PASCAL’S PRINCIPLE Chapter 8

Lets Review… What is pressure? What is the equation for pressure? What causes fluid pressure? When you catch a deep-sea fish, why does its eyes pop-out? Why do your ears pop on an airplane or up in the mountains?

Pascal’s Principle When force is applied to a confined liquid, the change in pressure is transmitted equally to all parts of the fluid. Draw a mental picture of a bottle of water with arrows to illustrate the regular exerted pressure. Then draw a water bottle that you squeeze. What happens to the pressure? What happens if you open the top? How does Pascal’s Principle explain what happens if you squeeze a water bottle?

A force applied to one section of an enclosed liquid at rest will be transferred to the entire liquid with the same amount of force.

Pascal’s Principle & Hydraulic Lifts A force F 1 is applied to a hydraulic press. This increases the pressure throughout the oil, lifting the car--Pascal’s principle. This would not work with air, since air is compressible. The pressure is the same throughout the oil (since the effect of depth is negligible), so P = F 1 /A 1 = F 2 /A 2  F 2 = (A 2 / A 1 ) F 1 Since A 2 > A 1 the applied force is magnified by the ratio of the areas. A force F 1 is applied to a hydraulic press. This increases the pressure throughout the oil, lifting the car--Pascal’s principle. This would not work with air, since air is compressible. The pressure is the same throughout the oil (since the effect of depth is negligible), so P = F 1 /A 1 = F 2 /A 2  F 2 = (A 2 / A 1 ) F 1 Since A 2 > A 1 the applied force is magnified by the ratio of the areas.

Hydraulic Systems A force applied to one piston increases the fluid pressure throughout the fluid. If the second piston has a larger surface area, the force is multiplied! Pressure = Force/Area Force/Area = Pressure = Larger Force/Larger Area