(Newton's Law of Motion) Brett Morrow

Issac Newton's Three Laws of Motion changed our understanding of the basis of classical mechanics."They desribe the relationship between the forces acting on a body and it's motion due to those forces". The first law states that every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied. This means that in the nonexistence of a non-zero net force, the focus of mass of a body either remains at rest, or moves at a continuous velocity. The second law states that the relationship between an objects mass (m), it's acceleration (a), and the applied force (F) F=ma. "The property a body has of resisting any change in its state of rest or of uniform motion in a straight line is called inertia. the inertia of a body is related to what can be loosely thought of as the "amount of matter" it contains. A quantitative measure of inertia is mass: the more mass a body has, the less its acceleration when a net force acts on it". The third law states that for every action there is an equal and opposite reaction. The law is sometimes referred to as action-reaction law. Action and Reaction forces never balance out because they act on different bodies. "The first law of motion is included in the second, since a body is not accelerated when there is no net force acting on it and it must therefore remain at rest or in motion at constant velocity. the second and third laws of motion are independent of each other".

History of Newton's Law of Motion

In the sixteenth century, Copernicus proposed that Earth and other planets orbited the Sun, but his theory contained no physics. It did not say why the planets should orbit the Sun. Galileo Galilei was the next to challenge the Greek philosopher's ideas. Galileo presented two common experiments that set the tone and meaning for all scientific work that would follow. But Galileo found that the two objects fell at the same rate and struck the ground roughly at the same time. Galilao was criticized by the Catholic Church and forced to withdraw his belief in the Copernican model. He then realized that to eventually win the Copernican model he needed a physical source. Galileo then started to develop the new physics needed to explain universal motions. Isaac Newton, who was born the year Galileo died, was built on the groundwork laid by Galileo. The result, Newton's laws, was an impressive creation that for the first time explained motions both on Earth and in the universes with a united set of laws.

Application of Newton's Law of Motion

An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
The principle behind this law is simple: if an object is moving along a path at a certain speed it will remain along this track until another force acts upon it. The rocket is at rest when it is on the launch pad, and when the trigger is pulled the rocket is propelled skyward. Several forces are acting upon it, including gravity and friction. The rockets and space shuttles have great mass, Newton's 2nd Law tells scientists that they must produce rockets that will have enough force to launch the spacecraft into orbit. The more mass that needs to be lifted, the more force they must apply to break through gravity’s pull.


  1. http://en.wikipedia.org/wiki/Newton's_laws_of_motion
  2. http://csep10.phys.utk.edu/astr161/lect/history/newton3laws.html
  3. Physical Science special edition CH.3 pg. 18

This WikiPage developed by (Brett Morrow, Summer 2011)