Demos: 2D-01 Hydraulic Press

Pascal’s Principle is demonstrated using a hydraulic floor jack set in a special frame to break a 2x4 board. In addition to Pascal’s Principle, the use of an arm extension demonstrates the lever principle.

Directions: Using the special handle, open the valve on the jack so that the piston can be lowered. Insert the 2x4 in the frame in such a way that the board will be crushed along its larger dimension. Close the valve and “pump” the jack in the usual manner. The board will be crushed with little effort on the part of the demonstrator.

The following data might be useful:

Pump piston diameter 0.5 in

Lift piston diameter 1.25 in

Leverage ratio of handle 16:1

The ratio of cross-sectional areas of the pistons is 6.25, which multiplied by the mechanical advantage of the handle, gives 16 x 6.25 = 100. This represents the mechanical advantage of the entire system. So if you exerted a force of, say, 10 lbs on the end of the handle, the output piston would exert a force of 1,000 lbs on the piece of wood.

Suggestions for Presentation: After presenting Pascal’s Principle in the form of the hydraulic lift, tell the students that you are going to crush the block of wood along its strongest direction with very little effort. After performing the demo, you might want to supply the pertinent data, namely the relative diameters of the two cylinders. These are printed on the jack. A little thought will show that the ratio of output and input forces isn’t large enough to crush the wood with such seemingly small effort. Then point out that the input force is greatly enhanced by the leverage gained using the long handle.

Applications: A variety of hydraulic jacks, chair lifts used in dentists’ offices, hydraulic-based lift mechanisms on machinery, aircraft, etc.

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