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Help with free body diagram 
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#1
Feb313, 06:05 PM

P: 398

For the attached picture I need to draw a free body diagram for the structure supporting the pulley.
At the fixed end (left), there would be a vertical and horizontal reaction force as well as a moment. I am not sure what the forces and moments would be for the part connected to the pulley. What would it look like for this situation? 


#2
Feb313, 06:15 PM

P: 616

You're shown some of the forces. What others are missing?



#3
Feb313, 06:17 PM

P: 398

There should be a force where the pulley is attached, but I don't know what direction that should be in. EditI think there should be a reaction force where the pulley is connected in 'both' the x and y direction. 


#4
Feb313, 06:21 PM

P: 398

Help with free body diagram
There should also be a reaction moment where it's connected.



#5
Feb313, 07:06 PM

P: 616




#6
Feb313, 07:35 PM

P: 398




#7
Feb313, 08:06 PM

P: 616

Does the pulley exert any forces on the structure?
You've said the wall exerts a reaction force on the beam? What is it reacting to? 


#8
Feb313, 09:07 PM

P: 398

The wall holds the cantilever beam. It exerts a horizontal and vertical (maybe) force on the structure. It also exerts a moment because it's cantilevered.
The pulley is being held by the structure, so yes, it exerts a force which should be both in the horizontal and vertical direction. My question is if this is right and if there is a moment exerted as well. 


#9
Feb313, 09:30 PM

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There is no moment at the pulley, because the pulley bearings prevent this. But there is a vertical force and a horizontal force exerted by the pulley axis (spindle) on the structure.



#10
Feb313, 09:32 PM

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Are the bracket holding the pulley, and the pulley itself massive enough so the their masses have to be considered? 


#11
Feb313, 09:58 PM

P: 398

Thank you.
It seems Chestermiller and SammyS may have conflicting opinions on whether there should be a moment exerted where the pulley is attached. "Are the bracket holding the pulley, and the pulley itself massive enough so the their masses have to be considered?" I believe the structure is what's the pulley. I have as much info as you guys, so I'm not entirely sure. Typically for shear and moment diagram (which this is) problems, we ignore mass. This is what I assumed since they don't give you mass. I think I agree with Chestermiller that there isn't a moment exerted at where the pullley is. 


#12
Feb313, 10:00 PM

P: 398

Attached is what I think the free body diagram should look like.
Where the 4 arrows indicate the arbitrary reaction forces and the counter clock wise arrow represents the moment. 


#13
Feb313, 10:18 PM

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#14
Feb313, 10:31 PM

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#15
Feb313, 10:45 PM

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#16
Feb413, 05:12 AM

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When you talk about 'arbitrary' reaction forces and moment at the wall, I am not sure what you mean. You can arbitrarily choose their direction, I suppose, and their true directions will be determined when the equlibrium equations are applied. But their is no arbitation on their magnitudes (unknown until the equilibrium equations are applied), and no arbitration whatsoever in the magnitude and directions of the forces at the pulley end. 


#17
Feb413, 06:34 AM

P: 259

If the reactions are drawn in the wrong direction, then their value will come out negative. The magnitude should still be the same. And don't say that a beam exerts a moment because its cantilever, it exerts a moment because the fixed support prevents it from wanting to rotate. What if the beam was supported by a roller or pin? Neither one of those supports have a moment reaction



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