Why wouldn't this space propulsion work?

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Discussion Overview

The discussion centers around the feasibility of a proposed space propulsion system, with participants questioning its ability to generate forward motion. The scope includes theoretical considerations of propulsion mechanics and the principles of physics that govern motion and forces.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants question the mechanics of the proposed propulsion system, asking for clarification on how it could achieve forward motion.
  • There are inquiries about the work done in the system, particularly regarding the forces involved when the weights are repelled by the electromagnet and their subsequent motion.
  • One participant argues that the weights would retain momentum and that less force would be expended in the return direction compared to the initial push.
  • Another participant suggests that the rearward force exerted by the ball upon contact with the bend compensates for forces not accounted for in the initial diagram.
  • A warning is issued regarding the classification of the device as a perpetual motion machine, which is generally not permitted in the forum discussions.

Areas of Agreement / Disagreement

Participants express differing views on the viability of the propulsion concept, with no consensus reached on whether it could work or why it would fail. The discussion remains unresolved regarding the mechanics and implications of the proposed design.

Contextual Notes

There are references to principles of conservation of momentum and energy, with some participants indicating that the design may violate these principles. The discussion highlights the complexity of the mechanics involved, but does not resolve the underlying assumptions or calculations.

Who May Find This Useful

Individuals interested in propulsion systems, physics principles related to motion, and the theoretical limits of mechanical designs may find this discussion relevant.

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.
 
Last edited:

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