Atwood number, abbreviated as A, a dimensionless number, describes density difference between two adjacent fluids with a common interface. Atwood number is an important parameter in the study of Rayleigh–Taylor instability and Richtmyer–Meshkov instability. In Rayleigh–Taylor instability, the penetration distance of heavy fluid bubbles into the light fluid is a function of acceleration time scale.
Atwood Number Calculator
ATwood number formula