The three laws are:

First law: The velocity of a body remains constant unless the body is acted upon by an external force.

Second law: The acceleration a of a body is parallel[disambiguation needed ] and directly proportional to the net force F and inversely proportional to the mass m, i.e., F = ma.

Third law: The mutual forces of action and reaction between two bodies are equal, opposite and collinear.

The first law had already been formulated by some philosophers prior to Newton, unusually, Hobbes (not generally taken to be interested in physical phenomena in themselves) said in the Leviathan '...[the proposition] that when a thing is in motion it will eternally be in motion unless somewhat else stay it, though the reason be the same (namely that nothing can change itself)...', given his reasoning, I think it safe to mean constant speed and direction, otherwise change is occuring and he explicitly rules that out. I think the same proposition is mentioned in Lucretious's De Rerum Natura.

Are there any antecedents for the second and third law, in either the scientific or philosophical literature?

I know that Hooke asked Newton to confirm that an inverse square law directed towards the Sun acting on the Earth would result in Elliptical motion. Though I don't have a reference for this, it leads one to suggest that Hooke understood the import of the second law.

This just leaves the Third Law.


Can't say I like the 3 laws as you state them - the 3 laws as I know them to be:

  1. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

  2. The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. The direction of propagation is equal to the direction of the sum of the forces applied to it.

  3. To every action there is an equal and opposite reaction.

Now, it is easier to see how we can apply the same logic to more metaphysical theory.

  1. People need a carrot or a stick to do anything. There has to be a reason that is in some way beneficial to that person (even if it is transferred).They will keep doing what works for them until a bigger carrot or stick causes them to change.

  2. People will always attempt to take the easiest path for the same reward (or avoidance of punishment). The more effort made, the greater the satisfaction or disappointment.

  3. Cause and affect.

By the way Hooke was a great mathmatician and scientist - the equal of Newton (and there were many arguements of plagurism and lack of credit against Newton for his gravity work as well as on light/optics). It was Newton as President of the Royal Society after Hooke's death that did everything to push his name from history - even going so far as to destroy his portrait which hung alonside those of other founding members).

  • NIce try. I like numero uno. Jun 16 '12 at 23:23

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