I have the elusive dangerous substance in my possession!

Pretty theatrical.

b

Reply to
b
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at on, but still more than I have seen. 66 lbs for us 'merkins.

No he couldn't, unless his mass is less than the 30 kG, which makes him a pretty small guy. He has to displace a volume that has a weight equal to his weight in order to float. jk

Reply to
jk

Actually, he could... Think about a pair of cups/beakers that stack together closely, put a small quantity of liquid in one and put the other one in so the liquid rises to the top of the first one. The "displaced" amount of liquid may be much more than the amount of liquid in the cup.

HTH

Mark Rand RTFM

Reply to
Mark Rand

yep. The OP can do a cheap experiment with two identical disposable plastic cups. A small amount of liquid can support the inner cup with a lot more weight in it. Displacement applies to large bodies of liquid.

i
Reply to
Ignoramus21078

Rubbish! The liquid actually has to be displaced. If there is only 30kg of mercury then it will only keep just less than

30kg off the bottom of the vessel.

Archimedes has been dead for over 2 thousand years and You cannot revise his principle.

-- John G.

Reply to
John G

It is actually an 1880s ships barometer, sorry.

The tube is quite a small bore with thick wall. I have not figured out how to refill it even if I could get the glass sealed and sealed to the top of the mercry resevoir. It seems the mercury was just in the steel (iron) pot but what stops it spilling thru the small breathng hole I have not worked out. I know where ther is an identical one in a museum here in Sydney and I should go and talk to th curator one day.

There are some poor pictures at

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-- John G.

Reply to
John G

I gave you an example of an experiment that would prove the point. Try going into the kitchen and trying it. You may be surprised.

Mark Rand RTFM

Reply to
Mark Rand

The top cup rests on the bottom cup stupid.

Archimedes has been dead for over 2 thousand years and You cannot revise his principle.

-- John G.

Reply to
John G

No, the top cup floats on liquid. Try it.

i
Reply to
Ignoramus12714

Been thinking about this for a while and I think Mark is right. The thing is the "amount displaced" is what would have been present if the level in the outer cup was at the height of the final meniscus. Very good. ...lew...

Reply to
Lew Hartswick

Please explian what makes you think your plastic cup will float any better than any other boat large or small.

-- John G.

Reply to
John G

According to John G :

[ ... ]

[ ... ]

The very atmospheric pressure which you are measuring. The only thing which needs to be sealed is the top of the tube (done by slowly rotating it in a flame until it closes, and then letting it cool slowly, by backing off the flame while you keep rotating it).

The "seal" to the top of the reservoir is only to keep it from rattling. The breathing hole is there to let the atmospheric pressure changes make their way to the top of the mercury reservoir.

You should not need that -- just get some glass tubing from a chem lab supply place, seal it as I described, and fill it with mercury.

It looks like well worth rebuilding.

If the glass is as thick as it appears, you will have to be slow and careful about the sealing of the end of the tube, since the glass will crack if you cool (or heat) it too quickly. And it may be more of a trick finding it. Something closer to heavy gauge capillary tubing, perhaps. :-)

Good Luck, DoN.

Reply to
DoN. Nichols

I quite understand how it all works and even though I am over 70 I can remember a school teacher building a fortin barometer in a science class with just a tube and a beaker of mercury and dipping his finger in the mercury as he inverted the full tube. (All this before the do gooders and workplace safety.)

I have a short glass tube full of mercury in the window so the barometer looks real but is only correct when the pressure is about average. ( I sealed the bottom of the tube myself and it has a plastic stopper at the top.)

I understand the reason for the hole but the one in the museum is lying horizontal in a fitted case seeming to imply it was transported that way and I am not sure if I have all the bits as the person I bought it from did not even know what it was.

One day I will get some better photos and also photograph the works of the banjo barometer which has a tube, a reservoir and a system of pullies and string to transfer the position of a weight floating on the reservoir to the dial on the front.

-- John G.

Reply to
John G

In junior high school we made a barometer out of a milk carton, a metal can that fit inside of the milk carton, some string, a penny, a baloon, a rubber band and a large paper clip. The balloon was stretched over the end of the metal can. The string was attached to the center of the balloon. The can was placed inside of the milk carton with the top cut off. The paper clip was opened up and pushed horizontally though both sides of the milk carton. The string was wrapped around the paper clip several times and the free end attached to the penny. The end of the paper clip was bent at 90 degrees so that as the shaft of the paperclip turned as the balloon moved with changing pressure, the end of the paper clip would rotate in a circle. The thing worked real good once you had it calibrated with the local weather forcast. A piece of paper glued on the side of the milk carton to make a face for the paper clip pointer.

John

Reply to
John

Many (50+) years ago I accumulated a quantity ( ~10 ml) of mercury by dissecting Grand Dad's hearing aid batteries. As far as I know, I am still boringly normal. Gerry :-)} London, Canada

Reply to
Gerald Miller

I am not _revising_ his principle. I do _understand_ his principle. Now, go do the test and stop arguing with the facts.

Mark Rand RTFM

Reply to
Mark Rand

I just did this experiment about a minute ago (not my first time but anyway). About 6 oz of water could rest on appx one ounce of water.

John G is advised to find some disposable cups and try it.

i
Reply to
Ignoramus27175

On Mon, 04 Jun 2007 00:22:04 -0400, with neither quill nor qualm, Gerald Miller quickly quoth:

You mean you're not mad as a hatter, Gerry?

As to normal: if so, what the heck are you doing _here_ on RCM? ;)

--== May The Angst Be With You! ==-- -Yoda, on a bad day --

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Ending Your Web Page Angst.

Reply to
Larry Jaques

Well, I don't have a dog in this fight, and I just did do the test.

Sorry, Mark, you're wrong.

The inner cup is *not* floating. It's resting on the inner walls of the outer cup. Gently grasp the inner cup by its rim and rotate it -- you'll feel the friction between the cups.

The only way your test can be made to "work" is by using two identical cups. If you repeat the test with two vessels of different shapes or sizes, it behaves exactly as Archimedes' Principle predicts. And *that* should tell you that there's another factor involved in your test. That other factor is friction.

Reply to
Doug Miller

What about that extra arm growing out of your back?

Reply to
Michael A. Terrell

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