(1) The gravity of the earth to the moon is not only related to the mass of the moon, but also related to the square of the mass and distance of the earth. (2) The formula of universal gravitation is F=kMm divided by the square of r, and f = 4 π 2mr/t 2. The two sides can compare as soon as possible and invite Xiao M. In addition to F∝m and Newton's third law, Kepler's third law T 2/R 3 = K (K is a constant) is also deduced.

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