Chapter 4 - Laws of Motion Notes 4.1a – Newton’s 1st Law

Objectives Define Newton’s First Law of Motion. Explain how inertia and mass are related. Define Newton’s Second Law of Motion.

Isaac Newton British Scientist 1642-1727 British Scientist Published 3 rules in 1687 to explain how forces and motion are related Rules apply to motion of all everyday objects as well as planets, stars and galaxies That’s why we call it Universal Gravitation

Newton’s first law of motion States that the motion of an object changes only if an unbalanced force acts on the object If forces are balanced, object doesn’t change its motion Only unbalanced forces change velocity

Inertia Tendency of an object to resist a change in its motion 1st Law = LAW OF INERTIA

Inertia & mass Inertia varies with mass Mass is a quantity which depends solely on inertia More inertia = more mass A more massive object has a greater tendency to resist changes in its state of motion

Inertia & your car Inertia explains what happens in a car crash Car and your body are moving at the same speed Brakes slow and stop car Seat belts slow and stop your body Seat belts loosen slightly to decrease the force acting on your body and increase the time it takes to slow your body (GOOD THING)

Newton’s 2nd Law Describes how the forces exerted on an object, are related to its mass, and its acceleration.

Newton’s second law of motion States that the acceleration of an object is in the same direction as the net force on the object, and that the acceleration can be calculated from the following equation:

Calculating Net Force Newton’s second law also can be used to calculate the net force if mass and acceleration are known

In-Class Assignment/Homework Article reading Answer the questions on your lecture tutuorail and return article to front table Pg. 103 #1-7