What is Pascal's Principle? Video

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  • 0:02 Pascal's Principle
  • 1:00 How Pascal's Principle Works
  • 2:49 Examples
  • 4:49 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Feeling pressured to learn about Pascal's principle? Then you came to the right place. Pascal's principle states that a change in pressure at any point in an enclosed fluid is transmitted equally throughout that fluid. See examples and learn more.

Pascal's Principle

If there's one thing I hate, it's car trouble. Fortunately, I have a friend who's an auto mechanic. If my car is not running right, I take it over to his shop where he has all the equipment needed to get my car back on the road. At his shop, he is able to give my car a thorough look over by lifting it up using a large jack. Jacks, like the ones used by car mechanics, work because of hydraulics, which are simply fluids under pressure.

We understand how hydraulics work thanks to Pascal's principle, which states that a change in pressure at any point in an enclosed fluid will be transmitted undiminished to all parts of that fluid. In this lesson, we will learn more about hydraulics and other applications of Pascal's principle to see how the principle is employed to make jobs easier.

How Pascal's Principle Works

One of the easiest ways to learn about Pascal's principle is by using a U-shaped tube filled with water. If we plug both ends with freely moving pistons, we create a closed system. If we push down on the left piston, we will see the piston on the right moves up (please see the video at 01:19). This movement happens because the force we applied at the first piston was transmitted to the second piston using the incompressible water.

Knowing this, what do you think would happen if we made the tube on the right wider and increased the area of the piston? Well, in this case, the force you apply to the smaller piston will make the wider piston rise slowly but with a lot more force. In fact, this is how hydraulics work. Because the fluid cannot be compressed, the pressure remains constant throughout it. Pressure is the force exerted over a given area. So, if you press down with a small force on a piston with a small area, there must be a large force acting on the larger area piston to keep the pressure the same.

In our experiment, we used water, but we know from Pascal's principle that any enclosed fluid will work. A fluid is defined as any substance that flows and that takes the shape of its container. Therefore, both liquids and gases are fluids. Knowing this, we see that Pascal's principle can be demonstrated using an air-filled balloon. When you squeeze a balloon, you exert pressure on the closed system. That pressure is transmitted equally throughout the air, causing the flexible walls of the balloon to bulge out in all possible directions.

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