1. Newton’s First Law

2. INERTIA An object at rest remains at rest, and an object in motion continues with constant velocity unless it experiences a net external force

3. Stationary objects don’t want to move

4. Moving objects don’t want to stop

5. When you are in a car that is accelerating, you feel as if you are being pushed back. Your body (actually the inertia of your body) is resisting the increase in speed. When the car comes to a sudden stop, your body wants to continue in a forward motion.

6. When stopping, the coffee tends to spill forward When accelerating, the coffee tends to spill on you.

7. Sudden Stops - seat belts help your body resist the tendency to keep moving. (rapid deceleration) Sudden Starts - head rests stop the head from being pushed back. (rapid positive acceleration)

8. What will happen without seatbelt?

9. Misconception!! - If no force acts on a moving object, it will eventually come to rest. - Motion requires the presence on a force. Truth!! - Only a force can cause a change in the motion of a moving object. - An object moves at a constant velocity or not at all if there is no force acting on it. What happens when you stop applying a force to an object?

10. External Force A single force that acts on an object as a result of the interactions between objects and its environment

11. Net External Force The vector sum of all forces acting on a body. Can be found using the methods for finding resultant vectors

12. Objects motion is the same as if the net external force was the only force acting on the object

13. Do forces always cause an object to move? We need to talk about NET FORCES! NO!! F 1 = 30 N F 2 = 10 N F net = 20 N Equilibrium occurs when the net force equals zero.

14. Object can be in equilibrium even when many forces act on it When equal force but opposite direction, no change in motion If one team applies greater force, acceleration will occur in the direction of that force

15. Equilibrium Objects that are either at rest or are moving with constant velocity are said to be in equilibrium When Σ F X = 0 and Σ F Y = 0 then the vector sum of ALL forces acting on the body is equal to zero and the body is in equilibrium