Talk:Magdeburg hemispheres

Comments by Herbee

From other sources I get the impression that von Guericke set up his demonstrations with hemispheres large enough so that the horses could not pull them apart. Detailed information seems hard to find, however. More research required.
—Herbee 00:32, 12 Feb 2005 (UTC)

intellectual property nonsense

The phrase "Magdeburg hemispheres" has been trademarked by Kimball Physics Inc. See http://www.kimphys.com/mcf_vacuum_fittings/Catalog_PDFs/Magdebg_Hemisphere.pdf I hope this doesn't affect the article's status in any way, but I'm still a bit new and I figured I'd note the fact. --Yannick 17:10, 18 Jun 2005 (UTC)

Uh, well I think this is a misunderstanding on their part of the idea of a trademark. No risk here, surely. Theoh 01:44, 12 January 2007 (UTC)[reply]

Unnecessary?

Article: "unnecessary use of two opposing teams of horses"

Only unnecessary if you have an object so immovable that 15 horses can't budge it. I think it'd be easier to find another 15 horses. :-)

Of course, if you could find something strong enough to anchor one side to, it would make the experiment easier, as you wouldn't have the problem of balancing forces: I wonder how they kept the stronger team from pulling the weaker team away (as in tug-of-war). --Slashme 11:59, 6 December 2005 (UTC)[reply]

I thought that it took that many horses to pull the spheres apart. ♫Death gle an er 03:38, 31 August 2008 (UTC)[reply]

I am suspicious of the claim that 15 horses can't lift a small car. They must not have been trying very hard.Eregli bob (talk) 07:20, 5 June 2011 (UTC)[reply]

size

according to the German wikipedia the size of the spheres was about 50cm - that would make them close to two feet. Not really important, but still... --Lamme Goedzak 16:26, 29 June 2007 (UTC)[reply]

Yes, I've found various figures for the diameter: 50 cm (20 in) (1, 2, 3), 56 cm (22 in) 4 5, 6, and 37 cm (14 in) 7. The device in the woodcut looks closer to 2 feet in diameter, for what that's worth. The original hemispheres are still in the Deutches Museum, so it should be possible to get an answer. I want to include an estimate of the force holding the hemispheres together in the article. It's proportional to the square of the diameter, so the factor of 2 spread in values results in a factor of 4 difference in the force. I think I'll change the diameter in the article to the 50 cm figure, the most authoritative sources give that. --Chetvorno^TALK 19:26, 26 June 2008 (UTC)[reply]

A Mistake in the Calculation?

The force holding the hemisphere, as mentioned in the article - 20 kN, seems to miss a 2 factor in the calculation. Notice that in Catala language the number is 40 kN, and I get the same when I try to calculate it. Can anyone confirm it before I edit the topic? Tambah (talk) 14:32, 11 November 2012 (UTC)[reply]

I get 20 kN. The forces on each hemisphere do not add together, they oppose each other and sum to zero net force. If the atmosphere produced a non-zero net force on the sphere, then it would accelerate. This is the same problem that leads people to believe that two teams of horses pulling in opposite directions produces more force than a single team pulling against a fixed object; they don't. I once tried to point that out in the article.--Yannick (talk) 16:54, 11 November 2012 (UTC)[reply]

Well, if you use a fixed object, then both you and the object acts 20kN, so it sums to 40kN. If you use a pulley you can use even less force, but it doesn't change the net force acting on the target. Tambah (talk) 08:25, 12 November 2012 (UTC)[reply]

No. The force X from the fixed object is equal and opposite to the force X from the team of horses, so they sum to 0 kN, provided X<20 kN. If X=20 kN, then the compression force across the seal goes to zero, and air leaks in. In the absence of a pressure differential, the net atmospheric force goes to zero, and the 20kN forces accelerate the hemispheres in opposite directions until the rope tension goes to zero. Pulleys have nothing to do with this.

Anyway, doing our own math is not permitted by Wikipedia policy. Both of our calculations probably exceed WP:CALC and fall under WP:SYNTH. That means you can ask for a citation, and later delete the sentence if no one provides one. I would do the same if you revise the figure to 40 kN. Those spheres in the picture don't look like 50 cm anyway, and the technology of that time wouldn't have come anywhere close to full vacuum.--Yannick (talk) 13:56, 12 November 2012 (UTC)[reply]

You can see it is 20 kN by imagining one hemisphere is anchored to a wall. To pull the other hemisphere off, you have to exert a force on it equal to the force of air pressure on that SINGLE hemisphere, 20 kN. Von Guericke just did it the other way so he could double the number of horses, so it would look more impressive. Two equal teams of horses pulling against each other exert the same amount of force as one team pulling against a stationary post. --Chetvorno^TALK 19:43, 12 November 2012 (UTC)[reply]

The first artificial vacuum had been produced a few years earlier by Evangelista Torricelli?

This is a little misleading. Torricelli had been conducting experiments with suction pumps and was trying to determine what limited their lift height to about 24 feet, so these pumps produced a near vacuum, limited by any leakage and the vapor pressure of the water. OF course, the barometer did have very high degree pf vacuum due to the low vapor pressure of mercury, but Torricelli recognized the space above the mercury column contained essentially nothing.Phmoreno (talk) 17:28, 18 December 2012 (UTC)[reply]

Torricelli and Galileo did not have vacuum pumps. Galileo's initial observations were of large water siphons, and Torricelli produced his vacuum by inverting a glass tube full of mercury. Guericke built the first vacuum pump. So no, you need to do better research.--Yannick (talk) 19:57, 21 December 2012 (UTC)[reply]

Hey, Everyone.

I just wanted to take a moment to stop and say "I love science, and I love Wikipedia." Thank you for all that you do to put this stuff out here for everyone to read and learn. I know that we're all volunteering our time and effort, and I really appreciate it. Even with all of the spammers, vandals, and bots, one page at a time, we're building an amazing compendium of knowledge for the next generations to have and hold in their pockets, and that's just not something that was available to me in my childhood. This give me hope for the future. — Preceding unsigned comment added by 71.236.136.184 (talk) 21:14, 12 September 2013 (UTC)[reply]

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Humpty Dumpty

It is late where I am, but I recall there being an urban legend that the nursery rhyme Humpty Dumpty was inspired by this experiment. This claim is likely false so far as I recall, but despite that, is the urban legend still notable enough to mention in this article? Shmuser (talk) 06:11, 27 September 2016 (UTC)[reply]

With a source, perhaps. A Google books search reveals only "... perhaps from a science experiment... . Interesting, but not very convincing on its own. Any another source? - DVdm (talk) 20:46, 27 September 2016 (UTC)[reply]

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svg

i rebuilt this one: File:Magdeburg Hemispheres sheme.svg --Mrmw (talk) 07:23, 13 May 2020 (UTC)[reply]

"the mercury" — WHAT mercury?

I was reading the article, and I saw the second paragraph begins with this: "Speculation varied about the contents of the sphere. Many thought it was simply empty, while others argued the vacuum contained air or some finer aerial substance drawn from the mercury."

This text was originally added here: https://en.wikipedia.org/w/index.php?title=Magdeburg_hemispheres&oldid=1175989016

"Mercury" isn't referenced anywhere else in the article, and I can't see why it belongs here. I have no idea how it should be corrected. Zgystardst (talk) 17:59, 18 February 2024 (UTC)[reply]

By deletion which I have done. Nick Beeson (talk) 16:00, 21 December 2024 (UTC)[reply]

Draft horses

There is something very wrong here. A draft horse can easily pull 2 kilonewtons all day long. A team of 15 can pull 30 kilonewtons. Actually that is the lowest force that team might exert. Most such teams would have no trouble reaching 45 kilonewtons (3 kilonewtons per horse). This is much more than the 20 kilonewton force holding the spheres together. My thinking is incorrect, or something is amiss here, but I do not know which. For Reference: 15 draft horses experience a force of gravity equal to (approximately) 130 kilonewtons. All they have to do is lean forward, without using their extremely strong leg muscles, and the hemispheres would separate. Nick Beeson (talk) 16:42, 21 December 2024 (UTC)[reply]

Good point. It doesn't seem to say that Guerick used the existing 50 cm hemispheres in his demonstrations with the horse teams. The atmospheric force holding the hemispheres together is proportional to the square of their diameter. By making hemispheres large enough he could make the cohesive force pretty much as great as he wanted. Maybe he had a larger set of hemispheres for the horse team demonstrations? --Chetvorno^TALK 02:18, 22 December 2024 (UTC)[reply]

I calculate that a pair of hemispheres 106 cm (42 in) in diameter, only twice the diameter of the ones in the museum, could withstand 90 kilonewtons, twice the 45 kN you say a team of 15 horses could exert. --Chetvorno^TALK 01:47, 22 December 2024 (UTC)[reply]