by Reynold Conger

Created on: March 19, 2010

Sir Isaac Newton was one of those renaissance men who made contributions in a number of fields.  What separates him from the rest of the scholars of history is that so much of his teaching has endured with minimum change.

Before his time, no one understood gravity nor did anyone understand how and why objects moved.  Astronomers struggled with fantastic theories to explain the motion of planets and moons.  Galileo had to drop objects off the leaning tower of Piza to demonstrate that all objects accelerate at a constant rate in free fall regardless of weight.

Newton defined gravity as a force caused by the attraction of two objects.  In 1686 Newton introduced what became known as Newton's three laws of motion.  When these three laws are applied along with Newton's gravitational theory, almost all motion becomes systematic.  With the aid of a new form of mathematics, calculus, Newton was even able to make the calculation of orbits practical.  Everything in the universe follows Newton's three laws of motion.

1st law:  An object will stay at rest unless and until it is acted upon by an outside force.  When acted upon by an outside force, the objects accelerates in proportion to size of the force and in inverse proportion to the mass of the object.  In practical terms we use the equation F=ma where F is the force, m is the mass of the object and a is the acceleration that results.  Acceleration is defined as the rate of change of velocity with respect to time.  In calculus terms it is the derivative of velocity with respect to time.

The most obvious example of this is a golf ball.  It sits on the fairway without moving until the golfer hits it with his club.  The club applies a force to the ball and the ball accelerates.  It moves.  The harder it is hit, the faster it moves.

2nd law:  An object in motion will travel on a linear path with a constant velocity unless and until it is acted  upon by an outside force.  Again, the equation F=ma.  If the force directly opposes the path of the object, the resulting acceleration will slow or stop the object.  If the force is acting directly along the path of movement, the object will accelerate to a faster velocity.  As before, acceleration is defined as the rate of change of velocity with respect to time.  If the force acts at an angle to the path of the moving object, the object will change direction.

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