Page:Popular Science Monthly Volume 9.djvu/38

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result are a variation in the mass of the hammer-head, and a variation in the length of the handle. By a varied mass there is a varied weight in the hammer; by a varied length of handle there will, with the same muscular effort, be a varied velocity in this mass, and upon a combination of mass and velocity depends the produced energy. Now, if a mass of metal, moving at a known velocity, strike an object, the energy of that blow results entirely from the conditions at the moment of impact. For example, the work in the hammer, H, as it strikes the nail, N (Fig. 20), does not depend upon its velocity through the arc,

PSM V09 D038 Physics of proper hammer use.jpg
Fig. 20.

Q N, but only upon the velocity when commencing contact with the nail. Hence, so long as the material which gives the blow and the mass of it are the same, it is not of any consequence how the velocity was accumulated. It may result from centrifugal or rectilinear action; it may result from muscular effort, or from steam-pressure, or from gravity.

It may now be obvious that, other elements remaining unchanged, whatever accelerates the velocity of a hammer increases, according to very clear rules, the energy or power of the same hammer. Hence the tendency of contrivances, as manifested in the addition to steam as well as handicraft hammers; for example, in the early lift-hammers,