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Amendment to Newton 1

  1. Mar 25, 2004 #1
    Newton’s first law was actually Galilean idea. It was Galileo who first thought that once we succeed eliminating all the friction from the surface one object slides on the object would slide forever. Newton had only royal style of putting it: “Subjected to no force the object will preserve its uniform motion i.e. travel with constant speedâ€. But there is a catch. Galileo didn’t have the entire force - picture in sight. Newton, later, in his third law stated that for every action force there is an equal and opposite reaction force. In the case of the sliding object the friction is only the reaction the object gets from the surface meaning that the action must come from its motion. Thereby, eliminating the friction from the surface would eliminate the motion of the object. My amendment to Newton’s first law would be: “Subjected to no force the object will perform no motionâ€. Even in this improved version, Newton’s first law is only a trivial case of one other more general law. That general law states: “The displacement always takes the direction of the force causing itâ€. You might not like it because it comes from me, you might not like it because of the way I put it, but rest ashore; you obey this law all the time.
  2. jcsd
  3. Mar 25, 2004 #2

    Doc Al

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    Staff: Mentor

    Apparently you do not understand Newton's laws.
  4. Mar 25, 2004 #3
    You've got the two confused. Friction is not the action force, it's the reaction force. Friction is not pushing the object by providing resistance, it is providing resistance to the object which is pushing against it. In order for friction to exist, the force must already have been applied to the object creating the friction. Proof of this is in the fact that space travel is possible.
  5. Mar 25, 2004 #4
    I do in fact like the way you put it. You have certainly made my day.
  6. Mar 25, 2004 #5

    Doc Al

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    Staff: Mentor

    Don't confuse Action/Reaction pairs (as in Newton's 3rd law) with cause and effect. Per Newton, when objects interact they always exert forces on each other in matched pairs: A on B and B on A. These are the action/reaction pairs. As to which force is the action, and which the reaction: that is totally arbitrary.

    For an object sliding along a surface with friction, I see three forces acting on the object. I will list them along with the reaction force for each:

    (1) Weight (earth pulling on object); reaction force: object pulls on earth.

    (2) Normal force (surface pushes up on object); reaction force: object pushes down on surface.

    (3) Friction (surface pushes on object, parallel to surface); reaction force: object pushes on surface, parallel to surface.
  7. Mar 27, 2004 #6
    Couldn't have done it without making Doc Al's night. :biggrin:
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