Purpose:
The purpose of this investigation is first to determine the coefficient of static friction for shoes; and second to compare the difference in friction of shoes on wet and dry surfaces.

Every individual in the class needs to submit one of their shoes for this lab. Before the static coefficient of friction is calculated for the shoes, the class will predict which three shoes will have the greatest and which three shoes will have the least coefficient of static friction. This lab will be competed in groups of three. The requirements for the lab write-up are listed below.

Materials: To complete this investigation each group will need the following materials:

3 different shoes protractor/ruler masking tape whiteboard/board of any kind of board

water mister towels dry erase marker electric balance

Procedure:

Predictions – Each individual needs to pick one of their shoes to be used in the lab (either left or right.) BEFORE you do any experimenting predict which of your group’s shoes will have the highest dry µs,max and highest wet µs,max. Record these predictions in your data table. Also, predict which shoe will have the lowest dry µs,max and highest wet µs,max.

Experimentation
1. Record in the data table each of the shoes that your group will use in this investigation. Include the brand of shoe and what kind of shoe it is (all purpose, flip-flop, high heel, basketball, tennis, moonboot etc.)

2. The whiteboards need to have a starting location clearly marked with tape so that every time the shoes start at the same spot. Place the toe of the shoe on the line while the board is horizontal. It is important that the entire shoe be on the board – you can place the shoes laterally on the board if need be.

3. One member of the group will SLOWLY raise the board and watch the shoe while the other two members will note the height of the board when the shoe starts to move and measure with protractors this angle. When the shoe JUST BEGINS TO SLIP record the angle of incline. Make sure that the two people screening the angles agree on the angle at which motion began. If there is disagreement, take another measurement and raise the board more slowly.


4. Repeat step 3 for each shoe at least 3 times. Average the results of the trials. Record your averaged information on the class data sheet.


5. Repeat the procedure (steps 1-4) but this time SLIGHTLY wet the board with the water mister. Record this data on the class sheet.

6. Using the average angle for each shoe, complete the calculations to determine the static coefficient of friction (wet and dry). Once the group has determined the shoe with the highest and lowest coefficients of static friction for each shoe, write the data for those shoes on the board to see if the class’s predictions were correct.

Sample Data Table: Make two tables like this one on your own paper.

Student/Shoe Information / Average angles for each trial
Student / Brand / Type of shoe (purpose) / Trial
1 / Trial
2 / Trial
3 / Average of trials 1à3 / Coefficient of Static Friction (µ)
This is an example data sheet. Create your own for you group using these headings and this format. Each group is to submit its completed data table.
You will have one table for the dry trials and a separate table for the wet trials.

Lab Write Up:

Each group must submit one lab write up that includes the following items:
Pre-Lab predictions 3 points
Data Tables and observations 5 points
Lab Calculations – you only need to show a (full) calculation for ONE trial. 2 points

Answers to all of the questions 20 points

Questions: On your OWN paper answer these questions thoroughly, legibly and in complete sentences.

1. (3 points) Which of the shoes in your group had the greatest coefficient of (dry) static friction? Why do you think this is? What is the intended purpose of this shoe?
Was your group correct in its prediction? Discuss.

2. (3 points) Which of the shoes in your group had the smallest coefficient of friction? Why do you think this is? What is the intended purpose of this shoe?
Was your group correct in its prediction? Discuss.

3. (3 points) Did the same shoe(s) have the lowest coefficients of friction when tested on the wet surface? Why do you think they were the same or different?
Specifically, how do you think the water changed the coefficient of friction?

4. (3 points) What factors affect the coefficient of static friction? Explain how, specifically, they affect it.

5. (2 point) Why do you think the individual trials of the shoes were performed 3 times per shoe?
6. (2 points) What are some of the sources of error in this lab?

7. (4 points) For what purpose(s) would shoes with a high coefficient of static friction be designed? For what purpose(s) would shoes with a low coefficient of static friction be designed? Give an example for each and be specific as to why a high/low coefficient is desirable.

See your instructors for an optional related friction and shoes lab.


Optional Surface Area and Shoe Friction Lab 20 points

This assignment/lab is to be entirely completed outside of class in groups of 3 or less. The grade for the each member of the group is the same. Pick your group members wisely. This is an optional assignment that will count toward your score regardless of your final score. That being said, make sure you complete the lab thoroughly and well. Read all of the instructions and include all of the requirements for the write-up.

Purpose

So far when discussing friction we have not discussed if the size of the object has an effect on surface area. To take the Static Friction Shoe Lab further, your group’s challenge is to go and test if surface area influences the amount of static friction on an object. What better location for a physics lab on friction than a shoe store! Thousands of shoes just begging to be tested!

Procedure

This lab is to only test if the surface area influences the amount of friction. To insure that the material of the shoe is exactly the same you are to test the SAME style shoe in at least 3 different sizes. In addition your group needs make sure that your results are not unique to one style of shoe, so you must test at least 3 different shoe types or brands. You may stick with one type of shoe (athletic, comfort, dress, stupid furry boots, etc) or you can keep it all the same. It is up to your group to decide. Work to ensure the most exact data possible. Think about what will give you the best possible data.

Requirements

Since you will be doing this entire lab outside of class, your group will have to verify that all of you participated in the data collection or analysis. Prior to going to a store to complete the lab, your group should construct the data table which will be used to gather data. You are to include a picture of the store name where you went to do the lab. Once at the store, your group must get a signature of either the manager or someone at the customer service desk on the page containing your data table. This will signify that you have permission to conduct the experiment at the store. Failure to receive the signature will result in a zero for this lab. Also each group is to take pictures of each set of shoes (of 3 different sizes) such as 3 Nikes, 3 Addidas and 3 (ugh) Uggs.

After you have gathered all of the data, create a single graph with each type of shoe that will BEST show whether or not surface area influences static friction. Be sure to label the graph with all of the appropriate details. All of your observations, data, and conclusions including answers to the post lab questions should be typed up in a paragraph or two. Make sure that your conclusions align with the data and consult the table below to see how points will be distributed.

Post Lab Questions

1. Based on your results do you think that the coefficient of friction varies with the (surface) area of contact between two surfaces?

2. How could you determine (experimentally & numerically) if the surface area of an object affects the friction between it and a given surface? Write a detailed explanation on how you would test this in a lab.

Points

Signature 0 points No signature is -20 points.

Data Table 4 points

Pictures of Shoes 3 points Need at least 9 shoes total. (less than 9 shoes = -20 points)

Graph 5 points

Conclusions 8 points