Lesson 4 Inertia

Inertia encompasses the concept that any object moves at a constant speed in a straight line unless acted upon by an outside force. This concept was developed by Galileo Galilei. After his birth in 1564, Galileo developed the Law of Falling Bodies and experimented with inclined planes. Galileo did not cease his experimentation, but instead developed two telescopes, which were the source of his financial security throughout his life. Through these telescopes Galileo discovered the moons of Jupiter (Galilean satelites), the mountains on the surface of the moon, the phases of venus, and the black spots present on the sun. Through his studies of our solar system, Galileo confirmed that Earth, and the other planets in our solar system spin as they complete revolutions around the sun. Capurnicus's model of our solar system was in fact correct, however, this assertion did not explain why the inhabitants of the Earth do not feel as though they are moving as the Earth orbits around the sun.

Aristotle originally believed that all objects come to rest naturally but Galileo concluded, based upon the principle of inertia, that everything is in horizontal motion at the same speed and time as the Earth. Thus, humans do not feel as though they are in motion because there is no friction due to the force of gravity. From this enlightenment, Descartes developed the Law of Inertia and concluded that objects in motion remain in motion until something interferes. The universe is an example of an object that will never come to rest because absolute rest and motion do not exist.

Furthermore, whether an object is in motion or at rest completely depends on view point for all motion is relative.

In order to understand the principle of inertia, Galilieo said to picture a ball falling from the mast of a sailboat. If the sailboat is moving, the ball won't fall back into the water but will fall straight down on to the deck of the ship. On the other hand, if the ball was sitting at rest of the mast of another sailboat and then released while the other sailboat is in motion, the ball will fall back into the water. This is because objects fall in a parabolic curve. The principle of relative motion and inertia is displayed in the following video:



Without the classification of the idea of inertia, Newton would have never been able to compose his laws of mechanics.