Internal Shear Stress Question

AI Thread Summary
The discussion centers on a common figure in statics textbooks that illustrates the application of delta V to shear forces and moments. The original poster questions how adding delta V to the shear force on the right side maintains equilibrium, as it seems to create a net downward force. After contemplating the issue, they realize that delta V may actually be negative, which clarifies their confusion. This insight leads to a better understanding of the equilibrium conditions presented in the figure. The conversation highlights the importance of correctly interpreting the signs of forces in statics problems.
rat4x4
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Something has been bugging me for a long time, since I took my first statics class a few years ago. I have a problem with a common figure found in many statics books. I have attached the figure to my post.

My question deals with the delta V added to the shear force on the right side of the figure. According to the textbooks, both the shear force and moment acting on the right-hand face must be increased by a small, finite amount in order to keep the segment in equilibrium. But wouldn't this take the segment out of equilibrium? I mean, you have the resultant loading acting downwards, and then you have a shear force on the right-hand face acting downwards which itself is greater than the shear force on the left hand side. Summing the forces in the y direction, wouldn't there be a net force downwards?

What am I missing here? Why does this not make sense to me and why is this figure so common in statics books?
 

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OK, I believe that I have figured it out. Perhaps the delta V is negative and I have always taken it to be a positive quantity.
 
Wow, what a stupid question. Sorry guys.
 

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