# Cauchy number

From AMS Glossary

## Cauchy number

(Also Hooke number.) In fluid mechanics, a dimensionless group that arises in the study of compressible flow.

The square of the Mach number, its physical interpretation is the ratio of inertia force (ρ

*U*^{2}) to compressibility force (1/κ), where ρ is density,*U*is a characteristic speed, and κ is compressibility.