1. All About Forces http://www.youtube.com/watc h?v=HK8afQRrOck

2. Forces General Characteristics:  They are vectors  Push or Pull  Units = Newtons, Pounds Newton = force required to accelerate 1 kg at a rate of 1 m/s²

3. Nature of Forces Forces exist in pairs (its impossible for a single force to act on an object) Forces arise as a result of actions / reactions between objects There are always forces acting on all objects ***There are 4 fundamental forces**  Gravitational, electromagnetic, strong nuclear, weak nuclear

4. Classification Of Forces Contact & Long-Range & Short Range Contact:  Frictional Force  Applied Force  Normal Force  Tension Force Long Range:  Gravitational  Electromagnetic Short Range:  Strong Nuclear  Weak Nuclear

5. Gravitational Force Weakest of all forces Only noticed when one object is massive Acts over infinite distances

6. Electromagnetic Force Can be repulsive or attractive Acts between objects with an electrical charge Holds atoms and molecules together

7. Strong Nuclear Force Strongest of all forces Only acts over distances comparable to the size of an atom The force that holds protons and neutrons together

8. Weak Nuclear Force Also acts over small distances Involved in radioactive decay We will study gravitational & electromagnetic forces later on…

9. Drawing Free Body Diagrams A book is at rest on a tabletop.

10. Drawing Free Body Diagrams A girl is suspended motionless from the ceiling by two ropes.

11. Drawing Free Body Diagrams An egg is free-falling from a nest in a tree. Neglect air resistance.

12. Drawing Free Body Diagrams A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance.

13. Drawing Free Body Diagrams A car is coasting to the right and slowing down.

14. Drawing Free Body Diagrams A force is applied to the right to drag a sled across loosely packed snow with a rightward acceleration.

15. Newton’s 3 Laws of Motion #1 = Objects at rest stay at rest, objects in motion stay in motion (unless acted on by an outside force). Inertia  Tendency of an object to resist change  http://www.youtube.com/watch?v=-- MDILG7Znk

17. Net Force and Equilibrium The net force is the vector sum of all the forces that act upon an object  When forces are Unbalanced Equilibrium  If the net force on an object is Zero  Object is either at rest or a constant velocity

19. Determine the missing forces