# Gravity - Todays New York Times Motion of a car Consider...

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Today’s New York Times

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Motion of a car Consider all of the forces acting in this situation As the tire moves over the road, the tire flattens. The force exerted by the road on the tire acts to slow the tire’s rotation. Rolling resistance Less pronounced for steel wheels gravity normal force air resistance

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Gravitation Remember the story about Isaac Newton and the apple Maybe it didn’t happen in reality, but the reasoning is roughly correct Newton had the insight to realize that the force between the Earth and the apple is the same as the force between the Earth and the Moon
Gravitation The apple falls to the ground with an acceleration of 9.8 m/ s 2 The Moon falls away from the straight line path it would follow if there were no forces acting on it remember Newton’s first law Isaac Newton compared the measurements for the Moon’s acceleration to his calculations and found they didn’t agree so he put his theory away for 20 years, and worked on optics

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Gravitation Inspired by the appearance of Halley’s comet in 1682, he returned to the problem and found errors in the experimental data Now the data agreed with his predictions He then published the universal law of gravitation
What did he find? He found the acceleration of the moon to be ~2.7X10 -3 m/s 2 Radius of Earth =6.37X10 6 m Average Earth-Moon distance is 3.84X10 8 m So the Moon is about 60 times as far away from the center of the Earth as is someone standing on the surface of the Earth The acceleration due to gravity decreases as the square of the distance from the center of the Earth 9.83 m / s 2 2.7 X 10 3 m / s 2 3600 = 60 2 video

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Universal law of gravitation Incredibly simple and beautiful relation The gravitational force between two masses is proportional to the product of the two masses and is inversely proportional to the square of the distance between them Before we dealt with mass in the equation below, technically known as the inertial mass Here we are dealing with
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Gravity - Todays New York Times Motion of a car Consider...

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