For small meteoric bodies, terminating high in the atmosphere (i.e.
under free molecular conditions) it was possible to neglect the effect of thermal motions of air particles. As regards fireballs, bodies with masses in excess of about 0.1 kg, penetrating deep into the atnosphere, the ambient atmosphere has the properties of a continuous medium. Under these conditions, the thermal motions of atmospheric particles behind ťhe shock wave become
the decisive factor for momentum and energy transfer to the meteoroid. F'or fireballs these thermal motions practically replace the effect of direct impacts of particles of hie undisturbed atmosphere, considered earlier under free molecular conditions. The form of the equations, describing the motion and ablation of a large body (fireball) will remain the same as for small bodies, but the coefficients occurring in the equations will have a different
physical meaning.