1. Newtons 1st Law Chapter 4: Pages 130-135 Holt Physics

2. “Law of Inertia” Sir Isaac Newton 1687- An object at rest tends to stay at rest, and an object in motion tends to stay in motion unless acted on by an outside force. Inertia – the tendency of an object to maintain its current state of motion.

3. Newton’s 1st Law If the car were to abruptly stop and the seat belts were not being worn, then the passengers in motion would continue in motion. The passengers would likely be propelled from the car and be hurled into the air becomes projectiles and continue in projectile-like motion.

4. Newton’s 1st Law In this example, the ladder continues in motion because no outside force changes its original motion, until the ladder hits the ground.

5. Determining Net external force External force – a force acting on an object resulting from interaction between object and environment Examples: friction, gravity, every single push or pull

6. Net External Force Net external force – total force (sum of all forces) acting on an object  Referred to as the Resultant force An object may have many forces acting on it, but still be in equilibrium

7. Equilibrium Equilibrium – the state of a body in which there is no change in its motion  Either at rest or in motion  Net external force on an object = 0 Newtons

8. Inertia Inertia is proportional to mass Mass is a measurement of inertia More mass = More inertia

9. Equations Σ  (Greek letter sigma) means “sum of all” ΣFx = sum of all forces in x-direction ΣFy = sum of all forces in y-direction

10. Equations Fx = F total (cosθ)  x-component of force Fy = F total (sinθ)  y-component of force

11. Equations F total 2 = F x 2 + F y 2  Resultant force (F-total) (net external force)

12. Homework 1. Read Chapter 4-3 2. Page 133 #1-3 3. Page 135 #1-3