1. Newton’s 2nd Law of Motion

2. Forces A ______or _______ The cause of an ____________ Cause of a change in an object’s state of motion Cause objects to ___________ or ______________ Cause a change of _____________ Unit of force: _______________

3. Free Body Diagrams One object ______ Forces represented as arrows placed where they _________ Length of the arrows should represent the _____________of the force F g down, F N perpendicular to surface, F f parallel to surface opposing motion

4. Free Body Diagrams Used to analyze the forces affecting the motion of a single object Shows only the forces acting on an object

5. Finding F net We define forces pointing up or right as _______________ We define forces pointing left or down as _____________ To get F net : Add all parallel forces and subtract off antiparallel forces

6. Example A mover pushes a box with a 20 Newton force to the right. His friend sees him struggling so he helps push the box by applying a 25 Newton force in the same direction. What is the net force on the box?

7. Example Now a 3 rd mover, not being too bright, decides to help by pushing with a 14 Newton force in the opposite direction. What is the net force now?

8. Newton’s 2nd Law The acceleration of an object is directly proportional to the net external force acting on the object and inversely proportional to the mass of the object or: ____________

11. Types of Forces Contact forces: _____________- (F t or T) - The force that a “string” pulls on an object _______________- (F N or N) - Force that a surface applies to an object (the direction is  to the surface) __________- (F f ) - To be defined later

12. F, applied force  A physical push or a pull

13. F N, Normal Force (N) A force that a surface applies to an object “Normal” means ______________ The direction of the normal force is perpendicular to the ____________ surface

14. Tension - (F t or T)  Tension (force) in a string or rope  Strings only ________

15. Types of Forces Field Forces (Action at Distance) Force of _________(F g ) or Weight F g =_______, - WEIGHT IS THE FORCE OF GRAVITY ___________ Where g = _____________ Electricity/Magnetism

16. Force of Friction F f Always parallel to the surface Acts opposite to the direction of motion F f = μ F N Where μ is the coefficient of friction It is determined between the two surfaces in contact (it will vary depending upon the surface)

17. Common μ’s Materials μ Oak on oak, dry0.30 Steel on steel, dry0.41 greasy0.12 Steel on ice0.01 Rubber on asphalt, Dry1.07 wet0.95 Rubber on ice0.005