Citation

Evans FG. Proc. Am. Assoc. Automot. Med. Annu. Conf. 1961; 5: 144-157.

Copyright

(Copyright © 1961, Association for the Advancement of Automotive Medicine)

DOI

unavailable

PMID

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Abstract

An understanding of the mechanics of bone fracture involves some knowledge of certain basic principles of mechanics or the effect of forces upon the form or motion of bodies. A force is anything tending to change the state of a body with respect to its motion or the relative position of the molecules composing it or, more simply defined, a push or pull. There are three kinds of primary forces: (1) tensile or pulling apart forces, (2) compressive or pushing together forces, and (3) shearing or forces which make one part of a body slide on an immediately adjacent part, i.e., the action of scissors in cutting.

The rate at which a force is applied to a body, i.e., slowly (statically) or suddenly (dynamically), is important because a body can support a greater load or force without breaking if it is slowly rather than suddenly applied. The duration of the load and whether it is applied steadily, intermittently or repetitively also influence the behavior of a body. When a force is suddenly applied, as by a blow or impact, the energy involved must be considered because the ability of a body to absorb or store energy is an important factor in determining whether or not failure (fracture) occurs. From the viewpoint of mechanics, it is more correct to speak of the energy of a blow than the force of a blow. Force and energy are two different phenomena and can not be compared directly with one another. Force is measured in units of pounds or kilograms while energy is measured in terms of inch pounds/cubic inch or kilogram centimeters/cubic centimeter.