Measuring Gravity in Your Basement

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

Comments

Other fun experiments to try

[QuantumG]

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.

6.67259

[CyberDruid]

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).

Sensitive

[vossman77]

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

Re:Sensitive

[bcrowell]

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...