Why wouldn't this space propulsion work?

AI Thread Summary
The discussion centers on the feasibility of a proposed spacecraft propulsion system, which relies on the acceleration of weights repelled by electromagnets. Key points include the observation that while the initial push generates acceleration, the system fails to account for the rearward force exerted when the weights contact the bend, disrupting momentum conservation. The concept is closely related to perpetual motion, which is prohibited in the forum, leading to a warning about the topic's viability. Ultimately, the propulsion design does not work due to fundamental principles of physics, particularly conservation of momentum. The thread has been closed for moderation, emphasizing that while the inquiry is valid, it does not align with forum guidelines.
Szkeptik
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Hi!
I'm pretty sure someone would have already made this if it did work, but I don't know why it wouldn't. Can someone explain why this spacecraft couldn't move forward?
 

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Can you explain why you think it would?

Hint:
How much work is done to get the ball to the far end of the tube?
How much work is done to bring it back to its starting point?
(Note, btw, that you have not actually completed a full cycle back to the starting state in your diagram.)
 
DaveC426913 said:
Can you explain why you think it would?
Where are the forces out of balance?

There is acceleration when the weights are first repelled by the elecromagnet and the weights would not lose all their momentum before they reached the other electromagnet on the other end of the tube, meaning that less force would be burned in the other direction that the force that was created by the original "push".
 
Szkeptik said:
There is acceleration when the weights are first repelled by the elecromagnet and the weights would not lose all their momentum before they reached the other electromagnet on the other end of the tube, meaning that less force would be burned in the other direction that the force that was created by the original "push".
The ball, by contacting the bend, will exert a rearward force. This makes up the "missing" force in your diagram.
 
Note that your device is technically a perpetual motion device, which is a forbidden topic here on PF.
It's all right to ask why the design won't work (and there are several PPM principals that describe why), but be warned, this thread probably won't remain open long.
 
Closed pending moderation.

This isn't technically a perpetual motion machine. As described it violates conservation of momentum rather than conservation of energy. However it is close enough that we need to moderate.

EDIT: the thread will remain closed. Dave has identified the reason that it won't work. Working out the details is a good exercise for personal study, but not a good topic for PF.
 
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