Figure 2.
Hydrodynamic forces acting on the body model. Two snapshots at different time instants are shown with a lateral offset for clarity. The main body experiences resistive drag force fo. The tail receives reactive hydrodynamic forces, f1 and f2, owing to the mass of fluid pushed in the lateral direction of the oscillating body. In steady swimming, the average reactive forces in the x-direction (thrust) balance the resistive drag. Reactive forces in the y-direction would balance the lateral resistive drag on the main body (not shown) if it were not constrained to only move in the x-direction. (Online version in colour.)