Chap12UniversalGravitation - Physics 0 Universal...

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Physics Chapter 12 Universal Gravitation Study Notes Mr. Lin 1 0 Universal Gravitation a. Universal gravitation : Since the gravitational force is experienced by all matter in the universe, from the largest galaxies down to the smallest particles, it is often called universal gravitation . b. Gravity is the way in which masses communicate with each other . Every mass in the universe reaches out to attract every other one, and every mass feels an attraction from every other one. c. General theory of relativity : Gravity rises from the warping of space and time. General theory of relativity proposed in 1916 by Albert Einstein explained these differences and provided a geometric explanation for gravitational phenomena, holding that matter causes a curvature of the space-time framework in its immediate neighborhood. d. Examples: projectiles, satellite, planets, galaxies, and clusters of galaxies are all influenced by gravity. 1 The Falling Apple a. Galileo’s concept of inertia — without an outside force, moving objects continue to move at constant speed in a straight line. b. Newton’s first law of motion — An object continues in its state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by an outside unbalanced force . c. Isaac Newton’s concept of gravity — If an object undergoes a change in speed or direction, then a force is responsible. The falling apple changes its speed and the revolving moon changes its direction. Both changes require a force. Newton has the insight to see that the moon is falling toward Earth, just as the apple is. Both of them are pulled by Earth’s gravity . Newton didn’t discover the gravity but expanded Galileo’s concept of inertia and discovered that gravity is universal . 2 The Falling Moon a. The falling moon : The moon falls around Earth because it falls beneath the straight line it would follow if no force acted on it. The moon is simply a projectile circling Earth under the attraction of gravity . b. Newton’s cannon-ball illustration : The mountain top cannon is above Earth’s atmosphere, so that air resistance would not impede the motion of the cannonball. If it were fire faster, its path would be less curved and it would hit Earth farther away. If the cannonball were fired fast enough, its path would become a circle indefinitely. It would be in orbit. c.
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This note was uploaded on 11/18/2010 for the course CPHY 101 taught by Professor Jay during the Fall '10 term at University of Massachusetts Boston.

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Chap12UniversalGravitation - Physics 0 Universal...

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