## Introduction

You have successfully finished your first lab! In order to continue, we must start to define some terms and definitions. In other words, we need to start talking the language of "Pneumatics".

## Terms and Definitions

### Pressure

The first term and one of the most important terms that we need to cover is "Pressure". Pressure is the intensity of force. It is created when a force from one object acts over an area of another object. Look at the following picture.

Parker Hannifin Corp. (1980). Industrial Pneumatic Technology Bulletin 0275-B1. Parker Hannifin Corp.

For example, the weight of the box creates a total force of 100 lbs on the surface on which it is resting. However, the force is actually distributed evenly over the entire area of 100 square inches. (Count the small squares if you don't believe me.) This means that a percentage of the total force (100 lbs) acts on each square inch of the surface. In this case, it would be 1 lb for each square inch. This creates a unit of pressure called "psi". In this case, it would be 1 psi (1 lb per square inch).

In other words, pressure is determined by the force and the area.

Some Algebra:

The following shows the mathematical formulas for finding pressure.

Mathematical Expression for Pressure

- - - - - - - P - pressure, F - force, A - surface area

P = (F / A) < or > P = F : A

- - - - - - - Most common units are:
              - English: pounds/inches2 (psi)
              - SI: Newtons/meter2 (pascal - Pa)

This algebraic mathematical equation makes it possible to design systems. (Yes, you will be doing some algebra. Don't stress). When you know 2 of the variables, you can figure out the 3rd. We will practice this in the quiz that follows.

Pascal's Law

One more principal we need to talk about is Pascal's Law. In the example above, we were talking about mechanical distribution of force. 100 lbs spread out over an area of 100 square inches will give us 1 psi. Gas also produces pressure. This is called fluid pressure, and in the case of pneumatics, that would be air pressure. A simple way to create air pressure is to place a weight on top of a container of air. See the following picture.

Parker Hannifin Corp. (1980). Industrial Pneumatic Technology Bulletin 0275-B1. Parker Hannifin Corp.

As you can see, a certain weight is placed on top of a container full of air. Assuming that the container and the weight are sealed, the weight then reduces the volume and creates pressure to support the weight. The amount of air pressure in the container is calculated using the formula: Pressure = (Force/Area). Which, in this case, is 100 lbs divided by 100 square inches, which means the container has 1 psi. A Frenchman named Luis Pascal stated, a long time ago, that the air pressure will be the same at every point in the container. This concept, along with the mathematical formula above, has an application with pneumatic cylinders and compressors. We will learn more about this as we progress.

Cool side note: Do you realize that you walk around every day with about 14.7 psi pressing against you? 14.7 psi is the actual pressure that is created by the weight of the atmosphere. This pressure changes depending on where you live: sea level = higher pressure; Mt. Everest = lower pressure.

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