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Fig. 1. A portion of a sperm flagellum that is propagating a bending wave, shown at
two points in time in A and B. If the bending wave is moving from left to
right, a short segment (dark bar) will be moving up in A and down in B,
changing its tilt as the velocity changes. The velocity, V, of any
segment can be resolved into a longitudinal component, VL,
and a normal component, VN. Resistive force theory states
that the force components pushing on the fluid will then be
FL=CLVL and
FN=CNVN, where
CL and CN are resistance constants. If
CN>CL, the total force
F=FN+FL will always have a
component pushing on the fluid in the direction of wave propagation, and this
will provide a thrust in the opposite direction, propelling the spermatozoon
to the left.
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