Biomechanics borrows and extends engineering techniques to study the mechanical properties of
organisms and their environments. Like physicists and engineers, biomechanics researchers tend to
specialize on either fluids or solids (but some do both). For solid materials, the stress–strain
curve reveals such useful information as various moduli, ultimate strength, extensibility, and work
of fracture. Few biological materials are linearly elastic so modified elastic moduli are defined.
Although biological materials tend to be less stiff than engineered materials, biomaterials tend to
be tougher due to their anisotropy and high extensibility. Biological beams are usually hollow
cylinders; particularly in plants, beams and columns tend to have high twist-to-bend ratios. Air and
water are the dominant biological fluids. Fluids generate both viscous and pressure drag (normalized
as drag coefficients) and the Reynolds number (Re) gives their relative importance. The no-slip
conditions l…