3. Friction Every day you see moving objects come to a stop. The force that brings nearly everything to a stop is friction FRICTION is the force that acts to resist movement between two touching surfaces.

4. Objects cannot move with a constant speed unless a net force is applied because friction is always acting to slow down the motion If friction could be removed, an object in motion would continue to move in a straight line with constant speed. Friction, continued

5. In the vacuum of outer space, there is no friction to slow motion Therefore objects continue to move indefinitely (like the moon around the earth) Friction, continued

6. If two objects are in contact, frictional forces always try to prevent one object from sliding on the other object. If you rub your hand against a tabletop, you can feel the friction push against the motion of your hand. Friction will always slow an object down. Opposing Sliding

7. STATIC FRICTION prevents an object from moving when a force is applied Static Friction It is caused by the attraction between atoms on the 2 touching surfaces which cause the surfaces to stick together

8. Generally, the rougher the surface or the heavier the object, the more static friction. To move the object, you have to exert a force large enough to break the bonds holding two surfaces together. Static Friction, continued

9. SLIDING FRICTION slows down an object that slides. You have to keep pushing to overcome the force of sliding friction. Sliding Friction

10. A force must be applied to move the rough areas of one surface past the rough areas of the other. Sliding Friction, continued Sliding friction is due to the microscopic roughness of two surfaces. What are some examples of sliding friction you encounter in your everyday life?

11. ROLLING FRICTION, occurs between the ground and the part of the tire touching the ground. Rolling Friction Rolling friction keeps the tire from slipping on the ground and exerts force on the tires that pushes the object forward.

12. It’s usually easier to pull a load on a wagon or cart that has wheels rather than drag the load along the ground. Rolling Friction, continued Rolling friction between the wheels and the ground is LESS than the sliding friction between the load and the ground. Why does a cart have wheels?

13. Fluid Friction FLUID FRICTION occurs between an object and air or water. Examples: skydivers jump out of a plane boat traveling through water

14. ANSWER THE FOLLOWING SELF CHECK QUESTIONS:

15. Question List and give an example of the four types of friction:

16. Question List and give an example of the four types of friction: Answer Rolling Friction (roller skates) Sliding Friction (plate sliding across a table) Static Friction (pushing a desk) Fluid Friction (a person swimming through the water)