Terminal Fall Velocity

The terminal fall velocity is describes the maximum velocity a particle can achieve when falling through an atmosphere.in effect since aerodynamic drag increases with velocity, a point will arise during the fall of an object where its increase in velocity due to the gravitational force will be balanced by the force of aerodynamics drag that slows its descent. At this point the particle can fall no faster and so is said to have reached its terminal velocity.

Terminal velocity = C_d `sqrt` dg`rho`/`beta`
 Where :

• c_d is the aerodynamic drag coefficient (which is 1.054 for volcanic ash)
• D is the particle diameter
• G is the acceleration due to gravity
• `Rho` is the particle density
• `Beta` is the atmospheric density