1. Types of Forces

2. Four Main Forces in Universe Gravity F g. Electromagnetic EM Strong Nuclear Strong or Nuclear Weak Nuclear Weak All Forces fall into one of the above categories.

3. Common Forces Weight F g = mg gravity interaction with mass. Weight depends on gravity, Mass does not. What is mass? Amount of matter in object.

4. Normal Force (reaction force) – perpendicular to the surfaces in contact. Opposite to weight on horizontal surface. F n = -W

5. What if you’re leaning on a wall. Where is the normal force?

6. Where is it now?

7. Sliding Friction – force acts at contact between surfaces. Direction of friction opposes velocity or attempted velocity. F f =  F n  is constant Which way is friction?

8. Which way is the book moving? Right Left The box is not moving.

9. Tension – transmitted through string, rope, or wire by forces at each end.

10. Air Resistance – air friction. Big reason for bad fuel economy in cars.

11. Spring or Elastic Force – Force applied by stretched or compressed spring described by Hooke’s Law.

12. Magnetic Force

13. Electrical

14. Force is a vector quantity. It has direction. Acceleration –  v – is always in the same direction as the net force!!

15. Free Body Diagrams Diagrams to show relative magnitude & direction of all vector forces acting on a body. Sizes of arrows show magnitude of force. Arrowhead shows direction of forces.

16. What can you say for sure about the object in the free body diagram below? 1. It is at rest. 2. It is in motion to the left. 3. It is in motion to the right 4. Not enough information to know.

17. Balanced & Unbalanced Forces

18. An unbalanced force is a resultant or net force. What is the F net ? What can you say about the motion? 12 N 4 N F net = - 8 N or 8 N left The object shows Acceleration left.

19. A bird flies with a constant velocity to the left at a constant altitude. What is the free body diagram?

20. F bird up F grav F bird left F air fric V = 0 up so no F net up. F bird cancels Fgrav. Const v horiz. So no F net left. Friction balanced by force of bird left.

21. Assignment Handout “Free Body Diagrams”

22. Number One

23. Number Two

24. Number Three

25. Number Four