GRAVITATION

is the attraction which bodies have for one another due to their ma . Newton formulated the Law of G. thus: ‘the force of the attraction which bodies have for one another is directly proportionate to their ma es, and inversely proportionate to the square of their distances apart.’ This is the most general property of matter, and no exceptions to Newton’s Law are known. - If a body is thrown up into the air, it - falls to the earth after a longer or shorter period of time, depending upon the greatne of the force opposed to that of gravity. Such a body has a certain attraction for the earth, but since the ma of the earth must nece arily be larger than that of any body on it, the force with which the body attracts the earth must be negligible compared to. that with.which the earth attracts the body. When the force impelling the _ body to move upwards is expended, the pull of the earth on the body becomes evident. The value of gravity is 32:2 ' ft. per sec., and it is unaffected by the nature of the matter. The value of gravity is le at the equator than at the poles, but this does not affect ordinary calculations. By very exact ex_ periment the force of attraction which a body exerts on the earth can be determined. Through the force of g. the sun and various other planets affect the earth, while the earth affects the moon, acting through a distance of 240,000 miles, - The mutual attraction between a body and the earth is represented by its weight. The presence of large ma es, such as mountains, does not alter the weight of any substance for practical purposes. Weight always acts downwards through the center of gravity, (t.e.) the point _ through which the resultant of all the forces due to gravity must pa . When 2 body is lifted a certain resistance is felt. This resistance is the force with ‘which the body is attracted to the earth. Water flowing from a horizontal hose gradually curves towards the earth as the force by which it is expelled horizontally becomes exhausted, and ‘gravity becomes noticeable. A drop of water as it falls towards the ground soon loses its spherical shape and becomes pointed, due to the attraction of the earth on the surface nearest it. See Reiativiry, THEORY OF.