How is the slope of the shear force equal to the negative of the load?

[Svelte1]

Homework Statement

dV/dx=-W

Relevant Equations

dV/dx=-W

At any point between A and C the point load is negative (downwards), in the shear force diagram: positive is upwards, so this slope is negative. The equation says the slope should be positive. Is this something to do with shear force sign convention?

 

[erobz]

Personally, I don't think I've ever understood the shear convention myself. I thought it acts to oppose the external forces on the beam so that the beam remains static, but I'm not sure now. I look forward to hearing other's thoughts on the matter.

 

[haruspex]

At https://wp.optics.arizona.edu/optomech/wp-content/uploads/sites/53/2016/10/OPTI_222_W8.pdf, they seem to take q as a magnitude, and the equation dV/dx=-q is assuming it represents a load. Hence, effectively, the load convention is positive down.

 

[erobz]

So based on the convention given in the paper that @haruspex shared, the shear being positive from $\rm{A}$ until around $x_1 = 5.7 \rm{m}$ where $V=0$ means the beam is deflecting like:

and after $x_1$ the beam in deforming like the mirror image of that:

 

[Svelte1]

Ok, thanks guys. Assuming it's a load makes sens I suppose. Also I have a lot of questions around this level in the coming weeks, is this the correct forum for that? Thanks.

 

[haruspex]

is this the correct forum for that? Thanks.

Should be fine, but there is also
https://www.physicsforums.com/forums/engineering-and-comp-sci-homework-help/