Proving Equilibrium: The Relationship Between Forces and Torque

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    Equilibrium Forces
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Homework Help Overview

The discussion revolves around proving the conditions for equilibrium when three coplanar forces act on an object. The subject area includes concepts of forces and torque in physics.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to understand how to prove that the line of action of three forces must either meet at a point or be parallel for equilibrium. Some participants question the implications of forces being parallel and whether additional conditions are necessary.

Discussion Status

The discussion is active, with participants exploring the relationship between the conditions of forces and the resulting torque. Some guidance has been offered regarding the necessity of forces acting along the same line to avoid rotation.

Contextual Notes

Participants are considering the implications of forces not meeting at a point and the resulting torque that could lead to rotation, indicating a need for clarity on the conditions for equilibrium.

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When three coplanar forces act on an object, and the object is in equilibrium, then the line of action of three forces meet at one point or they are parallel. How can i prove that this is true? Thanks. I really don't know where I should start.
 
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First of all, if you're looking at the case where they are paralell, you need another condition. They need to be parallel and act along the same line, otherwise you have a moment acting on the object, and it causes rotation.
 
Is it because if three forces do not meet at a point, they will produce a torque and cause the object to rotate?
 
Yes, they will. Imagine two parallel forces, let's say at a distance d, of equal magnitude F and opposite direction. Then the equilibrium condition ΣF = 0 is satisfied, but ΣM = 0 not, because you have an unbalanced torque of magnitude F*d.
 

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