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Why are Newton's laws called universal laws even though Newton's are not applicable to...

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dananagoud | Student, Grade 9 | eNoter

Posted July 28, 2012 at 12:45 PM via web

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Why are Newton's laws called universal laws even though Newton's are not applicable to all substances?

When a ball hits the wall & comes back it is not an example for Newton's 3rd law of motion.

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bandmanjoe | Middle School Teacher | (Level 1) Senior Educator

Posted July 28, 2012 at 5:25 PM (Answer #1)

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Well, when you call something "universal", you are covering everything that is involved in that aspect under the sun.  The thing I have noticed in this regard is there are always exceptions to the rule, there is hardly anything where one rule applies to everything.  People would be better by prefacing these rules with "Generally", which leaves room for the exceptions to the rule.  That being said, how can you say a ball bouncing off a wall is not an example of Newtons third law of motion?  The law states "For every action force, there is an equal and opposite reaction force".  The ball hits the wall with an amount of force, generated by the product of its mass times its acceleration (Newtons 2nd law of motion).  The wall responds by pushing back on the ball with a force that is equal to that exerted by the ball.  Otherwise, the ball would keep on going through the wall in the direction it was traveling (Newtons 1st law of motion).  The ball bounces back and away from the wall as a result.  That is Newtons 3rd law of motion in action.

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