Movement of each of the components of the Boulton & Watt Steam Engine (1784) can be described by a set of equations of kinematics and kinetics.
In thephysical science of dynamics,rigid-body dynamics studies the movement ofsystems of interconnectedbodies under the action of externalforces. The assumption that the bodies arerigid (i.e. they do notdeform under the action of applied forces) simplifies analysis, by reducing the parameters that describe the configuration of the system to the translation and rotation ofreference frames attached to each body.[5][6] This excludes bodies that displayfluid, highlyelastic, andplastic behavior.
The dynamics of a rigid body system is described by the laws ofkinematics and by the application of Newton's second law (kinetics) or their derivative form,Lagrangian mechanics. The solution of these equations of motion provides a description of the position, the motion and the acceleration of the individual components of the system, and overall the system itself, as afunction of time. The formulation and solution of rigid body dynamics is an important tool in the computer simulation ofmechanical systems.
Computer generated animation of fluid in a tube flowing past a cylinder, showing theshedding of a series ofvortices in the flow behind it, called avon Kármán vortex street. Thestreamlines show the direction of the fluid flow, and the color gradient shows the pressure at each point, from blue to green, yellow, and red indicating increasing pressure
Fluid dynamics offers a systematic structure—which underlies thesepractical disciplines—that embraces empirical and semi-empirical laws derived fromflow measurement and used to solve practical problems. The solution to a fluid dynamics problem typically involves the calculation of various properties of the fluid, such asflow velocity,pressure,density, andtemperature, as functions of space and time.
Before the twentieth century, "hydrodynamics" was synonymous with fluid dynamics. This is still reflected in names of some fluid dynamics topics, likemagnetohydrodynamics andhydrodynamic stability, both of which can also be applied to gases.[7]
