Week 24 - Hydraulic Systems and the Development of Mechanical Devices

Lesson 10

Read pages 293 - 302

Lesson 10:

We live inside a pressurized system - the atmosphere, and within us we have another pressurized system - our circulatory system. Our daily lives bring us into contact with many forms of pressurized devices. Whether its a bottle of pop, scuba tanks for breathing under water or a giant earth moving machine, pressurized systems make our lives easier and more entertaining. Now let's find out the scientific principles behind pressure.

Did You Know? Scuba divers must know and understand all about pressure. As they go deep underwater, the pressure of the water above them changes how their bodies react to the air they are breathing from their tank. This is one situation where what you don't know can kill you. But understanding the scientific principles about pressure allows divers to safely explore the underwater environment.

Calculating Pressure

Pressure (P) can be defined as the amount of force (F) applied over a known area (A), generally in square metres.

Pressure is measured in newtons per square metre . This unit is called a pascal (Pa) .

However, this is a very small unit of pressure, so generally we use kilopascals ( thousands of pascals)

Exercise 4.1: Pressure


Fooling Around With Pressurized Systems

If you get a chance to talk to a scientist she'll probably tell you that what she does for a job is fun. Pascal had fun playing with numbers. Pascal was a scientist who is known not only for his work on pressure but also in mathematics and theology. Through his experimentation and research he developed what is know today as Pascal's Law of pressure.

Pascal's law states that when pressure is applied to a liquid in an enclosed container the pressure (force) is transmitted equally and undiminished throughout the liquid in all directions.

For example, examine the hydraulic jack below. The pressure is equal throughout the jack. And because of this fact, some amazing things happen. Look at the diagram below. Do you see anything unusual?

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