1. Chapter 13 Forces

2. What is Force? A push or pull You are exerting a force right now (against the chair, or against the atmosphere) Other objects are also exerting a force on you!

3. What are the Four Forces? Electromagnetic Strong Weak Gravity

4. A force: Gives energy to an object Causes objects to: 1.start moving 2.stop moving 3.change direction 4.change shape

5. Two forces: Can be exerted in the same direction (add together) Can be exerted in opposite directions (subtract them)

6. Net Force:

7. Balanced vs. Unbalanced: Balanced = forces in opposite directions that are equal Unbalanced = total force is in the same direction - changes the motion of an object

8. Balanced

9. Unbalanced

10. Friction: A force that opposes motion Will cause an object to slow down & finally stop When two surfaces touch each other, there will always be some friction because the surface face is not completely smooth

11. Friction: The amount of friction between two surfaces depends on how hard the surfaces are pushed together & the type of material of the two objects A heavy object will force the two surfaces together more than a lighter object

12. Friction: To move an object, the force you exert on an object in one direction must be greater than the force of friction on that object in the opposite direction

13. Types of Friction: 1.Sliding – solid objects slide over one another 2.Rolling – an object uses wheels or ball bearing to roll over another object 3.Fluid – object moves across or through a fluid (all gases & liquids)

14. What type of friction?

17. Putting it all together: