Chapter 3 Newton's First Law of Motion ~ InertiaForces cause change in motion.

Objectives

0Describe Aristole's concept of motion.0Describe Copernicus' idea about Earth's motion.0Describe Gallileo's idea about when force is needed to

keep an object moving.0State Newton's firs law of motion. 0Descibe the relationship between mass and inertia.0Explain how the law of inertia applies to objects in

motion.

Key Terms

0Friction [P.30] is the name given to the force that acts between materials that touch as they move past each other.

0 Inertia [P. 32] is the property of a body to resist change to it state of motion.

0Newton's Firs Law [P. 33] usually called law of inertia, is a restatement of Galileo's idea that a force is not needed to keep an object moving.

Key Terms

0Law of Inertia [P.33] 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.

0Kilograms [P. 36]  Mass is measured in the unit of kilograms.

0Mass [P. 37] is the quantity of matter in an object andis a measure of the inertia that an object exhibits in response to any effort made to start it, stop it , or otherwise change its state of motion.

Key Terms

0Weight [P. 37] is the force of gravity on an object.  ( Mass and weight are not the same but proportional to each other in a given place.)

0Newton [P. 38] The SI unit of Force is the newton.

3.1 Aristotle on Motion

0Aristotle, the foremost Greek scientist, studied motion and divided it into two types: natural motion and violent motion.

0During Aristotle's time, natural motion on Earth was thought to be either straight up or straight down: It was "natural" for heavy things to fall and for very light things to rise.

3.1 Aristotle on Motion

0Violent motion was imposed motion and it was the result of forces that pushed or pulled.

0The proper state of objects was thought to be one of res, unless they were being pushed or pulled or wer moving toward their natural resting place.

3.2 Copernicus and the Moving Earth

0Cpoernicus reasoned that the simplest way to interpret astronomical observations was to assume that Earth and the other planets move around the sun.

0Copernius' idea of motion in space was extremely controversial at the time, because most people believed the Earth was at the center of the universe.

0Copernicus worked on his ideas in secret to escape persecution.  At the urging of his close friends, he publiched his ideas.

3.3 Galileo on Motion

0Galileo argued that only when friction is present-as it usually is - is a force needed to keep an object moving.

0One of Galileo's greatest contributions to physics was demolishing the notion that a force is necessary to keep an object moving. A force is any push or pull.

0Friction is the force that acts between materials that touch as they move past each other.

3.3 Galileo on Motion

0Galileo found that a ball rolling on a smooth horizontal plane has almost constant velocity, and if friction were entirely absent, the ball would move forever. Gaileo also stated that the tendency of  a moving body to keep moving is natural and that every object resists change to its state of motion.

0The property of a body to resist changes to its state of motion is called inertia.

3.4 Newton's Law of Inertia

0Newton'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.

0 Isaac Newton's law is usually called the law of inertia.0Forces are needed to overcome any fiction that may

be present. Forceces are also needed to set objectsin motion initially.

0Once an object is moving in a force-free environment, it will move in a  straight line indefinitely.

3.5 Mass - A messure of Inertia

0The more mass an object has, the greater its inertia and the more force it takes to change its state of motion.

0Mass is the quantity of matter in an object. Mass is a measure of the inertia of  and object. Mass is measured in the fundamental unit of kilograms.

0Weight is the force of gravity on an object. Weight depends on an object's location.  The mass of an object is the same weather the object is located on Earth, on the moon, or in outer space.

3.5 Mass - A messure of Inertia

0Mass and weight are proportional to each other in a given place. Objects with great mass have great weight, objects with little mass have little weight.

0 In most parts of the world, the measure of matter is commonly expressed in units of mass.  The SI unit of mass is the kilogram and it symbol is kg.

0The SI unit of force is the newton. The SI Symbol for the newton is N and is written with a capital letter because it is named after a person.

3.6 The Moving Earth Again

0The law of inertia states that objects in motion remain in motion if no unbalanced forces act on them.

0Copernicus announced the idea of a moving Earth in the sixteenth century. This controversial idea stimulated much argument and debate.

0Newton's work showed that objects on Earth move with Earth as Earth moves around the sun.  The law of inertia also shows the objects within moving vehicles move with the vehicles.

0Notions of motion today are very different from those of our distant ancestors.

Concept Summary

0Aristotle, the foremost Greek scientist, studied motion and divided it into two types: natural motion and violent motion.

0Copernicus reasoned that the simplest way to interpret astronomical observations was to assume that Earth and the other planets move around the sun.

0Galileo argured that only when friction is present - as it usually is - is a force needed to keep an object moving.

Concept Summary

0Newton'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 force.

0The more mass an object has, the greater its inertia and the more force it takes to change its state of motion.

0The law of inertia states that the objects in motion remain in motion if no unbalance forces act on them.