# Why do we extend the line of action of a force to meet with another force to have a resultant even if it is outside thw body we are concerned with?

I know that the notion of line of action,point of action and so on are just some hypothetical things which are used to visualize whats going on with some physical phenomenas. So I am basically bragging over something insignificant.

Question: However I am just curious about the problem I am facing regarding this. The problem is that lets say there is a ring having its mass uniformly distributed. Its centre of mass and gravity should be at the centre(of the concentric circles). This ring is hanging in a vertical plane. That means a vetical force is acted upon the ring. It happens to be that the force is distributed in such a way that it looks like the force is acting at the centre rather being acted on the body. But the force isn't acting at the centre though it seems like that. Are we evaluating both perceptions to be true based on the results we are obtaining based on numerous experiments over the same thing and consider this phenomenon to be a law?

Lets take another example. We took a pen and exerted two different force along two different lines of action on the pen and the lines of action of forces aren't parallel to the pen. Those to lines intersect somewhere outside the body of pen. Now if we are to predict its resultant we would just find their resultant considering the two force acting acting at their point of intersection and extend that upto the pen. Now the point at which the resultant intersects with the pen will be considered to be the point of action of the reaultant. But how are we sure about that? The point of intersection of the two lines of incident forces is nowhere on the pen. So apparently isn't this something ambiguous? The incident forces aren't actually acting at the same point but we are considering tgey are doing that but outside the designated body. Are we evaluating this thing based on experimental observations and considering that this is a law that wherever the forces meet won't have any impact on the body we are concerned with as long as the force are acting on the body?

Principle of transmissibility of forces can be relared to this but as far as I know principle of transmissibility of forces is relatable as long as the force is acting on the body and ita line of action is along the body then no matter where we consider the force has acted upon as long as the point of action is considered to be on thw body then the outcome will be same. But my examples aren't about the lines of action being along the body rather just intersects at a point.

• The resultant force "looks like" it is applied to the center of the ring, but it is not. It is just that, a mathematical "illusion", it is not real in any way.
– user65081
Oct 23, 2021 at 22:28
• I know that its something that we consider though it does not happen but what leads us to believe that the illusion perhaps directs us to realistic resultant?
– MSKB
Oct 24, 2021 at 8:26
• I think if you posted pictures of your examples, it'd be better. Mar 17, 2022 at 8:03