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| 183_notes:gravitation [2021/02/05 00:00] – [(More) Modern Gravitational Models] stumptyl | 183_notes:gravitation [2021/02/05 00:01] (current) – [Newton's 3rd Law] stumptyl |
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| The gravitational force provides the first example of [[http://en.wikipedia.org/wiki/Newton's_laws_of_motion#Newton.27s_third_law|Newton's 3rd Law]], which you might have heard colloquially as "For every action, there is an equal and opposite reaction." Unfortunately, [[http://www.wired.com/2013/10/a-closer-look-at-newtons-third-law/|this colloquialism is a terribly inaccurate definition]] that gets applied incorrectly quite often, [[http://scienceblogs.com/dotphysics/2010/05/06/mythbusters-energy-explanation/|even by the Mythbusters]]! | The gravitational force provides the first example of [[http://en.wikipedia.org/wiki/Newton's_laws_of_motion#Newton.27s_third_law|Newton's 3rd Law]], which you might have heard colloquially as "For every action, there is an equal and opposite reaction." Unfortunately, [[http://www.wired.com/2013/10/a-closer-look-at-newtons-third-law/|this colloquialism is a terribly inaccurate definition]] that gets applied incorrectly quite often, [[http://scienceblogs.com/dotphysics/2010/05/06/mythbusters-energy-explanation/|even by the Mythbusters]]! |
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| Newton's 3rd Law results from the idea that a [[:183_notes:momentum_principle#net_force|force quantifies the interaction between two objects]]. You can also think of it as an empirical fact, which stems from our definition of force. That is, __//we observe when one object exerts a force on another object, the second object exerts a force on the first object of the same size but opposite in direction.//__ | Newton's 3rd Law results from the idea that a [[:183_notes:momentum_principle#net_force|force quantifies the interaction between two objects]]. You can also think of it as an empirical fact, which stems from our definition of force. That is, **we observe when one object exerts a force on another object, the second object exerts a force on the first object of the same size but opposite in direction.** |
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| To be more concrete, you can think about the gravitational interaction between the Earth and the moon (shown in the figure below). The magnitude of these gravitational forces are the same (see the equation above), but the vector direction for each always points directly towards the other object. | To be more concrete, you can think about the gravitational interaction between the Earth and the moon (shown in the figure below). The magnitude of these gravitational forces are the same (see the equation above), but the vector direction for each always points directly towards the other object. |