Newton's Three Laws

Newton’s three laws are fundamental laws of physics.  You cannot be too familiar with these laws.  The next several lectures will build on one another, and lead us to an understanding of many phenomena observed around us in everyday life. Since a force results in a change in a object’s motion, we can see that a study of forces (dynamics) is inextricably related to a study of motion (kinematics). Also, since a force is a vector quantity, it can be easily seen that our study of forces and Newton’s laws will apply all of  the expertise that we have been developing so far this semester.

We summarize Newton’s three laws in the table below. You should learn these laws verbatim, and understand their meanings and consequences.  (It wouldn’t be a bad idea to review the discussions in Lecture 5 at this point....)

1st Law

An object moving with constant velocity will continue to move with constant velocity until acted upon by a net, external force.

 

2nd Law

The net external force acting on an object is equal in magnitude and direction to the product of that object’s mass and its acceleration:

L8_01

 

3rd Law

The force exerted by one object A on a second object B is equal in magnitude but opposite in direction to the force exerted by the second object B on the first object A:

L8_02

The next section discusses some of the meanings and consequences of these important laws.