Some objects fall faster because of air resistance, which acts in the direction of motion of the object and exerts more force on objects with more surface area.Some objects fall faster because of air resistance, which acts in the direction opposite the motion of the object and exerts more force on objects with less surface area.Some objects fall faster because of air resistance, which acts in the direction of the motion of the object and exerts more force on objects with less surface area.Why do some objects fall faster than others near the surface of the earth if all mass is attracted equally by the force of gravity? This attraction is illustrated by Figure 7.9. The force is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. Expressed in modern language, Newton’s universal law of gravitation states that every object in the universe attracts every other object with a force that is directed along a line joining them. It is always attractive, and it depends only on the masses involved and the distance between them. The gravitational force is relatively simple. Scientists still expect underlying simplicity to emerge from their ongoing inquiries into nature. Great importance is attached to it because Newton’s universal law of gravitation and his laws of motion answered very old questions about nature and gave tremendous support to the notion of underlying simplicity and unity in nature. A more probable account is that he was walking through an orchard and wondered why all the apples fell in the same direction with the same acceleration. It had been known for some time that moons, planets, and comets follow such paths, but no one had been able to propose an explanation of the mechanism that caused them to follow these paths and not others.įigure 7.8 The popular legend that Newton suddenly discovered the law of universal gravitation when an apple fell from a tree and hit him on the head has an element of truth in it. This theoretical prediction was a major triumph. But Newton was the first to propose an exact mathematical form and to use that form to show that the motion of heavenly bodies should be conic sections-circles, ellipses, parabolas, and hyperbolas. Some of Newton’s contemporaries, such as Robert Hooke, Christopher Wren, and Edmund Halley, had also made some progress toward understanding gravitation. His forerunner, Galileo Galilei, had contended that falling bodies and planetary motions had the same cause. But Newton was not the first to suspect that the same force caused both our weight and the motion of planets. Sir Isaac Newton was the first scientist to precisely define the gravitational force, and to show that it could explain both falling bodies and astronomical motions. Concepts Related to Newton’s Law of Universal Gravitation
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