We believe the earliest flights began with the dinosaurs. Giant flying reptiles larger than the largest birds seen today terrorized the skies some 100 million years ago. Actual glider models have been produced by paleontologists based on fossil records of the creatures. But we can only guess how far and how high they flew.

Most paleontologists do agree that these flying dinosaurs are closely related to the birds. Some scientists also argue that the bird is the closest living relative of the dinosaur. Other flying creatures, including insects and mammals such as bats, were said to have evolved in different ways.

An American Golden Eagle in flight

The flights of birds, dinosaurs, and aircraft are explained by basic principles of physics, which will be discussed in greater detail in a few chapters. For now, but I’ll give you a foundation to help build your knowledge. Some of you may still be under the mistaken notion that “there is no there there” in the air (greatest apologies to Gertrude Stein for messing up her famous line). Yet air is not empty; it is full of trillions of nitrogen, oxygen, and carbon dioxide molecules as well as other microscopic particles.

Air is very similar to the liquid of the oceans. The only real difference is the obvious one: the air in our atmosphere is composed mainly of gas, and the ocean is composed mainly of liquid. How do fish move about in the ocean? They move fins, tentacles, and other surface areas through the mass of liquid. Liquid and air are both fluids. The water is more dense than the atmosphere, but they share similar characteristics.

You also need to know that as a fluid increases its velocity, its resulting pressure decreases. This describes Bernoulli’s Principle, which explains much of the lift of an airfoil. Also, for every action, there is an equal and opposite reaction. That statement describes Newton’s Third Law of Motion. These two physical constants allow us to understand how flight in the fluid atmosphere is possible. The fluid wind passes over the top of a bird’s wing faster than it passes across the bottom of the wing. The difference in velocity results in a difference of pressure, which causes a lifting effect on the wing. When birds flap their wings, they create an equal and opposite reaction against their bodies, which propels them through the atmosphere.

How birds manipulated these properties of the air was unknown for quite some time. Many felt it was the construction of the feather, which is remarkably light in proportion to its strength. The famous Greek legend of Daedalus and Icarus describes how the father and son, who were imprisoned on the island of Crete, made wings of wax and feathers to escape. They were speedily flying from the island when the over-exuberant son, Icarus, flew too close to the sun. The wax melted, and he plummeted to the sea and his death. In like manner, many throughout history have attempted to attach feathers to their arms and fly—some with deadly consequences—from cliffs, buildings, and mountains.

But important inventors and scientists gradually unlocked the secrets of the birds. Even if we never fly exactly as birds do, we can learn to build machines to carry us in flight. Machines are at the heart of this lecture’s discoveries.