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Measuring Gravity in Your Basement

Posted by michael on from the 9.8-m/s^2 dept.

Jack Durian writes "John Walker, the founder of Autodesk/co-author of AutoCAD has some fun playing pretend experimentalist, measuring gravity in his basement."

12 of 37 comments (clear)

  1. Try to use known problems by Monsieur_F · · Score: 2, Funny

    "I would go to the building superintendent and
    offer him a brand-new barometer if he will tell me
    the value of G"

    --
    McCartney fans pay bus tickets. [...] Lennon fans too, with discretion.
    1. Re:Try to use known problems by Caractacus+Potts · · Score: 2

      He would just take it to the top of the building and drop it. Then, if you know the height of the building and the time it takes to hit the ground, you can calculate G.

  2. Unpatriotic by kippy · · Score: 3, Funny

    How could we let a traitor like John Walker tell us how to measure gravity.

    It's unamerican!

    --
    Blaze a trail to the New World
  3. Other fun experiments to try by QuantumG · · Score: 3, Interesting

    Put a ring of optic fibre on one of the arms and pump laser light into it. Measure how long it takes for the arm to respond. Lesson: Mass and Energy bends space time.

    --
    How we know is more important than what we know.
  4. How about... by jo42 · · Score: 2, Funny

    John Walker come up with a device to measure the Density of Larry Elison?

  5. Re:He designed autocad, and it shows by TwP · · Score: 3, Funny

    As for black holes, they have no magnetic fields. It's part of the "hair" that they shed on their formation. The only physical properties they have are angular momentum, mass and charge.

    Ahem ... along with angular momentum, mass, and charge, black holes also have color: black!

    *rimshot*

    Poor QCD humor, but induldge me -- my company is turning into a dot-bomb.

  6. 6.67259 by CyberDruid · · Score: 3, Interesting

    The gravitational constant is an elusive thing. When I studied quantum physics, the lecturer, who was one of the members of the Nobel Prize committee (I live in Sweden), told us that one of the "sure" ways (there are a few grand questions in physics which has this status, others probably include: finding the mass of neutrinos, evidence for the Higg's Boson, the decay time for protons, etc) to get a Nobel Prize is to measure G as exactly as the other physical constants are known (i.e roughly to the same number of significant digits).

    --

    Opinions stated are mine and do not reflect those of the Illuminati

  7. Patent problems by Rick+the+Red · · Score: 2
    Uh, I'm not a lawyer, but I think his apparatus may violate this patent.

    --
    If all this should have a reason, we would be the last to know.
  8. Sensitive by vossman77 · · Score: 3, Interesting
    I had to do this experiment for an undergraduate physics lab.

    I have trouble believing this setup will work, because
    • The experiment is open air and very sensitive to any movement in air flow and also sound. When closing the door to the room, you can consider you're experiment invalid.

    • A camera is nice for measuring position, but it can also be measured directly by passing the metal balls through capacitor like setup creating much more accurate direct measurements.

    • Typical measurements yield numbers off by a factor of two. Making it very hard to get a good result. The current constant was measure very far underground where the mass of the Earth is more accurate. A laser has been typically used in this case, but doesn't use a computer.

    Experiments today are done with a Cavendish apparatus, which very similar to the one shown. Here's a link with some pics.

    This is unreserached thought, so don't come down on me too hard. I am just recalling from my youth

    vossman
    1. Re:Sensitive by bcrowell · · Score: 3, Interesting
      I had some students do experiments using Walker's technique. Some photos are in chapter 10 of this online book. You're right that it's very very touchy, and you're not likely to get more than an order-of-magnitude estimate of G (although an o.o.m. estimate is still interesting). Air currents are a big problem if you're in the room, but once you leave the room, it's not an issue unless the heating vents are open or something. That's the point of using a video camera -- so you can be out of the room. One thing that worries me is that entering the room to insert the masses may cause air currents big enough to disturb the apparatus. We never got good quantitative results.

      Walker is an interesting character. He has some very cool free-as-in-beer server-side astronomy software on his site, although it's a shame it doesn't seem to be open source. But then, this is a guy who helped found Autodesk, which used hardware dongles to prevent copying...

      --
      Find free books.
  9. How the current Big G was measured at Los Alamos by Dave21212 · · Score: 2, Informative



    You want to see what Gabe Luther and and William Towler,current "holders" of Big G, used to measure it ? Here's a great shot of the torsion balance device from this short summary .

    Here's a link to the press room at LANL Look for "17) Measuring the Gravitational Constant ("Big G") -- In the Lab of Gabe Luther, Los Alamos scientist. Sound bite on methodology." - no link but an interesting page of resources.

    --
    "Whoever would overthrow the liberty of a nation must begin by subduing the freeness of speech."--Benjamin Franklin
  10. Re:Nice experiment - but .... by EvanED · · Score: 2, Informative

    The reason he used dynes and stuff (part of the cgs - centemeter, gram, second - system) and not the SI (formerly the mks - meters, kilograms, seconds) system is that most of his measurements would have been different by many orders of magnitude. Who wants to see something with a force of 0.0000001 newtons (kg*m/sec/sec) when you could see 0.01 dynes (gm*cm/sec/sec)?