fluid head pressure calculation

[Gary Thornton]

Could someone tell me how to calculate the head pressure exerted at a
particular height in a cylinder if the top of the cylinder is covered
by a floating top given fluid density, cylinder diameter, and wieght
of top ?

[RichardSchwartz]

If the top is truly floating in the fluid, and is supported by it, there
will be a small gap of fluid between the top and the walls of the
cylinder. THE TOP HAS NOTHING TO DO WITH THE PRESSURE! The pressure at
any depth below the surface of the fluid is the depth times the density
of the fluid.

However, if the top makes a tight seal with the walls of the cylinder, it
is a different story. Now the top is sitting on an incompressible fluid,
rather than floating in it. Assuming there is zero friction with the
cylinder walls (an assumption all physics students like to make), and a
scantily clad California beach girl is not sitting on the top, then the
pressure in the fluid is the weight of the top divided by the area of the
top, PLUS the density of the fluid divided by the depth of the fluid.