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

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In a system in equilibrium, if the third line of action does not intersect the crossing point of two force lines, a net torque is created, which contradicts the conditions for equilibrium. The discussion highlights the importance of understanding the proof provided in the textbook regarding this concept. Participants acknowledge a lack of initial comprehension but express agreement with the established principles. The exchange emphasizes the necessity of careful reading and comprehension in physics discussions. Understanding these fundamental concepts is crucial for grasping equilibrium conditions.
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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 … 😛
 

Thread 'Reference frames, center of rotation, etc'

Topic about reference frames, center of rotation, postion of origin etc Comoving ref. frame is frame that is attached to moving object, does that mean, in that frame translation and rotation of object is zero, because origin and axes(x,y,z) are fixed to object? Is it same if you place origin of frame at object center of mass or at object tail? What type of comoving frame exist? What is lab frame? If we talk about center of rotation do we always need to specified from what frame we observe?
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