Mass is a measure of inertia.

The question states $\dots$ four uncharged capacitor $\dots$

$\dots$ Is the vertical pressure force on the bottom of a liquid container equal the weight of the fluid above the surface area?

You have forgotten the effect of the walls of your container. Pressure at base of 3 different dam designs and Understanding Hydrostatic Pressure on a Microscopic Scale $\dots$

@Bucephalus The direction of a normal to an ideal corner is an interesting concept. With you two bits of rope, either side of the corner, you can always choose the normal to be one which bisects the angle.

@Bucephalus I have added a comment to your post to explain why the angles must be equal.

@Bucephalus I agree with you but that makes the answer to your question rather straight forward.

All corners are assumed to have no friction. This is quite an assumption!

@BaddDadd I entirely agree and so have corrected my answer.

Related Velocity of the points of a rigid body

Related -Clarifying the actual definition of elasticity. Is steel really more elastic than rubber?

@FlatterMann No, but the interference pattern intensity did not seem to change as I rotated the plane of polarisation. From the diffraction envelope I estimate the width of my slits to be approximately $50\,\mu\rm m$. Perhaps that is not narrow enough?