Understanding Moments: Exploring Equilibrium and Line of Action

[qazxsw11111]

Ok, so for equilibrium (no moment about any point), all the lines of action must pass through a single point right? But what about a plank, balanced at its centre, with forces on both sides of the plank so the forces are in equilibrium, and there is no moments also. But what about the line of action meet at a point thing? This confuses me lol.

 

[Doc Al]

Ok, so for equilibrium (no moment about any point), all the lines of action must pass through a single point right?

Not necessarily. A special case is when the three forces are coplanar and parallel, which applies to your plank example.

 

[sir-pinski]

You are correct that for a system to be in equilibrium, there must be no net moment about any point. This means that the sum of all the clockwise moments must be equal to the sum of all the counterclockwise moments.

In the case of a plank balanced at its center with forces on both sides, the forces may be in equilibrium, but there are still moments acting on the plank. However, these moments cancel each other out, resulting in a net moment of zero. This is why the plank can remain balanced without any external support.

The concept of the line of action is related to the direction of the force and its point of application. The line of action is an imaginary line that passes through the point of application of the force in the direction of the force. In the case of a plank balanced at its center, the lines of action of the forces on either side of the plank intersect at the center of the plank. This means that the forces are acting in opposite directions along the same line of action, resulting in a net moment of zero.

I hope this helps to clarify your confusion. Equilibrium and the line of action are important concepts in understanding how forces act on objects, and it is important to understand their relationship in order to solve problems involving moments and equilibrium. Keep practicing and you will become more comfortable with these concepts.