In: Physics
1. When determining the amount of work needed to pump something what would cause the final work to be negative?
2. What is the purpose behind integration in determining fluid force on vertical surfaces?
(1).
For a centrifugal pump or any pump its sole aim is to convert high pressure fluid at outlet of low pressure entering fluid. So from system we are getting some form of output that is pressure energy. For that to happen we need some energy input to the system and I.e. work input. So work is applied externally to the system to get higher pressure energy. Finally the work input is negative.
(2).
When a surface is submerged in a fluid, forces develop on the surface due to the fluid. The determination of these forces is important in the design of storage tanks, ships, dams, and other hydraulic structures.
When afluid that is standing still, the pressure p at depth h is
the fluid's weight-density w
times h: p = wh. If the fluid is pressing against a horizontal base
of a vat, then the total
force exerted by the fluid against the base is F = pressure * area
= whA.
If we would like to determine the force exerted by a fluid against
one side of a vertical
plate submerged in the fluid, then we would have to use the
variable-depth formula.
THE INTEGRAL FOR FLUID FORCE:
L (y) is the length of a horizontal strip from left to right at level y, and w is the weight density of the fluid.