What is the Objective of Propulsion?

The basic objective of propulsion is to move an animal or an object through a fluid (a liquid or a gas). The most common fluids utilized in propulsion are water and air. But many things remain fixed in space without any problems (rocks, trees, etc.), so why move? There are many reasons, but generally they can be categorized as follows:

We will discuss these three objectives in more detail in the following pages. At the end of this section we will introduce performance factors that must be considered to achieve these objectives.