# What in Newtons three laws of motion original to himself and not a paraphrasing of his predecssors

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, Hobbes 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?

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The third law is the original one. The rest are known to contemporaries, although not to philosophers, rather to the scientists. You can see Hooke uses the first and second laws along with Kepler's third law to deduce that gravity is inverse square. –  Ron Maimon Jun 13 '12 at 4:40
Thats interesting. I would've suspected the second law to be the original one. Are you saying Hooke was the originator of the second law and the notion of Force? As for the third, isn't there some notion of universal balance (within the philosophical literature), where every action on the moral plane is countered by an opposite one? I'm guessing here, and hope some-one can correct and edify me here. One expects there is more to the story of Gravity than Newton, as far as I remember Hooke approached Newton to ask whether he could prove that an inverse law gives elliptical motion. –  Mozibur Ullah Jun 13 '12 at 4:51
But does this mean that the notion of Gravity as a force pulling the Earth towards the Sun also originated with Hooke, or were others involved? –  Mozibur Ullah Jun 13 '12 at 4:56
The second law was just common knowledge, as was the first. It probably is due to Galileo and contemporaries, although it took a while to be codified. The laws of motion are not the point of the Principia, they are just the intro. The main point are the special problems. Hooke certainly understood them. Hooke came up with the inverse square law independently of Newton (and before Newton published), and it was pressure from Hooke that led Newton to publish the Principia. Hooke couldn't see that the orbits in an inverse square law would be ellipses, something which Newton had already worked out. –  Ron Maimon Jun 13 '12 at 7:55