THE PRINCIPLES OF
MODERN PHYSICS

Newton's Laws of Motion
In modern form

First Law (Inertia):

An object's velocity vector remains constant if and only if the net force acting on the object is zero.

Second Law (Force and Momentum):

A force applied on an object equals the rate of change in its momentum with time.

ΣFx = max

where F = force, m = mass, and a = acceleration. (note: this mathematical formula was not written by Newton)

Third Law (action-reaction):

In an interaction between two objects, each object exerts a force on the other. These two forces are equal in magnitude and opposite in direction

Law of Gravity

Any two objects exert gravitational forces on each other that are proportional to the masses of the two objects and inversely proportional to the square of the distance between their centers.

F = Gm1m2/r2

where F = force, G = universal gravitational force (a constant value estimated at: 6.674 × 10-11 N.m2/kg2), m = mass of the object, and r = the distance between the centers of the two objects.


Isaac Newton
1643 - 1727

Born in England, this philosopher is most famous for writing what has become known as the three laws of motion, in his book Philosophiae Naturalis Principia Mathematica, written in Latin (the language of science at the time) and published in 1687. He was not only a natural philosopher (physicist), but also a mathematician, an astronomer, an alchemist, an economist, and, most importantly, a theologian. Newton wrote more about religion than anything else.

Other interesting facts about Newton: He was a Unitarian Christian (one who does not believe in the Trinity), a high school dropout, and an honest man. He gave credit to his predecessors when formulating his laws of motion, stating: "If I have seen farther, it is because I was standing on the shoulders of giants," in reference to Galileo (1564 - 1642) and René Descartes (1596 - 1650).


Sources used:

  • Giambattista, A., et al.. (2010). College Physics.