1. The branch of mechanics that is concerned with the effects of forces on the motion of a body or system of bodies; especially, of forces that do not originate within the system itself.
2. The forces which tend to produce activity and change in any situation or sphere of existence.
3. In music, the different levels of loudness and softness in a piece of music or the variation in the intensity or volume of musical sound, and the way in which a performer reproduces them during a performance.

The application of computer technology to make quantitative analyses and predictions concerning the behavior of fluids: The computational fluid dynamics predicts the behavior of fluids in motion and of the effects of movements around objects by using numerical methods.

The scientific study of fluids in motion; such as, gases and liquids.

1. In mechanics, a body which does not change its shape or size regardless of the force applied to it; that is, the relative position of its component particles is absolutely fixed in positon relative to each other.
2. An actual body whose behavior approaches that of an ideal rigid body; such as, a steel beam.
3. An idealized extended solid whose size and shape are definitely fixed and remain unaltered when forces are applied.

The rigid body assumption is a mathematical convenience that is useful and gives correct results for many important phenomena.