1. Chapter 3 NEWTON’S 1 ST LAW INERTIA

2. 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

3. 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

4. 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

5. 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

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

7. 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