4 ms·

Low pressure, vacuum, I doubt physics care (not a physicist), it's just a pressure differential, just a bigger or smaller one. So the effects would just be smal

Low pressure, vacuum, I doubt physics care (not a physicist), it's just a pressure differential, just a bigger or smaller one. So the effects would just be smaller.

wtvanhest 10y ago
Right, but using a true vacuum as your comparable for the construction of a partial vacuum is nonsensical. This structure has a differential closer to an airline, not a space shuttle. Airplanes can handle that pressure differential with a thin layer of aluminum. They can even have windows! Thinking through this a little more. In basic terms, you just need a tunnel big enough combined with low enough pressure that at speed, the train has significantly less air to push out of the way. I'm sure it is some complex math, but someone who understands the math could figure it out.
- deleted 10y ago
  [deleted]
- danbruc 10y ago
  The air pressure 10 km above sea level is about 25 % of the air pressure at sea level, the Hyperloop paper says the air pressure in the tube will be 0.1 % of the air pressure at sea level. So the pressure is way closer to a perfect vacuum than to the air pressure outside of airplanes.
  - stouset 10y ago
    It's still a linear change. The tube needs to withstand 1 ATM of pressure, which isn't all that much in the grand scheme of things.
    - danbruc 10y ago
      Withstanding one atmosphere is certainly not an unsurmountable challenge but given the dimensions and given that this thing is supposed to be cheap it is also certainly not a negligible issue. You also have to maintain the quality of the vacuum, possibly in presence of expansion joints, and you have to deal with the consequences of a loss of vacuum for whatever reasons.
    - jessriedel 10y ago
      Yes, the mechanical forces involved with a 0.75 ATM differential are very similar to a 1 ATM differential. But the same isn't true for leaks and residual gas because the difficulty isn't linear. Pushing a vacuum 0.1 ATM to 0.01 ATM is much harder than from 0.51 ATM to 0.501 ATM.
GarrisonPrime 10y ago
Even a small pressure differential might be a huge boost. At least from what I've seen in my basic physics lab, you don't have to get anywhere near a vacuum or even what most people would call "low pressure" for it to make a significant difference. Just running a tube between two cities of different elevation might allow for zero energy transport of small pods.

Low pressure, vacuum, I doubt physics care (not a physicist), it's just a pressure differential, just a bigger or smaller one. So the effects would just be smaller.

wtvanhest 10y ago

Right, but using a true vacuum as your comparable for the construction of a partial vacuum is nonsensical. This structure has a differential closer to an airline, not a space shuttle. Airplanes can handle that pressure differential with a thin layer of aluminum. They can even have windows! Thinking through this a little more. In basic terms, you just need a tunnel big enough combined with low enough pressure that at speed, the train has significantly less air to push out of the way. I'm sure it is some complex math, but someone who understands the math could figure it out.

deleted 10y ago
[deleted]
danbruc 10y ago
The air pressure 10 km above sea level is about 25 % of the air pressure at sea level, the Hyperloop paper says the air pressure in the tube will be 0.1 % of the air pressure at sea level. So the pressure is way closer to a perfect vacuum than to the air pressure outside of airplanes.
- stouset 10y ago
  It's still a linear change. The tube needs to withstand 1 ATM of pressure, which isn't all that much in the grand scheme of things.
  - danbruc 10y ago
    Withstanding one atmosphere is certainly not an unsurmountable challenge but given the dimensions and given that this thing is supposed to be cheap it is also certainly not a negligible issue. You also have to maintain the quality of the vacuum, possibly in presence of expansion joints, and you have to deal with the consequences of a loss of vacuum for whatever reasons.
  - jessriedel 10y ago
    Yes, the mechanical forces involved with a 0.75 ATM differential are very similar to a 1 ATM differential. But the same isn't true for leaks and residual gas because the difficulty isn't linear. Pushing a vacuum 0.1 ATM to 0.01 ATM is much harder than from 0.51 ATM to 0.501 ATM.

GarrisonPrime 10y ago

Even a small pressure differential might be a huge boost. At least from what I've seen in my basic physics lab, you don't have to get anywhere near a vacuum or even what most people would call "low pressure" for it to make a significant difference. Just running a tube between two cities of different elevation might allow for zero energy transport of small pods.