# the torsion balance of the Cavendish experiment

I need to perform the Cavendish experiment and build a torsion balance but I can't find metallic spheres with enought mass so I was thinking about using a pair of dumbbells instead. My question is if that would be convinient because of the lack of symmetry and what changes would I need to use for the calculations

• You can use whatever heavy masses you can find, it won't matter much. Unlike Cavendish you you have access to a supercomputer and you know how to calculate the gravitational potential of an arbitrary body, so it really doesn't matter much what shapes you are using, if you happen to have two lead Mickey Mouse figurines, the better, that might get you into the Guinness Book. The original experimental challenges will remain, though. You will needs excellent control over the properties of your wire and perform the experiment in a place with minimal thermal disturbance and air flow. Commented Jun 5, 2015 at 14:47
• I'm trying to come up with an experiment I've done where lack of symmetry would turn out to be convenient. Usually symmetry make life much easier! Commented Jun 5, 2015 at 15:10
• @JonCuster: There are particle physics experiments that only work with asymmetric momentum (beam-fixed target or beam-beam collisions with two different beam energies) because we want the collision products to have significant momentum themselves, when they hit the detectors. Admittedly, when we need the highest center of mass energy, like at the typical LHC proton run, then we are back to a symmetric setup. Commented Jun 5, 2015 at 17:14
• @CuriousOne: Fair point, and one even needs to take it in to account at more 'normal' (at least for me) particle energies such as various nuclear reactions like $^{15}$N(p,$\alpha$)$^{12}$C used in ion beam analysis. There the energies required on the accelerated particle are very different between using protons to measure $^{15}$N vs $^{15}$N to measure hydrogen. But, in the center of mass it is all symmetric and in that frame it doesn't matter what you throw at what... Commented Jun 5, 2015 at 17:23
• @JonCuster: Of course, to nature it's all the same, it's just the experimental sensitivity that can be improved by working outside of the center of mass system. I think it's also true that most experimental techniques that try to reduce errors and sensitivity to environmental effects try to maximize the symmetry in one way or another. Certainly in electrical measurements it always pays to "chop" since it greatly suppresses offsets, thermal voltages etc.. The same principle applies to almost all experiments. "Symmetrizing the environment" removes even order errors, after all. Commented Jun 5, 2015 at 17:30