The new "airplane on a treadmill" paradox

shoeless

shoeless

Riffin'
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It will stay in place and the train will hit it - the train moving exerts no forces on it much like if it was in a lift hovering and the lift suddenly fell - it would smash into the ceiling.
 
jbj said:
It will stay in place and the train will hit it - the train moving exerts no forces on it much like if it was in a lift hovering and the lift suddenly fell - it would smash into the ceiling.
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The train exerts forces on the air inside the train, which exerts forces on the helicopter. I think what actually happens depends on how fast the train accelerates, but most likely the helicopter will move backwards in the car a bit (because the air is likely not going to be able to accelerate the helicopter as fast as the train accelerates.

BUT MOST importantly, what kinda asshole flies an RC helicopter on a train? I hope he/she gets lotsa dirty looks from fellow passengers.
 
The air has more mass than the copter, and the air will move backward, pushing the copter forward.

 
...or the copter will move backward with the air. Hmmm. I don't know if the copter is more like the balloon or the pendulum in the video I posted.

But either way, it moves.
 
smurfco said:
...or the copter will move backward with the air. Hmmm. I don't know if the copter is more like the balloon or the pendulum in the video I posted.

But either way, it moves.
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This is exactly correct.
The direction will depend on the difference in mass of the air in the train car and the copter...and there might be some aerodynamics thrown into the equation because the air will move around a copter easier than the balloon.
Actually, the effect on the copter will be a combination of what we saw with the pendulum and the balloon.
That combination existed in both of those scenarios in the video, but one effect overwhelmed the other so as to make one pretty much negligible. He used two extreme examples to demonstrate the point.

But, yeah stuff is going to move around.
 
smurfco said:
...or the copter will move backward with the air. Hmmm. I don't know if the copter is more like the balloon or the pendulum in the video I posted.

But either way, it moves.
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it's more like the pendulum (denser than air)
 
The helicopter tugs your pud, rifles through your baggage, and asks what you had for breakfast. Then it explodes.
 
yabba said:
the information that the helicopter is likely denser than air?
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Yes. I agree with what you are saying because it would be a very safe assumption, but it's still not given information.

and it's hovering. So, it's exerting pressure against air which, in effect, changes it's relationship to air that moves around it (as opposed to it moving through air).
I don't know what exactly the change is, but there's something there.
 
dodgechargerfan said:
Yes. I agree with what you are saying because it would be a very safe assumption, but it's still not given information.

and it's hovering. So, it's exerting pressure against air which, in effect, changes it's relationship to air that moves around it (as opposed to it moving through air).
I don't know what exactly the change is, but there's something there.
Click to expand...
ahh, so maybe this is a lighter-than-air helicopter, and its main rotor is actually used to push it down to keep it hovering.

I think we should also consider that we're making an assumption that the train car is filled with air. It MIGHT be a train car that's been totally evacuated and have no air in it. AND maybe it's in space. (maybe the helicopter rotor isn't spinning (another unsafe assumption on my part!), but it doesn't need to because there's no gravity)
 
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