1. 2*7 Frictional Force: The Mu of the Shoe
WDYS? (p210) .
WDYT?
Some sports require special shoes because _____.
Different features of a shoe are useful for different sports because _____.

2. 2*7 Mini-Lab
Set up:
You will pull 2 different shoes across the table and read the “force” on a scale.
(gym & something else)
Question: Which one will be harder to pull?
Prediction:
Observation:

3. 2*7 Mini-Lab (p210) DATA: TABLE-TOP Mass Weight Force to get it going
Force to keep it going
Shoe 1
AVERAGE

4. 2*7 Mini-Lab (p210) Analysis:
When you were pulling on the shoe (either) name the 4 forces acting on the shoe.
What was the force needed to get the gym shoe moving? To keep it moving?
What was the force needed to get the other shoe moving? To keep it moving?
What would happen to these measurements if we added weight?

5. 2*7 Mini-Lab (p210) 4. What is the “mu” of the shoe on this surface?
The coefficient of sliding friction is represented by
(μ) = force of friction = ←
perpendicular force exerted ↑
by the surface on the object
4. What is the “mu” of the shoe on this surface?

6. 2*7 Mini-Lab (p210)
5. Now, lets do it again on the carpet  Question: Will the “mu” be higher or lower than the table top? PREDICTION: ___________________________

7. 2*7 Mini-Lab(p210) 5. Using the CARPET data: 
Sketch a FBD of the shoe with 4 forces:
Calculate μ =
Will the value of μ will be DIFFERENT with the surface? _________________.
Why do you think so?
Conclusion:
The rougher the surface, the (higher/Lower) the “mu” is.

8. 2*7 Notes (p )
Analyzing the Forces Acting on the Shoe
When an object moves at constant velocity the net forces equal ZERO
Constant Velocity = NO Acceleration = Balanced Forces = Net Force is ZERO = Arrows have SAME LENGTH!!!

9. 2*7 Notes (p )
HORIZONTALLY
The shoe moved forward at a slow constant velocity, so there is equal and opposite force = FRICTION
VERTICALLY
The shoe did NOT move up nor down, therefore the net forces must be BALANCED and EQUAL ZERO
Normal Force  acts perpendicular to the surface; it’s the force of the 2nd object

10. 2*7 Notes (p212-214) (μ) = force of friction = ← normal force ↑
2. Coefficient of Sliding Friction, μ
(μ) = force of friction = ←
normal force ↑
(μ) does NOT have units
(μ) expressed in decimals
A change in the SURFACE causes a change in (μ)
the rougher the surface, the greater the (μ)
The smoother the surface, the less the (μ)

11. 2*7 Notes
STATIC friction: The amount of friction between 2 surfaces when they are not moving relative to each other (needed to hold an object in place) DYNAMIC Friction : the amount of friction between 2 surfaces when they are moving relative to each other Dynamic Friction < Static Friction

12. 2*7 Notes (p )
EXAMPLE:
What is the coefficient of friction between a 200N object being pushed with a force of 100 N at constant velocity?

13. 2*7 TOTD (25pts) Draw AND Label the 4 forces on an object.
If an object has constant velocity, then the acceleration is _____.
If the forces are balanced, then the arrows are _____.
What is the equal but opposite force to the “pull”?
What is the NAME of the equal but opposite force to gravity?