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# Three universal laws of motion – Isaac Newton (1643-1727)

Sir Isaac Newton

Newton’s Laws of Motion were first published in his work Philosophiae Naturalis Principia Mathematica (1687). Newton used them to prove many results concerning the motion of physical objects. In the third volume (of the text), he showed how, combined with his law of universal gravitation, the laws of motion would explain Kepler’s laws of planetary motion.

• 1 Newton’s First Law: Law of Inertia –

Lex I: Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum mutare.

"An object at rest or traveling in uniform motion will remain at rest or traveling in uniform motion unless acted upon by a net force."

• 2 Newton’s second law: Law of Motion –

Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimtur.

"The rate of change of momentum of a body is equal to the resultant force acting on the body and is in the same direction."

• 3 Newton’s third law: law of reciprocal actions –

Lex III: Actioni contrariam semper et aequalem esse reactionem: sive corporum duorum actiones is se mutuo semper esse aequales et in partes contrarias dirigi.

"All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction."