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Pascal’s Principle and Hydraulic Car Lifts

Pascal's Principle – Pressure applied to a completely enclosed fluid is transmitted undiminished to all parts of the fluid and the enclosing walls.

(F2/A2) = (F1/A1)

Two cylinders joined have the same pressure.  The one with the larger surface area exerts more force.


The figure displays two joined cylindrical chambers. They both have different diameters and including the connecting tube, are filled with liquid. Since the second piston is larger, it produces a larger force than the force applied to the smaller piston:

F2 = F1(A2/A1)


The hydraulic car lift relates to Pascal's Principle. It’s used in garages to lift a car off the ground for repairs. A small force by a small-area piston can be converted to a large force at a large area piston. It works relatively close to a lever, where a small force passes through a great distance to transport a heavy object a short distance. The work is the same when lifting the heavy object or when applying a small force. In the case of a lever a bar and a fulcrum convert the work, in the hydraulic lift the fluid performs the work.


A hydraulic car lift has a pump piston with radius r1 = 0.0120 m. The resultant

piston has a radius of r2 = 0.150 m. The total weight of the car and plunger is F2 = 2500 m. If

the bottom ends of the piston and plunger are at the same height, what input force is

required to stabilize the car and output plunger?

Answer: We need to use the area for circular objects, A=3.14r2 for both the piston and

plunger. Apply Pascal's Principle:

F1= F2(A1/A2) = F2(3.14r2/3.14r2) = (20 500N)[(0.01202)/(0.1502)] = 131 N

review Pascal's Principle

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Ajit Srinivas

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