It must be evident, however, that this case has nothing in common with either the ordinary 'static' tests of structural materials in testing-machines, or with impact tests."[13] [Footnote 13: Johnson, J.B.: The materials of construction, pp.
81-82.] (3) ~Impact, shock,~ or ~blow.~[14] There are various common uses of wood where the material is subjected to sudden shocks and jars or impact.

Such is the action on the felloes and spokes of a wagon wheel passing over a rough road; on a hammer handle when a blow is struck; on a maul when it strikes a wedge.
[Footnote 14: See Tiemann, Harry D.: The theory of impact and its application to testing materials.Jour.Franklin Inst., Oct., Nov., 1909, pp.

235-259, 336-364.] Resistance to impact is resistance to energy which is measured by the product of the force into the space through which it moves, or by the product of one-half the moving mass which causes the shock into the square of its velocity.

The work done upon the piece at the instant the velocity is entirely removed from the striking body is equal to the total energy of that body.

It is impossible, however, to get all of the energy of the striking body stored in the specimen, though the greater the mass and the shorter the space through which it moves, or, in other words, the greater the proportion of weight and the smaller the proportion of velocity making up the energy of the striking body, the more energy the specimen will absorb.