The science of biomechanics applies mechanical principles to the study of organisms. Biomechanics uses mathematical models and computer simulations to study living organisms, in addition to direct biological measurements.

Biomechanics helps us understand limitations on the size of organisms, problems with scaling, energy efficiency, the advantages of internal versus external skeletons, and other concepts. Biomechanics can even help biologists understand animal behavior, such as how a whale can remain submerged for extended periods of time.

For example, the largest single-celled organisms are protists about the size of the period at the end of this sentence. There are larger cells that are part of multicellular organisms, but no single-celled organisms. So why are there no large, single-celled animals? The primary restriction is surface-to-volume ratio. A cubical cell 100 μm on a side has a volume and mass 1,000 times as great as the volume and mass of a cell 10 μm on...