A Basic Explanation of Newton's Three Laws of Motion

By Kathy Foust

Use this basic guide to help you to understand Newton's three Laws of Motion. You'll find simple and easy to follow explanations for each concept.

Sir Isaac Newton (1642-1727) was one the most prominent scientists of all time. Without his laws and formulas, the technology of today would not be possible because we would not know how to develop it, measure it or use it. Airplanes would forever be grounded because the idea of thrust would not be possible. Automobiles would never exist because we would not know how to compute the amount of force needed to move them. Below you'll find Newton's three Laws of Motion listed and explained for your convenience.

Newton's First Law of Motion

Newton's First Law of Motion states that an object will remain at rest or in uniform motion in a straight line unless acted on by an external, unbalanced force.

Before Newton, there was Galileo. Galileo stated that objects would naturally remain in motion rather than coming to rest. In other words, every moving object would have to be stopped by an external force. Newton used this idea in his own laws. This idea was contrary to even earlier conceptions by Aristotle that every object required a force to remain in motion. In other words, Aristotle believed that objects were naturally without motion unless acted on by outside forces, with the exception of celestial bodies. Obviously, gravity has a lot to do with the laws of motion and in Aristotle's time, the laws of gravity had yet to be written, so his assumption was a sign of the times rather than a sign of lack of Aristotle's brilliance.

Newton's Second Law of Motion

Newton's Second Law of Motion states that If an external, unbalanced force is required to produce a change in velocity, then an external unbalanced force causes an acceleration. Or more simply put, force = mass x acceleration.

Acceleration created by an unbalanced force on the mass of an object is proportional to the magnitude of the force and in the direction of the force. So, if the object's mass has more force than the external unbalanced force, there will be no motion. Also, the larger the mass of the object, the smaller the acceleration.

Put simply, the force on the object must be stronger than the mass of the object itself to create acceleration and even then, the acceleration is dependent on the mass of the object, as well as the unbalanced external force.

Newton's Third Law of Motion

Newton's Third Law of Motion states that for every every action there is an equal and opposite reaction. Or action = opposite reaction.

If an object is pushed on with enough force, the object will respond by moving with just as much force. Consider a baseball game. When the batter swings the bat, he (hopefully) hits the ball with enough force to reverse the motion of the ball and send it flying! This is Newton's Third Law of Motion in action.