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From ExtremeTech:
Late yesterday, Elon Musk finally unveiled the Hyperloop: A partially evacuated tube, where pods floating on air bearings and accelerated by linear motors will travel between San Francisco and Los Angeles in under 30 minutes, at around 760 mph - just under the speed of sound. While this sounds exciting, it's important to bear in mind that the Hyperloop - if this hypothetical mode of transport is ever built - serves a very niche need and will probably have almost zero effect on 99% of the world's population.
The Hyperloop is, in essence, an air hockey table with pucks (pods) that are accelerated inside a tube using a technique that's similar to railguns. To reduce air resistance (drag), the air pressure inside the loop is reduced to "1/6 that of the pressure of the atmosphere on Mars," or just 0.1% of Earth's atmosphere, using vacuum pumps. This reduces the drag by 1,000 times, which suddenly makes near-speed-of-sound travel viable. While vacuum pumps are used, and the air is very thin inside the Hyperloop, it's important to note that this isn't really a vacuum tube. The pressure in the tube will be 100 Pa (0.75 torr), while a high vacuum usually has an air pressure of 0.1 Pa or less, and one of the best-known vacuums - outer space - has an air pressure of around 0.0000000001 Pa. It is difficult enough to create a high vacuum in a single room, and it would be prohibitively difficult (and expensive) to produce a 700-mile-long vacuum tube.
Read the whole article
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Re: Hyperloop: Hypothetical Pipe Dream, Or the Most Important Invention Since the Car?
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