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Particle velocity (denoted v or SVL) is the velocity of a particle (real or imagined) in a medium as it transmits a wave. The SI unit of particle velocity is the metre per second (m/s). In many cases this is a longitudinal wave of pressure as with sound , but it can also be a transverse wave as with the vibration of a taut string.
Quantity (common name/s) (Common) symbol/s Defining equation SI units Dimension Number of atoms N = Number of atoms remaining at time t. N 0 = Initial number of atoms at time t = 0
One particle: N particles: One dimension ^ = ^ + = + ^ = = ^ + (,,) = = + (,,) where the position of particle n is x n. = + = = +. (,) = /.There is a further restriction — the solution must not grow at infinity, so that it has either a finite L 2-norm (if it is a bound state) or a slowly diverging norm (if it is part of a continuum): [1] ‖ ‖ = | |.
The equation predicts that for short range interactions, the equilibrium velocity distribution will follow a Maxwell–Boltzmann distribution. To the right is a molecular dynamics (MD) simulation in which 900 hard sphere particles are constrained to move in a rectangle.
Consider a free particle of mass with equation of motion described by = + (), where = / is the particle velocity, is the particle mobility, and () = is a rapidly fluctuating force whose time-average vanishes over a characteristic timescale of particle collisions, i.e. () ¯ =.
Alternatively the final velocity of a particle, v 2 (v A2 or v B2) is expressed by: = (+) Where: e is the coefficient of restitution. v CoM is the velocity of the center of mass of the system of two particles: = + +
Equation [3] involves the average velocity v + v 0 / 2 . Intuitively, the velocity increases linearly, so the average velocity multiplied by time is the distance traveled while increasing the velocity from v 0 to v, as can be illustrated graphically by plotting velocity against time as a straight line graph. Algebraically, it follows ...
Letting = =, the mass of the particle, the integrated Boltzmann equation becomes the conservation of mass equation: [8]: 12, 168 + =, where = is the mass density, and = is the average fluid velocity.