Free Body Diagram: Ax & Ay Direction Matters?

[unknown_2]

hey, i just want a confirm if this is correct. imagine a built-in or a fixed bar in the side of a wall. when drawing a free body diagram for the point where the wall and the bar are fixed there should be forces in both x and y and a moment of force. if we label the x and y forces on the bar, does it matter on which direction we define it as?

ie

^  Ay                                                      
|                                                            
|                                                    
|                                                        
|----------->    Ax        


            OR


 | Ay
 |
 |
 |
\|/ <-----------  Ax

cuz, if you solve for Ax or Ay, even if it's -ve, it just means that positive motion is acting in the opposite direction...right?

any help would b appreciated.
cheers,

 

[Klockan3]

Physics is invariant under coordinate transforms, especially linear non accelerating coordinate transforms like this.

 

[astrokreng]

Hi there,

Thank you for sharing your question and diagram. You are correct, the direction of Ax and Ay do not matter when drawing a free body diagram. What is important is labeling the forces with the correct direction and sign, which you have shown in your diagrams. As you mentioned, a negative value for Ax or Ay simply indicates that the force is acting in the opposite direction, but it does not affect the overall analysis of the system.

In addition to the forces, it is also important to include the moment of force in the free body diagram, as you have mentioned. This is because the bar is fixed to the wall, so there will be a moment acting on the point where they are connected.

I hope this helps and clarifies your understanding of free body diagrams. Keep up the good work in your studies as a scientist!