Acceleration

[Lat. acceleratio, hastening; Fr. acceleration.] The act of accelerating; a hastening. (Mech.) The motion of a moving body, when its velocity is continually increasing. With whatever velocity a falling body moves in the first second, it will, at the end of two seconds, move with twice that velocity, and so on; the force of gravity increasing as the body approaches the earth. This is, however, not mathematically true, as a little time is lost through the increased density and consequent resistance of the air at each moment. Acceleration of the stars. A term applied in ancient astronomy to the time by which the fixed stars anticipate the diurnal motion of the earth. Acceleration of the moon, is the increase of the moon's mean motion from the sun, compared with the diurnal motion of the earth, which is calculated at about ten seconds in a century. Acceleration and retardation of the tides , are certain irregularities between the times of high water, which difference would be constant supposing the tides occurred at regular intervals. The tides are caused by the attractions exercised by the sun and moon on the waters of the earth. The earth being nearer to the moon than to the sun, it is by her that the greatest influence is pro duced. The moon takes 24 h. 50 m. to perform one revolution round the earth; high water ought, therefore, to arrive at exact intervals of 12 h. 25 m. This interval is, however, continually changing at different times and places, being influenced by three principal causes: - the relative distances of the sun and moon, of the earth and moon, and the moon's distance from the equator. Local circumstances, such as currents, prevailing winds, ., are other causes of these irregularities.