Unable to understand how these two forces are equal

In summary, the conversation discusses the concept of N1=f and N2=W being proven through balancing vertical and horizontal forces on an object in static equilibrium. The location of these forces is important for the moment they induce, but when analyzing translational equilibrium, they can be relocated to the center of mass of the object without affecting the equilibrium conditions. The links provided further explain this concept.
  • #1
tbn032
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In the solution given in the above image, I am unable to understand and prove why N1=f and N2=W. I have tried balancing the torque on different point but still unable to prove. Explain how N1=f and N2=W can be proved.
The justification for N1=f and N2=W which I have so far read is that it is just balancing the vertical force with vertical force and the horizontal force with horizontal force which are being applied on the object since the object is at equilibrium. My confusion with that is that the vertical and horizontal forces are being applied at different position of the object, how can they be directly compared so that the ladder is in equilibrium.
 
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  • #2
The object is solid and strong enough to transfer these forces from one end to the other.
The object is in static equilibrium; therefore, all the forces and moments created by them must be cancelling each other.
All the reactive forces and moments counteract the force of the weight and any moment that it induces.

Without those being present, the weight force will acelerate the object downwards, without inducing any rotation.
Imagining that it could be possible, without the weight force, those reactive forces will move and rotate the object in diferent directions.
 
  • #3
Lnewqban said:
The object is solid and strong enough to transfer these forces from one end to the other.
The object is in static equilibrium; therefore, all the forces and moments created by them must be cancelling each other.
All the reactive forces and moments counteract the force of the weight and any moment that it induces.
Since the object is at equilibrium, I understand that the vector sum N1+N2+W+f=0 and the vector sum of torque generated by these forces =0.but I do not understand how can the vertical forces be compared directly with vertical forces and horizontal force directly compared with horizontal force resulting in N1=f and N2=W even after they are being applied at different position.
 
  • #4
Since the balance of moments is not confusing to you, just relocate all those forces to the center of mass of the object.
The actual location of each of those forces is only important for the moment it induces.
 
  • #5
Lnewqban said:
jus relocate all those forces to the center of mass of the object.
Is relocation of forces which being applied at different position of the object to the center of mass of thr object which is at equilibrium allowed?if it is allowed, can you explain the concept behind it.
 
  • #6
tbn032 said:
Is relocation of forces which being applied at different position of the object to the center of mass of thr object which is at equilibrium allowed?if it is allowed, can you explain the concept behind it.
Yes, you may do that when you are analyzing translational equilibrium only.
For this first equilibrium condition for the static equilibrium (no translational acceleration) of a rigid body, the distances of the external forces to the center of mass are irrelevant.

Please, see:
https://courses.lumenlearning.com/s...apter/12-1-conditions-for-static-equilibrium/

https://courses.lumenlearning.com/suny-osuniversityphysics/chapter/9-6-center-of-mass/
 
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FAQ: Unable to understand how these two forces are equal

What are the two forces that are being referred to?

The two forces that are being referred to are the forces of gravity and the normal force.

How are these two forces equal?

These two forces are equal because they are acting in opposite directions with the same magnitude. The normal force is equal to the force of gravity acting on an object, but in the opposite direction.

Why is it important to understand how these two forces are equal?

Understanding how these two forces are equal is important in understanding the equilibrium of an object. When these forces are equal, the object is at rest or moving at a constant velocity.

Can these two forces ever be unequal?

Yes, these two forces can be unequal in certain situations. For example, if an object is accelerating, the normal force may be greater than the force of gravity, or vice versa.

How can I visualize the equality of these two forces?

You can visualize the equality of these two forces by picturing a scale. The normal force and the force of gravity are like two weights on opposite sides of the scale, balancing each other out.

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