Text-book of human physiology : including histology and microscopical anatomy with especial reference to the practice of medicine / by L. Landois.

  • Landois, L. (Leonard), 1837-1902.
Date:
[1904], ©1904
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of human physiology : including histology and microscopical anatomy with especial reference to the practice of medicine / by L. Landois. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    of force. This force diminishes inversely as tlie square of the distance between the two bodies. The power of attraction is further directly proportional to the quantity of the attracting matter, though without any relation to the quality of the body. The intensity of the force of gravitation can be measured by the extent of the movement that it communicates to a freely falling body previously supported in a vacuum but deprived of its support. This figure is 9.809, because the force of gravity operating for one second upon the freely falling body imparts to this a velocity of 9.809 meters. The final velocity of the freely falUng body at the end of the first second (deter- mined experimentally) is designated thus, g ^ 9.809 meters. The velocity, v, of the freely falling bod\' is in general proportional to the time, t, occupied in falling. Therefore v = gt (i), that is, at the end of the first second v = g, i = g = 9.809 meters. The distance through which the body falls, s := -1- (2); that is, the 2 distance through which a body falls is as the square of the time occupied in falling. From (i) and (2) there follows (by eliminating t) v = y'^gs (3). The velocity is as the square root of the distance traversed in falling, thus —- = s (4) A freely falling body, and also in general every mass in movement, possesses kinetic energy (actual energy); it is to a certain degree a reposi- tory of force. The kinetic energy of a body in movement is always equal to the product of its weight (determinable by scales) and the height to which it would rise from earth if it were raised from the earth with the velocity peculiar to it. If the kinetic energy of the moving body be designated W and its weight P. then W = P, s; then, from (4), W = P— (5). The kinetic energy of a body is therefore proportional to the square of its velocity. If an accelerating force operating on a body (pressure, traction, or tension) drives it for some distance in the direction of its activity, the force thus expends work. This is equal to the product that is obtained if the amount of pressure or traction that propels the body is multiplied by the length of the path traversed. If K represents the pressure or the traction with which the force operates upon the body and S the path, then the work A = KS. In the same way the attraction between the earth and a body raised above it (as, for instance, a ram) is a source of work. It is customary to express the value of K in kilograms, but, on the other hand, that of S in meters. Accordingly the unit of work is the kilogrammeter (according to some the grammeter), that is, the force that is capable of raising i kilo (according to some i gram) to the height of I meter. Potential Energy.—Transformation of Potential Energy into Kinetic Energy, and the Reverse.—In addition to the kinetic energy referred to, bodies may possess also mechanical potential energy. By this designation is understood an aggregation of forces that are still inhibited in their free evolution, and that, further, are causes of movement, without