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| Galileo's Observation and Origin of Newtonian Mechanics |
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| Aristotle and other medieval thinkers believed that the natural state of bodies is the state of rest. Galileo opposed this concept. |
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| Galileo observed that, when a ball was made to roll down an inclined plane, its speed increased. |
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| An Object Moving Down an Inclined Plane with Increasing Speed |
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| Similarly, when it was made to roll up the inclined plane, its speed decreased. |
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| An Object Moving Upward with Decreasing Speed |
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| He then tried rolling it on a horizantal plane. Galileo repeated this experiment by making the surface very smooth. He observed that the ball continued to move for a longer time. Galileo suggested that the speed of the ball moving on a horizontal plane would remain constant in the absence of an external force or force of friction. |
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| Galileo suggested that the natural tendency of all bodies is to oppose a change in their state of rest or motion. |
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| An Object Moving Along a Horizontal Plane |
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