Isaac Newton (1643-1727)

Overview

Isaac Newton is considered by many to be the father of modern physics. He invented calculus, and with calculus in hand, people could create mathematical models of changing systems. His three laws of motion and his law of gravitation, however, are still one of the first things that all physics students learn, and are still the backbone supporting a lot of physics that is done today.

Laws of Motion

Newton's Laws of Motion are still used by physicists all over the world. Newtonian Physics is taught in many courses at the college level, as well as high school and middle school. All of mechanics is based upon these three laws:

1. Every object has uniform motion unless acted upon by a force.
2. The force on an object is equal to the object's mass times the resulting acceleration:
3. For every action, there is an equal and opposite reaction.

These laws are used to describe everything from throwing a ball to the merging of galaxies. Even though it has been shown by people like Albert Einstein (father of relativity) and Erwin Schrödinger (father of quantum mechanics) that Newton's Laws are really just approximations of the real world, they work so well on a wide range of scales - especially the ones that govern our day-to-day lives - that they are still used in lieu of the better laws. For example, you would use Newtonian Mechanics to describe the acceleration of a car, not Einstein's General Relativity.

Law of Gravity

Newton's Law of Gravity is not precise in extreme circumstances, such as very high velocities, very strong gravity fields, or at very small scales*. For cases such as these, Einstein's General and Special Relativity theories, or Schrödinger's Wave equation are needed. However, in most other cases, and especially those with which we are familiar with on Earth, Newton's Law works extremely well.

It is based upon his laws of motion, and it shows that and describes the manner in which two objects exhibit a force upon the other. It is the equation to the left of this paragraph. It says that the gravitational force experienced is equal to a gravitational constant times both masses divided by the distance between them squared.

The value "G" is an extremely small number, and therefore the gravitational force is extremely weak - the weakest of the four fundamental forces. Its current experimental value (as of 2000) is 6.67390*10-11±0.0014%, where the units are m3/kg/s2.

This law also shows that the force of gravity dies off with the square of the distance. This means that if you are twice as far away from something, then the gravitational force you experience from it (and the force it would experience from you) is 1/4 as much.

*Newton's Law of Gravity has been accurately tested and measured on scales on the order of a millimeter.