Combining two different internet debates

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Speedy thing goes in, speedy thing comes out
E: I was just quoting GladOS..... Not really thinking about the actual physics!
- Yeah but the thing isn't moving the portal is, and the energy has to come from somewhere if the portal makes the thing go fast.
  
  The energy would come from the trolley. The people would launch out at approximately the same speed as the trolley interacts with them and the trolley would slow down in response to how much kinetic energy was transferred to the people.
  
  This is correct. The motion of the people is relative to the Portal. It doesn't matter if the trolley is accelerating the Portal towards them or something is accelerating them towards the Portal. Therefore they accelerate out of the other side with some retained momentum. Technically it probably resembles something in between pictures A and B.
  This reminds me of the experiment about whether an airplane could take off from a treadmill.
  
  Only if you assume the people will experience friction against the portal.
  If they would accelerate to the speed of the train within the time it takes them to go through it, they'd experience very high pressure change against the due to one part of body accelerating faster than the other. This would cause the bodies to explode out the portal
  
  Interesting. It would be the same as if the trolley hit them directly.
  
  Yes, as I noted elsewhere in the thread, the part of the body exiting the portal will experience inertia as it enters into the space outside the second portal and it will be forcefully pushed by the next part of the body heading into the first portal and thus imparting momentum to the parts ahead.
  If this momentum has to be taken from anywhere its from the portal itself and by extension the train.
  
  Now you're thinking with ~~portals~~ physics!
  
  The energy would come from the trolley.
  Has the trolley come to a complete halt, or even showed down? If not, then either no energy has been transferred to the people and they just flop out, or we've just invented perpetual motion.
  
  This guy is thinking with portals!
- No moving objects are entering.. lol
  
  Then they can't enter at all and have to be flattened by the portal, because they must have motion too exit the other portal

310 comments