4.1
Introduction to Fluid Mechanics

In 1903, at Kitty Hawk, North Carolina, Orville and Wilbur Wright flew their homemade airplane for 59 seconds, travelling in the air a distance of 260 meters. Their aircraft is generally recognized as the first heavier-than-air, powered vehicle, meaning that anything that flew before then was either a glider, a balloon, a blimp, or a bird.[1]

Although rocket technology is a whole different field, it’s nonetheless interesting to note that it was only 66 years later – less than a human lifetime – that the first human beings walked on the surface of the moon. Somebody could have witnessed, as a child, the first airplane to ever take to the sky, and then grown up and gotten on a commercial airliner to Florida to watch Neil Armstrong and Buzz Aldrin take off in a Saturn V rocket.

Through most of the chapters so far, we’ve been talking about the physics of solid objects that can’t be bent or squished. Of the three most common phases of matter – solids, liquids, and gases – the physics of solids have historically been the big stars of the physics world, and there’s a simple reason for this: liquids and gases are hard to get a handle on, because they always change their own shapes to fit whatever container they’re in. Worse yet, gases will actually expand or contract to fill up the space around them. And until more sophisticated devices were developed, it was always a bit trickier to measure something like the speed of water in a tube than it was to time a falling rock, for example.

Nevertheless, thanks to persistence and ingenuity, physicists eventually figured out how non-solid stuff works, allowing us to build airplanes, design hydraulic systems, and solve medical problems involving the heart and blood flow.

Although the word ‘fluid’ commonly means a liquid, physicists use it to refer to anything that isn’t solid – i.e. liquids and gases. In this chapter, we’ll go through just a few of the basic properties of fluids and then jump into a discussion of airplane flight.

It all started, of course, back in Ancient Greece…

1. Other possibilities include a bee, a bat, and a pterodactyl.
4.1 Introduction to Fluid Mechanics   (from Chapter 4: Fluid Mechanics)