# Chapter 3 NEWTON’S 1 ST LAW INERTIA. HISTORY OF INERTIA Aristotle: force is necessary to maintain motion Galileo: objects maintain state of motion unless.

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Chapter 3 NEWTON’S 1 ST LAW INERTIA

HISTORY OF INERTIA Aristotle: force is necessary to maintain motion Galileo: objects maintain state of motion unless a force causes change Newton: Principia (principles of motion): An object at rest will stay at rest and an object in motion will stay in motion unless acted upon by an unbalanced force

WHAT IS “UNIFORM” MOTION? At a constant speed In a straight line NO acceleration There is no difference between standing still and moving at a constant velocity

MASS vs INERTIA Inertia is directly proportional to mass It is more difficult to change the motion of more massive objects than less massive objects It takes 3 miles of ocean to stop an aircraft carrier moving at 30 mph

MASS vs WEIGHT Mass: quantity of matter (kg) Mass: does NOT vary with location; NOT DEPENDENT ON GRAVITY Weight: force of gravity acting on mass; newtons (N) Weight: varies with location; depends on local gravity Inertia: proportional to mass

EQUILIBRIUM Condition when net force is zero Vector resultant is zero Acceleration is zero Maintains whatever motion already existed a = 0; v = k

WHY DO THINGS FALL STRAIGHT DOWN? Earth rotates (over 1000mph at equator) Everything on Earth rotates at same speed (including the atmosphere!) Falling objects appear to fall straight down

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