Introduction
The movement of particles may be controlled in a multitude of ways. Here we will discuss only the particle physics in the narrower sense, i.e. the settings in the Physics panel.
Additional ways of moving particles are:
By soft body animation (only for Hair particle systems).
By force fields and along curves.
By lattices.
Common Physics Settings
Size
Sets the size of the particles.
Random Size
Give the particles a random size variation.
Mass
Specify the mass of the particles.
Multiply Mass with Particle Size
Causes larger particles to have larger masses.
No Physics
The particles will be given no motion, which makes them belong to no physics system. At first a physics type that makes the particles to be static could seem a bit strange, but it can be very useful at times. None physics make the particles stick to their emitter their whole life time. The initial velocities here are for example used to give a velocity to particles that are affected by a harmonic effector with this physics type when the effect of the effector ends.
Moreover, it can be very convenient to have particles at disposal (whose both Unborn and Died are visible on render) to groom vegetation and/or ecosystems using Object or Group types of visualization.