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comment How is it possible that the energy needed to stop a train is the same as the (chemical) energy in a pack of chocolate cookies?
@John Rennie Turbines are less efficient than multi-stage (3+) reciprocal compounds (which can easily rival any modern diesel when operated properly).
comment Quantum random numbers from a laser — simplest setup?
If you budget is on the order of 2k euro, you can check out those guys: idquantique.com. They make both photon counting integrated RNGs, as well as sell all the necessary components to build one from scratch.
comment When photons reach us, what exactly is happening to us and to that photon?
"Straight line" of a variety you describe has a name to it: en.wikipedia.org/wiki/Geodesic
comment Was Titanic's captain's decision correct?
One additional approach was to try to develop speed astern to slow down the rate of flooding at the bow. Russian destroyer "Sposobnyi" ("Capable") had lost a considerable part of its bow because of mine explosion on 8th of January, 1942 and was able to save itself by giving a full speed astern (hydrodynamic pressure would lift and hold the damaged bow section in the water) and going the whole way to base "aft forward".
comment Do low frequency sounds really carry longer distances?
You're confusing multiple things here (may be split the question in 2?). What you hear sitting near the non-amplified turntable is mostly determined by your ear's sensitivity to various frequencies, not some propagation phenomena (check out the diagram: diracdelta.co.uk/science/source/t/h/threshold%20of%20hearing/…).
comment Reciprocating vs. rotating machines
Specially designed gas turbines can go into millions of RPM, not some measly 80k (same applies to electrical engines, btw). The record for a gas mini-turbine speed is roughly 38,000,000 RPM, achieved by J. W. Beams in 1946.