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A vacuum only weighs 1.28 grams less per litre than air. Since there are 1000 litres in a cubic meter, a 3x3x3 meter cube (approximation of a cross section of a
by redwood 14y ago
A vacuum only weighs 1.28 grams less per litre than air. Since there are 1000 litres in a cubic meter, a 3x3x3 meter cube (approximation of a cross section of a unit of the tube) would contain 27000 litres whose air would weigh 76 lbs.
In other words you're talking about sinking 3 meters of tube that would weigh 76 fewer pounds than if there were air. This is probably a small effect compared to the weight of the strong metal casing that would need to surround such a vacuum.
So since we can sink normal air-filled subways quite normally (e.g. the BART in San Francisco) this must be a well-established technology.
- crististm 14y agoIt's not about vacuum being weightless. It's about vacuum being an active stress factor for the entire construction. It will _want_ to collapse. It's not sitting there doing nothing.
- redwood 14y agoWell I was responding to a specific poster who focused on a different issue. Steel tubes can easily withstand a vacuum... a round tube is an extremely strong structure. Sure the joints between pieces would be the harder part, especially with earthquakes and the like forcing flexibility.
- gdubs 14y agoWouldn't they put the vacuum tube inside of a slightly larger tube?