Why is the reaction force in this direction?

[Neon32]

I want to understand why the reaction force of the short cable and link cable is in this direction? I want to understand it instead of memorizing. Your help would be much appreciated. Thanks in advance!

 

[Bystander]

"Why?" Consider the resultant(s) for other directions.

 

[jack action]

From the point of view of the bar, something (the rope or link) is pulling it in that direction.

If you would analyze it from the rope or link point of view, the bar would be pulling on it and, thus, the direction would be in reverse.

Imagine yourself in tug of war, Who is pulling on the rope? From each team's point of view, it is the other team.

 

[CWatters]

It's easy to understand the case with a rope... It can only provide a force in the same direction as the rope. It's less obvious with the short link but the answer is the pins at the end. Because both ends have pins the link cannot transmit a force in any other direction.

 

[Randy Beikmann]

Neon32, it should help to take moments about one of the two ends, which are both pinned. The resultant moment must be zero, and that requires a certain ratio of the force components along the coordinate axes (Fx/Fy). That determines the direction of the resultant force.