Newton’s First Law of Motion Inertia Chapter 3 Notes Newton’s First Law of Motion Inertia

3.1 Aristotle on Motion Aristotle (384 – 322 B.C.) It was natural to think that the natural state of all objects was to be at rest. Aristotle, the formost Greek scientist , studied motion and divided it into two types: natural motion and violent motion. Chapter 9

3.1 Aristotle on Motion Natural Motion Straight up or down Circular Rock Smoke Circular Moon Stars Did not require force Chapter 9

3.1 Aristotle on Motion Violent Motion = Imposed motion The result of forces (push or pull) External cause Object in their natural resting place could not move by themselves : they had to be pushed or pulled. Chapter 9

3.2 Copernicus and the Moving Earth Nicolaus Copernicus (1473 – 1543) Copernicus reasoned that the simplest way to interpret astronomical observations was to assume that the Earth and other planets move around the sun. Chapter 9

3.3 Galileo on Motion Galileo Galilei (1564 – 1642) Supported Copernicus Force was not necessary for motion Friction is the force that acts between materials that touch as they move past each other. Chapter 9

3.3 Galileo on Motion Galileo argued that only when friction is present-as it usually is-is a force needed to keep an object moving. Rolling Balls on tilted surfaces If friction were entirely absent, a ball moving horizontally would move forever. Chapter 9

3.3 Galileo on Motion In the absense of friction, the moving ball would naturally keep moving. Galileo stated that this tendency of a moving body to keep moving is natural and that every material object resists change to its state of motion. The property of a body to resist changes to its state of motion is called inertia. Chapter 9

3.3 Galileo on Motion Roman Catholic Church Chapter 9

3.4 Newton’s Law of Inertia Sir Isaac Newton (1642-1727) Principia Mathematica Philosophiae Naturalis Knighted by Queen Anne in 1705 Chapter 9

3.4 Newton’s Law of Inertia Newton’s First Law – The law of inertia Restating Galileo Newton’s first law states that every object continues in a state of rest, or of uniform speed in a straight line, unless acted on by a nonzero net force. Things keep on keeping on. Demo Chapter 9

3.5 – Mass-A Measure of Inertia The more mass an object has the greater its inertia and the more force it takes to change its state of motion. Mass vs. Volume Kilogram (kg) – the fundamental unit of Mass Mass vs. Weight Chapter 9

3.5 – Mass-A Measure of Inertia Mass is the quantity of matter in an object. Mass is a measure of the inertia that an object exhibits. Weight is the force of gravity acting on an object. Chapter 9

3.5 – Mass-A Measure of Inertia 1 kg ≈ 2.2 lbs (approximately equal to) Weight is a force. The standard unit of force is the Newton (N). 1N ≈ ¼ lb 1 kg weighs 10 (9.8 really) Newtons. Chapter 9

3.6 The Moving Earth Again Earth in space 30 km/s Bird catches worm Cart & Ball Demonstration The law of inertia states that objects in motion remain in motion if no unbalanced forces act on them. Chapter 9