Jump to content

John Cuthber

Resident Experts
  • Content Count

  • Joined

  • Last visited

  • Days Won


Everything posted by John Cuthber

  1. It might be worth explaining the bizarre unit- the "inch of vacuum". It is, as I said, like trying to describe the thickness of a coin by measuring the difference between that thickness and the width of your thumb. The original idea was fairly simple. You got a mercury filled barometer. http://www-mdp.eng.cam.ac.uk/web/library/enginfo/aerothermal_dvd_only/aero/fprops/statics/node15.html, Then you connected the top of it to your apparatus. The better your pump was, the more it pulled the mercury up. And if your use for a pump was pulling water out of a mine shaft, that's probably as good as it needed to be. You could pull water roughly 13 times further , because it's 13 )or so) times denser than water. The problem is that the pump doesn't pull the mercury up- the atmosphere pushes it up- and the atmosphere is variable.. Well, that's still OK if you need to know if your pump is pulling water out of a mine, because the head of water is also affected by the atmosphere. But, if you want to get a reasonably accurate measurement, you can't use the atmosphere as a reference point. (OK, technically, you can- if you measure it accurately). If the actual atmospheric pressure varies by an inch of mercury, that isn't going to make much difference to the mine pump. A change between 20 inches and 21 isn't worth worrying about. But, if you are actually working with a pressure that's less than an inch of mercury, your "reference" point varies so much that you can't tell if your pressure is positive or negative (well- it' can't really be negative, but that';s what the gauge.would show). None of that will actually help answer the OP's question. Because the question is like saying "my antique clock keeps time to +/- 30 minutes a day. IS that good enough?" Good enough for what? If the OP ever actually tells us what question they want to answer, we might be able to answer it.
  2. Interesting question of definition; does a diamond count as organic, or inorganic? Some definitions include CH bonds... Anyway, I think quartz is probably the commonest inorganic macromolecule. Molybdenum blue is one of the oddest https://pubs.acs.org/doi/pdf/10.1021/ja512758j
  3. And the answer is that it depends what you are trying to do. How did you imagine that we could answer the question without knowing that? It's worse than that. It's like asking how thick a coin is by expressing is as "How much thinner than a thumb is it?". Which part of "impossible" did you not understand?
  4. If the atmospheric pressure is the so called "standard" of 760 mmHg it is impossible to get 30 inches of vacuum.
  5. If you are an insect in the jar it matters very little- you are dead either way. Both are far too low.. If you are trying to do things that need a good vacuum- like build a mass spectrometer, there's no meaningful difference between 29 inches of vacuum and atmospheric pressure. Both are millions of times too high Well, do you now realise that you were wrong?
  6. OK Thredbarron, It's going to work better if you start at the beginning. I doubt that you woke up one morning and thought "Just for kicks, I will hook a vacuum pump and gauge to a jar". What are you trying to do or find out?
  7. I just hope he doesn't smoke. Seriously, the question needs more context. Over what time scale, and what area are you using the alcohol?
  8. We are on a planet made of matter. It is in a universe full (largely) of vacuum. What observations were you hoping to make about the jar that you can't make much more simply about the Earth? Except it's the other way round. This is one reason why inches of vacuum is a stupid unit. He has removed roughy 29/30 of the air. So the pressure is roughly 1/30 *750 mm Hg About 25mmHg Water will boil in that jar at about 27C The other reason why it's a lousy unit is that it literally depends on the weather.
  9. You missed the bit where it took until this week to come up with any sort of controls/ checks at the border. About as US centric as the US. But, by thunder, you have to work at it.
  10. Multiplication is often related to the concept of area. But, in general, it's quite abstract.
  11. I'm sure we all hope that Mr Trump is taking enough of his medication to have a good outcome.
  12. By what? Also, many or most rooms are only about 10- 15 feet across. Again, that's a matter of wealth, not physics. Yep. You will see people wearing it in clinical situations.
  13. You don't need to go to roswell, just a hardware store. Buy a hammer. Lift it up then drop it on a rock. Calculate the power input to the hammer, and the power output delivered to the rock. If you draw a picture it will be more clear what you are wrong about.
  14. If people sneeze at 100 miles per hour then, to make sure that the particles go up not across, you need an upward velocity near 100 MPH You need that all across the room- because you can't be sure where someone will be standing. Such rooms exist...
  15. A commercial manufacturer will grind the mirror until it is "good enough". An amateur will grind it until it is "as good as possible". That's an advantage.
  16. If you buy commercial hydrochloric acid- unless you specify a different concentration- you will get concentrated hydrochloric acid. Other solutions are made by dilution of the acid. The name is not a description of the manufacturing process.
  17. https://en.wikipedia.org/wiki/Repunit
  18. The boy stood on the burning deck whence all but he had fled Twit. Spike Milligan.
  19. I wonder if this discussion has lost focus on the fact that , for much of the world, "air conditioning" means opening the door.
  20. But, it seems, she wanted power more than she wanted to do what was best for the country. So, she went along with Brexit. It's not as if she was a great lover of either justice or the european legal system. https://en.wikipedia.org/wiki/Othman_(Abu_Qatada)_v_United_Kingdom
  21. War as a side track from battle... A comparison between Mrs May's xenophobia which caused problems when she was in office and her denouncement of it now. That principle caused major problems when she was in office.
  22. In exactly which battles is nationalism an ally? (note, it's "the enemy"'s nationalism that starts the unnecessary battle in the first place.)
  23. Yes and no. As soon as anyone walks on it the surface will get scuffed and look bad,
  24. Outstanding hypocrisy from Mrs May to say "Nationalism is no ally in this battle without borders" having been the architect of stirring up racism https://en.wikipedia.org/wiki/Home_Office_hostile_environment_policy
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.