History of Laws of Motion

1. History of Laws of Motion

2. Aristotle ~ 350 B.C. • He believed that the natural state for all objects was at rest. • He believed all motion was caused by a force. If the force stopped, the object would eventually stop.

3. Aristotle was WRONG!!! • Many people still think along the lines of Aristotle. • Objects do not “want” to be at rest. • If we can remove friction, objects will not stop. • On Earth, a completely frictionless surface is impossible.

4. Galileo ~ 1600 • Galileo argued that a moving object would move forever, without friction. • He also argued that objects naturally resist CHANGE in motion. • He called this inertia.

5. Inertia • Inertia — an object’s resistance to change in motion. • NOT just an object’s resistance to stopping, but also to slowing down and speeding up. • Inertia is measured by its mass. • The more mass, the more an object will resist a change in motion.

6. Sir Isaac Newton 1642-1727 • Developed and explained three laws to explain how objects move. • He also explained other concepts including gravity and calculus.

7. Newton’s First Law of Motion • An object at rest tends to stay at rest, and an object in motion tends to stay in motion in a straight line at a constant speed unless it is acted on by a net outside force. • An object is going to keep on doing what it is already doing unless something comes along and pushes it.

8. Examples • How can a magician pull a tablecloth out from under a stack of plates? • The plates have inertia; they will not move unless a force is applied to them. • Why do you need to wear a seatbelt? • You have inertia. When moving, you will continue moving at the same speed until an outside force stops you.