From Peter Urben
Elon Musk proposes a Hyperloop transport system to link San Francisco and Los Angeles, carrying passengers inside pods, enclosed within a tube. A fan is to provide air for passengers, and create a compressed-air film beneath the “skis” on which the pods run. This may work in a tube at 0.1 per cent of atmospheric pressure while the carriages are moving (17 August, p 7), but at rest? A fan won’t function in that near-vacuum, and passengers will be starting from rest.
Kenilworth, Warwickshire, UK
