Name______

Date______

Period_____

Problem: Friction is a force that acts in the opposite direction to motion. How does the amount of friction between a shoe and a surface compare for different brands of shoe?

Materials: Three or more different brands of shoes, 2 spring scales (5 N and 20 N), mass sets, tape, large paper clips, triple beam balance

Explanation: Shoes are designed to deal with various frictional forces, including these:

a.  Starting friction, which is involved when you start from a stopped position

b.  Forward-stopping friction, which is involved when you come to a forward stop

c.  Sideways-stopping friction, which is involved when you come to a sideways stop

Procedure:

1.  Place each shoe you are testing on the triple beam balance. Then put masses in each shoe so that the total mass of the shoe plus the masses inside is 1000 g (1 kg). Spread the masses out evenly inside the shoe.

2.  Tape a paper clip to each shoe and then attach a spring scale to the paper clip. To test

  1. starting friction, attach the paper clip to the back of the shoe
  2. forward-stopping friction, attach the paper clip to the front of the shoe
  3. sideways-stopping friction, attach the paper clip to the side of the shoe

3.  To measure starting friction, pull the shoe backward until it starts to move. Use the 20 N scale first. If the reading is less than 5 N, use a 5 N scale. The force necessary to make the shoe start moving is equal to the friction force. Record the starting friction force in your data table.

4.  To measure either type of stopping friction, use the spring scale to pull each shoe at a slow, constant speed. Record the reading as the stopping friction in your data table.

Data:

Shoe Brand / Starting Friction (N) / Sideways-Stopping Friction (N) / Forward-Stopping Friction (N)
1.
2.
3.
4.

Analysis:

1.  Controlling variables: What are the independent and dependent variables?

Independent:

Dependent:

2.  Observing: Why is the reading on the spring scale equal to the friction force in each case?

3.  Interpreting Data: Which shoe had the most starting friction? Which had the most forward-stopping friction? Which has the most sideways-stopping friction?

4.  Drawing Conclusions: Do you think that using a shoe with a small amount of mass in it is a fair test of the friction of the shoes? Why or why not? (Hint: consider that shoes are used with people’s feet inside them.)

5.  Inferring: Why did you pull the shoe at a slow speed to test for stopping friction? Why did you pull a shoe that wasn’t moving to test starting friction?

6.  Developing Hypothesis: Can you identify a relationship between the brand of shoe and the amount of friction you observed? If so, describe the relationship. What do you observe that might cause one shoe to grip the floor better than another?

7.  Extension: How could this be done differently? Write down one idea that you come up with that would change one of the variables in this experiment. Remember to only change one variable!