1. How could you have gotten to school today in a world with no friction?

2. Albert tries to push a couch across a carpeted floor and it does not move. Is this an example of friction?

3. This is an example of static friction.
Static friction is a force that exists between an object and the surface upon which it rests that resists motion. Static friction can increase up to a maximum point, equal to the normal force times the coefficient of static friction.
Fstatic friction≤ µsFN. If the applied force is greater than this value, the object will begin to move and static friction will no longer exist.

4. What’s the Normal Force?
The normal force is the force that is perpendicular to the surface upon which an object rests; for example, the force the table exerts upon a book that sits atop it.
Question to think about: Is the normal force always equal and opposite to the weight of the object? Think about our elevator lab…

5. Coefficient of static friction:
Property of the 2 surfaces that contact each other; Some examples….
Steel on Steel
0.74
Wood on Wood
Rubber on concrete
1.0 for dry and 0.4 for wet
Ice on Ice
0.1
Synovial Joints in Humans
0.01
Do demo with spring scale—pull a mass and take the reading and then add more mass and take a reading.

6. You push a couch across a carpeted floor and it begins to move
You push a couch across a carpeted floor and it begins to move. Is there friction in this example ?

7. There’s no static friction since the couch is moving….
But there is kinetic friction, which acts in the direction opposite an object’s motion.
Fkinetic friction = µkFN where FN is the normal force and µk is the coefficient of kinetic friction.

8. Examples of µk Steel on Steel 0.57 Wood on Wood 0.2 Rubber on Concrete
0.8 for dry and 0.1 for wet
Ice on Ice
0.03
Synovial joints in humans
0.003

9. What are some examples of the importance of friction in real-world applications?
Hint: Assuming Beaker fell down, what shoes should he have been wearing to keep him from falling? Assuming he can’t get up, what should be different about his lab coat?