# scallop theorem

## EnglishEdit

### EtymologyEdit

From an explanation of a principle of fluid dynamics given by E. M. Purcell

### NounEdit

**scallop theorem** (*plural* **scallop theorems**)

- (fluid dynamics) A theorem which states that to achieve propulsion at low Reynolds number in simple (i.e. Newtonian) fluids, a swimmer must deform in a way that is not invariant under time-reversal.