
I was watching some high speed video of inert gas in a plasma state. And some of the atoms or molecules of the inert gas, appeared to expand to the size of a very large pin head. That is under ARC conditions, probably the most excited you will get to see atoms here on earth. Yet, in a vacuum I highly doubt the atoms are that expanded.
Most regular vacuums use centrifuge action to pump air. The blades on the centrifuge pumps, spinning pump plate face, are curved to reduce noise and harmonics.
Sincerely,
William McCormick
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| Dishmaster |
| Posted: Wed Apr 30, 2008 3:07 pm Post subject: |
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Maybe I can help. You can imagine the air or any other gas as an entity of small gas particles (atoms or molecules). Depending on the temperature, they move around on random paths. If you put it in a box, these particle hit the walls and produce a force, a thrust, against them. Now, if you have a wall separating two boxes of different pressure (i.e. different number of particles per volume), then the gas with the higher pressure can produce a stronger thrust than the other, just because there are more particles hitting it. This is observed as a force trying to pull something into the gas with a lower pressure. And an extreme low pressure is commonly called vacuum.
Interestingly, you can increase the pressure of the initially low-pressure gas by increasing its temperature. This increases the velocity of the individual particles which in summary leads to a stronger thrust on the wall. |
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| JaneBennet |
| Posted: Wed Apr 30, 2008 5:01 pm Post subject: Re: vacuums |
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| organic god wrote: |
| did an experiment with my sink where i filled a glass with water, turned it upside down whilst it was in a sin full of water and then pulled it out. i felt resistance as i tried to remove it from the water. is this due to a vacuum. |
No, not vacuum. This is due to atmospheric pressure on the surface of the water in the sink. It’s the principle of the Torricelli barometer.
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| SteveF |
| Posted: Wed Apr 30, 2008 7:48 pm Post subject: |
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| Quote: |
| i felt resistance as i tried to remove it from the water. is this due to a vacuum. |
No, not vacuum. This is due to gravity. You'd feel the same 'resistance' even if the container was sealed with a lid. But it is true that the Toricelli principle is what keeps the water in the glass.
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| William McCormick |
| Posted: Wed Apr 30, 2008 8:17 pm Post subject: Re: vacuums |
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| JaneBennet wrote: |
| organic god wrote: |
| did an experiment with my sink where i filled a glass with water, turned it upside down whilst it was in a sin full of water and then pulled it out. i felt resistance as i tried to remove it from the water. is this due to a vacuum. |
No, not vacuum. This is due to atmospheric pressure on the surface of the water in the sink. It’s the principle of the Torricelli barometer. |
Wouldn't the force that held the glass to the water. Be that molecules of water tend to cling to one another. And the force of capillarity. A sudden pull would have to break a lot of bonds of the water, at once to pull away from the surface.
The vacuum in the cup that remains until air is allowed to get into the cup. Is what keeps the water from leaving the cup.
If you move the cup up slowly you can let air get into the cup and it will instantly get lighter.
I tried it, and found that even though the cup is slightly above the surface, the bonds of the water do not let go. And it appears these bonds are what causes the cup to feel heavy, even though it is no longer below the surface.
I also used a cup with a hole in it. And you can just raise it up, if you take your finger off the hole, allow air to get into it.
Would anyone like to hear how ambient radiation would play into this?
Sincerely,
William McCormick
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| JaneBennet |
| Posted: Thu May 01, 2008 1:59 am Post subject: |
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| SteveF wrote: |
| You'd feel the same 'resistance' even if the container was sealed with a lid. |
I doubt it. If the mouth of the glass is sealed, you should be able to lift the glass clean out of the water without resistance.
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| Harold14370 |
| Posted: Thu May 01, 2008 3:14 am Post subject: |
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| JaneBennet wrote: |
| SteveF wrote: |
| You'd feel the same 'resistance' even if the container was sealed with a lid. |
I doubt it. If the mouth of the glass is sealed, you should be able to lift the glass clean out of the water without resistance. |
Well, the resistance is nothing more than the weight of the water in the cup anyway, which is being held up inside the cup by atmospheric pressure. When the cup is lifted out of the water, a bubble of air can now get up into the cup, the pressure on the column of water equalizes, and it falls out of the cup making it lighter.
I think it is best not to think of vacuum as an entity in itself. The forces you sense are just the forces of atmospheric pressure. |
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| sunshinewarrior |
| Posted: Thu May 01, 2008 3:19 am Post subject: |
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| Harold14370 wrote: |
| I think it is best not to think of vacuum as an entity in itself. The forces you sense are just the forces of atmospheric pressure. |
I concur. The notion of a vacuum is a useful concept but beware of reifying it. |
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| JaneBennet |
| Posted: Thu May 01, 2008 3:27 am Post subject: |
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| Harold14370 |
| Posted: Thu May 01, 2008 4:23 am Post subject: |
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| JaneBennet wrote: |
I did not say anything about a vacuum.  |
Right, you didn't. That part of my post was directed at the OP. |
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| JaneBennet |
| Posted: Thu May 01, 2008 4:46 am Post subject: |
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| mitchellmckain |
| Posted: Thu May 01, 2008 7:13 am Post subject: |
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| organic god wrote: |
| did an experiment with my sink where i filled a glass with water, turned it upside down whilst it was in a sin full of water and then pulled it out. i felt resistance as i tried to remove it from the water. is this due to a vacuum. |
I took a second look at what you are describing and the best explanation is just the weight of the glass and the water in the glass which you are lifting is the only downward force your are feeling. The reason that that you feel this downward force increasing is because there is an upward force that is decreasing as you pull the glass out of the water. This is the bouyancy force. For a ping pong ball this force is enough to make the ball float on the water but for the glass that force is still there even if it is not enough to make the glass float.
But if you are asking why the water stays in the cup then you could say that vacuum is an issue. I mean JaneBennet is correct in saying that it is due to the atmospheric pressure which is due to gravity acting on the atmosphere. But on the other hand we could also say this is an issue of gauge pressure and og's experiment creates a negative gauge pressure inside the cup at the top of the water, so you can indeed say that without that negative gauge pressure (or vacuum) there would be no force keeping the water in the glass.
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Last edited by mitchellmckain on Thu May 01, 2008 8:12 am; edited 2 times in total |
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| SteveF |
| Posted: Thu May 01, 2008 7:28 am Post subject: |
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OK, here's a simple and interesting thought experiment on this topic. You have a container filled with water and sealed with a thin paper or plastic lid. The container is inverted over a tank of water so that the lid is slightly below the surface. The container is attached to a spring balance to measure the force/weight needed to support the filled container.
Since the container is sealed, I hope we all agree the the spring balance is measuring only the pull of gravity. There can be no vacuum or atmospheric pressure contributions.
Now the lid is punctured. Atmospheric pressure and/or vacuum can now play a role. Even capillary action and molecular attraction can be invoked if you wish.
Here is your question: would the spring balance measure a difference in force or would it show the same reading as before the puncture?
Greater, lesser, or the same?
(Everyone can play.)
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| mitchellmckain |
| Posted: Thu May 01, 2008 7:51 am Post subject: |
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| SteveF wrote: |
OK, here's a simple and interesting thought experiment on this topic. You have a container filled with water and sealed with a thin paper or plastic lid. The container is inverted over a tank of water so that the lid is slightly below the surface. The container is attached to a spring balance to measure the force/weight needed to support the filled container.
Since the container is sealed, I hope we all agree the the spring balance is measuring only the pull of gravity.
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That's right. Gotcha.
| SteveF wrote: |
There can be no vacuum or atmospheric pressure contributions.
Now the lid is punctured. Atmospheric pressure and/or vacuum can now play a role. Even capillary action and molecular attraction can be invoked if you wish.
Here is your question: would the spring balance measure a difference in force or would it show the same reading as before the puncture?
Greater, lesser, or the same?
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Same of course.
However lowering the whole thing into the water would decrease the spring balance measure because of the increasing bouyancy force upward on the glass.
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