Newton's First Law of Motion

II. Galileo, Aristotle, and Inertia - Read this article and answer the questions on your notes sheet.

In his great text, Physica, Aristotle provides an explanation of motion. Objects have a natural place which they seek. For instance, objects made of wood, rock, and metal tend to seek out the Earth as that is their natural place to be. Objects made from air seek out the heavens and will tend to rise. This is natural motion. Violent motion would be something we do against an objects nature. So an exerted force will cause an object to move. Thus consider a ball rolling across the ground. It eventually comes to rest. Aristotle would have said since we are no longer rolling the ball, we are no longer exerting a violent action on it. Thus its natural place is to come to rest.

Galileo defined the concept of inertia. Galileo did not believe the ball came to a rest because it desired to be in its natural state. Inertia is the tendency of an object to maintain its state of motion. So the ball should roll on forever. The ball only stops rolling because an external force (friction) causes the ball to stop. The more inertia an object has, the harder it is to change its state of motion. An object's mass is simply a measure of its inertia. The more mass an object has, the more difficult it is to change its state of motion.

IV. Watch the short videos. Answer the questions on your notes sheet.

a. Pulling a tablecloth out without affecting the dishes:

b. Rolling a marble in a hoop:

c. Car accidents

Take the Google Quiz when done with the assignment.