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by kragen
5814 days ago
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The difficulty with making it larger than nanoscale is that the centripetal acceleration becomes very great, which makes holding a large rotor together tricky; you need very strong materials. Actually, I did the calculations, and for visible light, it isn't even feasible at the nanoscale. The centripetal acceleration of the rim of a rotor of radius r is rω². Rotating at 600THz (i.e. 600 trillion rotations per second), ω = 600T2π/s ≈ 3.8 × 10¹⁵/s. If your radius is 1mm, then your acceleration is about 1.4 × 10²⁷ G. The smallest rotor you can make out of atoms is probably around 0.1nm, which reduces the acceleration to only about 1.4 × 10²⁰ G. If your rotor was, say, an orthohydrogen H₂ molecule, with a distance between the nuclei of about 62pm, and thus a radius of about 31pm, the acceleration is about 4.5 × 10¹⁹ G, which would be a weight of about 74 micrograms pulling on that single covalent bond. The nuclei would be whirling around the covalent electron cloud that bound them together at about 11.7 kilometers per second, and each of them would have about 1.13 × 10⁻¹⁷ J of kinetic energy. Unfortunately, hydrogen's ionization energy is about 2.2 × 10⁻¹⁸ J, so that's about five times as much energy as you'd need to rip the molecule apart. I think. It could work out in the infrared, maybe. You'd just need a way to get the molecule started spinning. So I guess you'd have to make your rotor a lot smaller than a diatomic molecule, or a lot stronger than a mere covalent bond. Generally a 60Hz generator must spin at 360rpm or slower to generate 60Hz. |
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