1. Friction

2. Friction F f The symbol for friction is ________ The unit for friction is _____________ ①

3. What is friction? Friction is the __________ that ____________ the __________between objects. ②

4. Your teacher (or a volunteer) is going to push a book across the table. Predict what is going to happen to the motion of the book when the person stops pushing it. Predict ③ Will it keep moving at the same speed in the same direction forever? Will it slow down and come to a stop? Will it speed up and crash through the wall?

5. Observe What did you observe happen to the book? ④

6. Explain Why do you think the book moved the way it did after the person stopped pushing it? ⑤

7. Friction

8. If the book is pulled at a slow, __________________, the forces on the book are _________________. ⑥ The Net Force is _________.

9. Arrows are often used to show forces. The diagram below shows a book being pulled to the right at a slow, constant speed. Draw and label a second arrow to show the force of friction that acts on the book (make sure it points in the correct direction and is the correct size).. Friction points in the _____________ direction as the pulling force. The friction force is _________ size as the pulling force.

10. ⑧ If the book is pulled at a slow constant speed, the ________________ should be the __________ as the ____________________. The teacher (or a volunteer) will pull the book at a slow, constant speed across the table with a spring scale. The force that is read off the spring scale is the same size as the force of friction. Force of friction on the book = F f = _________ N

11. Does FRICTION depend on the TYPE OF SURFACE? With a partner, take a spring scale and an object and try pulling the object at a slow, constant speed across several surfaces. ⑨

12. Does FRICTION depend on WEIGHT? With your partner, take a spring sale and a set of masses  First weigh the mass by hanging it from a spring scale.  Next pull the mass along the table at a slow and constant speed.  Record the force required to overcome the force of friction. ⑩

13. The force of friction when objects are not yet sliding past one another is called ___________ FRICTION. Your teacher is going to try to push an object, but it won’t move. ⑪

14. The force of friction when objects are sliding past one another is called ______________FRICTION. Your teacher is going to push the same object again, but this time it moves. ⑫

15. Friction can __________________________________ ⑬