# Hydraulic Chairs

What mechanisms are used in raising or lowering chairs with hydraulic lifts?

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#### Solution Preview

Pascal's Principle.

If you have a container filled with liquid (which by nature is incompressible), and the container is fitted with a piston on top of which a block of steel rests, then the atmosphere, container, and the block of steel exert a pressure, pext, on the piston, and thus on the liquid. The pressure p at any point P in the liquid is given by

p = pext + pgh

where p is the density of the liquid, g is gravitational force, and h is the depth in the cylinder. Adding a second block of steel on top of the piston means that the pressure pext increases by the amount delta pext. Since the other quantities are unchanged, then the change in pressure at point P is the same as the change in pressure delta pext. Since this pressure change is independent of h, it must hold for all points in the liquid, as Pascal's principle states.

The Hydraulic Lever

This operates ...

#### Solution Summary

This solution identifies Pascal's principle for pressure, how hydraulic lifts work and how the office chair works using pneumatic lifting (or gas pressure). The attachment provides diagrams and formulas to help understand the concepts. 650 words.