Early humans had to endure whatever nature provided. Only within the last few thousand years have agriculture and technology provided some level of control over the environment. And it has been a mere couple of centuries since machines, and later electronics, began to do much of our work and provide us with “creature comforts.”

It’s no coincidence that machines began to appear about a century after Galileo, Newton, and others ignited what we now call the scientific revolution. The machines and other devices we take for granted today are direct consequences of scientific knowledge and the scientific method.

Parts I and II have established Newton’s theory of motion, the foundation of modern science. Most of the applications will be developed in other science and engineering courses, but we’re now in a good position to examine a few of the more practical aspects of Newtonian mechanics.

Our goal for Part III is to apply our newfound theory to three important topics:

• Rotation. Rotation is a very important form of motion, but to understand rotational motion we’ll need to introduce a new model—the rigid-body model. We’ll then be able to study rolling wheels and spinning space stations. Rotation will also lead to the law of conservation of angular momentum.

• Gravity. By adding one more law, Newton’s law of gravity, we’ll be able to understand much about the physics of the space station, communication satellites, the solar system, and interplanetary travel.

• Fluids. Liquids and gases flow. Surprisingly, it takes no new physics to understand the basic mechanical properties of fluids. By applying our understanding of force, we’ll be able to understand what pressure is, how a steel ship can float, and how fluids flow through pipes.

Newton’s laws of motion and the conservation laws, especially conservation of energy, will be the tools that allow us to analyze and understand a variety of interesting and practical applications.