Questions pertaining to Blender's internal physics or the Game Engine physics.
Blender has several internal physics systems. These physics systems allow you to simulate real-world interactions between various types of materials. Once you set up the scene, you can often "Bake" the simulation, which calculates the motion of the system and saves it for quicker playback.
The types of physics systems included in Blender are:
Soft Body – for any object that should be able to bend, twist, and stretch according to physical forces, such as a wind cone or hair. Tag: soft-body
Cloth – for any open object that should be able to bend, twist, and stretch according to physical forces, such as a flag or clothing. Tag: cloth-simulation
Fluid – to simulate interactions of fluids with the environment, including inflows (sources), outflows (sinks), and obstacles. Tag: fluid-simulation
Smoke – to simulate smoke, fire, or other similar volumetric entities. Tag: smoke-simulation
Rigid Body – to simulate objects that do not deform, but remain rigid on collisions. Tag: rigid-body-simulation.
Particles (includes hair simulation) – to generate large numbers of particles or objects, moving according to specified laws of physics. Tags: particleshair-particles
as well as Force Fields force-fields, which are used in conjunction with many of the simulators; dynamic paint dynamic-paint, which allows meshes to be used as "brushes" to paint or displace other meshes; and the Ocean modifier ocean-simulation, which simulates waves in an ocean.
Blender's Game Engine (BGE, game-engine) also has built in physics for Soft Body and Rigid Body dynamics. (see the wiki for more information on BGE physics systems)