Does Your Shoe Mu?
Modified from activity located at http://www.woodstown.org/ACS/resources/ap/ch1/act6.pdf
When you walk into a shoe store there are hundred of different kids of shoes. How do you
determine what to buy? Women might buy for how pretty a shoe is, or if it will match a particular
outfit. Women have to determine the height of the heel and are concerned with many other factors.
Athletes have to determine which shoe is right for them based on the sport they play. Basketball
shoes differ from bowling shoes, which differ from track shoes.
Why do you think that some sports require special footwear?
We are going to look at one of the factors that might affect which shoe you choose to purchase.
We are going to look at the surface gripping ability of the shoe.
Before we begin our testing write down some factors that you think would affect the surface
gripping ability of the shoe.
Procedure:
1. Take a shoe that one of the group members is wearing and determine its weight using either
a spring scale marked in Newtons, or use a platform balance and convert mass in kg to
weight in N. Record this value along with a description of the shoe.
2. Place the shoe on a horizontal surface as designated by your teacher. Attach a spring scale
or force probe to the shoe. You may have to be a little inventive as to how to do this. Keep
in mind you must hold the spring scale or force probe parallel to the surface and the shoe
must remain flat on the surface. It might be necessary to add some weight to the shoe to
keep the entire sole in contact with the horizontal surface. Try to distribute the extra
weight evenly. If you add weight, be sure you note that as part of the weight of the shoe
that you recorded in step 1.
3. Keeping the spring scale or force probe parallel to the surface, slowing and carefully apply
force to the scale or probe. Be careful not to jerk or pull too hard. Have another lab
partner watch the spring scale or computer screen while applying the force so that “the
puller” can concentrate on watching the shoe and gradually increasing the force. Once the
shoe starts to move try to keep the force constant by watching the scale or computer screen.
It might take some practice to get this just right.
What happened to the magnitude of the force just after the shoe began to move?
4. Measure and record the amount of force needed to START the shoe moving and then the
amount of force needed to KEEP the shoe moving at a slow constant speed.
5. Use the data you have collected to calculate the static and kinetic coefficients of friction.
Calculations: Be sure to include a labeled force diagram for each calculation.
To calculate the coefficient of Static Friction (s):
s = Force required to Start the object into motion
the perpendicular force the surface exerts on the object
Note: The perpendicular
force is the normal force labeled FN.
To calculate the coefficient of Kinetic Friction (k):
s = Force required to Keep the object in motion
the perpendicular force the surface exerts on the object
Note: The perpendicular
force is the normal force labeled FN.
6. Repeat Steps 2-5 for the same shoe and surface, but approximately double the weight of the
shoe and any additional weight you used. Be sure the additional weight is evenly
distributed. Calculate the s and k for these conditions.
7. Repeat steps 2-5 and also step 6, but use a different horizontal surface. Calculate the s and
k for the various conditions.
EXTENSION: You might try testing the mu of your shoe when the surface is wet and see how
water affects the gripping ability.
Additional Questions:
Within experimental error, does the weight of the shoe affect either the static or kinetic
coefficients of friction when measured between the same two surfaces? Justify your answer.
Based on your experimental evidence, do you think the weight of the athlete wearing a
particular shoe would affect the coefficient of friction? Why or why not?
If a basketball player’s shoes supply the “right amount of friction” for the home court, can
the athlete count on the “right amount of friction” on all courts? Why or why not?
What other qualities of a shoe might an athlete want to consider when purchasing a shoe?
Name at least two sports where the athlete would want to minimize friction.
What do you think the soles of the shoes that are worn by dancers on Dancing With The
Stars are made out of? Do you think the friction needs to be minimized or maximized?
Support your answer.