The mu of your shoe- measuring friction

Background:
Friction is a force that opposes motion.Objects stop moving because of friction.Friction is simply two surfaces acting on each other.
Friction depends on the type of surface an object is on, and the amount of surface area that the friction is acting on.
Can you name some frictions that would oppose motion?

Materials:
Spring scale
Shoe
Different surfaces

Directions:

1. Zero your spring scale This is done by moving the metal tab at the top of the scale up or down until the reading is zero.( Repeat this before each measurement).
2. Make a data table with 4 columns:1.surface: 2. force to pull the shoe across surface: 3.weight of the shoe (the shoe hanging free from the spring scale): and 4.mu.
3. Measure the weight of your shoe by hanging it from the spring scale.Record this in your data table. This will be the same for all trials.
4. Place the shoe on the table. Attach the spring scale to the shoe by using the shoe's laces or to the loop on the back of the shoe.Pull the shoe across the table while keeping the sole of the shoe flat on the table.
5. For surface, write tabletop. Measure and record the force it takes to keep the shoe moving ( not the force it takes to get the shoe moving) across the table.
6. Measure the force it takes to move your shoe across different surfaces. Record the surface and the force in your data table. Always try to pull the shoe at the same speed.
7. Use your data to calculate mu which is the coefficient of friction by using this equation:
8. mu= force to pull shoe/ weight of the shoe. example: if it takes 1.5N to pull the shoe across the table and the shoe weighs 5N, then 1.5/5= 0.3. 0.3 is the coefficient of friction for the table.

Questions:
Where did you find that the friction was the highest?
As friction increased what happened to the amount of force it took to move the shoe?
What kind of shoe would have the most friction? The least? Why?

Conclusion:
How is friction measured?