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sir isaac newton, the first person who studied gravity seriously, discovered what is known as the law of universal gravitation. it defines the amount of attraction of one particle of matter on another particle of matter. the formula for figuring the amount of attraction, or gravitational force, is written in the following way: the formula means that first you multiply the constant of the gravitational pull between particles, g, by the mass of particle 1, m1, and the mass of particle 2, m2. then you divide the answer by the square of the distance between them, d2. this equation will give you the amount of pull or force between the two particles. it may seem reasonable to question the law of universal gravitation because newton wrote it during the seventeenth century. however, modern scientists have tested it using modern and innovative scientific equipment and increased knowledge of the solar system. the formula remains true today.

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