Every object on earth is either a solid, a liquid or a gas. How these objects behave (act) when pushed or pulled is called "dynamics".

The molecules (small particles) in a solid object stay in line so the object keeps its shape. If you try to push a square solid into a smaller round hole the solid will not change shapes. It might break, but it won't change shapes. And, no matter how hard you squeeze or stretch (pull) a solid, the molecules will not change position. (You cannot force the solid to become bigger or smaller.)

The molecules in a liquid, however, are different from a solid. If you pour a liquid from a square bowl (container) into a round bowl it will take on the shape of the round bowl. The liquid will gather together. It will not expand (become larger) to fit the container. If you squeeze or pull a liquid the molecules will not change position. (You cannot force the liquid to become bigger or smaller.)

Gases, like air, are different from both liquids and solids. Gases will change shape to fit a container. Gases will also expand (spread out) or contract (move close together) to fit the space available. The molecules in gases move (change position) when when pushed or pulled. Liquids and gases are fluids.

Dynamics will be studied in four areas: (1) dynamics of solids, (2) how liquids behave (hydrodynamics), (3) how air and other gases move (aerodynamics), (4) and how high speed gases change (gas dynamics). Each will be discussed in the next few pages.

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Last modified: Sat Jun 20 21:18:09 PDT 1998