Undergrad The direction of three forces acting on a line has to be concurrent?

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SUMMARY

The discussion centers on the principle of concurrency in the context of three forces acting on a line. It is established that for a system to be in equilibrium, all three lines of action must intersect at a single point; otherwise, a net torque will occur. The participants reference a "simple" proof from a textbook that supports this conclusion, emphasizing the importance of understanding the geometric relationship between the forces.

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Jason Ko
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I found this theorem in D. Morin's book on mechanics. How to prove it mathematically? Does it have a name?
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Take the point of crossing of two of the force lines of action. If the third line of action does not pass through that crossing, there is a net torque and therefore this cannot happen for a system in equilibrium.
 
Thanks! I was being stupid
 
Jason Ko said:
Thanks! I was being stupid
Probably you didn't read the "simple" proof provided below the statement that you highlighted in the textbook.
 
kuruman said:
Probably you didn't read the "simple" proof provided below the statement that you highlighted in the textbook.
Nor I. Good thing I agree with Morin though … 😛
 
In sci-fi when an author is talking about space travellers or describing the movement of galaxies they will say something like “movement in space only means anything in relation to another object”. Examples of this would be, a space ship moving away from earth at 100 km/s, or 2 galaxies moving towards each other at one light year per century. I think it would make it easier to describe movement in space if we had three axis that we all agree on and we used 0 km/s relative to the speed of...

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