Resultant force after adding a force to a couple moment?

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  • Thread starter nomisme
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  • #1
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I don't get it.
24mumo6.png


Imagine there is a stick leaning aganist a wall.
There is a moment couple somewhere on the stick.
The end of the stick hits the wall and the wall acts against it.

The sum of moment is 0 but since the moment couple forces cancel each other, the resultant force is the wall reaction force! which means the stick will move away from the wall!

But in reality i think the whole structure is stationary but not this!!!!!
 

Answers and Replies

  • #2
BvU
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Any difference with this picture ?
upload_2016-10-28_16-52-35.png
 
  • #3
A.T.
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the resultant force is the wall reaction force! which means the stick will move away from the wall!
Its center of mass will accelerate.

But in reality i think the whole structure is stationary
What makes you think this?
 
  • #4
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...the resultant force is the wall reaction force! which means the stick will move away from the wall!
If the stick moves away from the wall, the reaction force goes to zero. (At the point where the stick contacts the wall, the stick compresses the wall, and the wall compresses the end of the stick.)
 
  • #5
A.T.
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If the stick moves away from the wall, the reaction force goes to zero.
At some time point it will lose contact, but it stays in contact for a while and the contact force accelerates it.
 
  • #6
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…the moment couple forces cancel each other, the resultant force is the wall reaction force!
There is no net resultant linear force associated with couple itself. Linear forces cancel for a couple, so the applied load is a pure moment. The reaction force supplied by the wall creates a moment of force that is equal and opposite to the couple.
 
Last edited:
  • #7
A.T.
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There is no net resultant linear force.
Of course there is. It's equal to the contact force from the wall.

The reaction force supplied by the wall creates a moment of force that is equal and opposite to the couple.
There is no reason for these moments to be equal and opposite.
 
Last edited:

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