SDS - Traction Test Activity

Traction Test Activity

Introduction

Note: This activity was do-developed with Mark Blaser and was funded, in part, by an NSTA and Toyota TAPESTRY grant.

Think of the people who wipe sweat off the court after players collide and fall down. If they were to ignore their job and the sweat was left on the floor, the next time your favorite player drove for the basket you'd see something more akin to a hockey game, with players sliding all over the place, as all traction would be lost. Putting a thin amount of water on a wood floor compromises its frictional properties and causes shoes to slip and slide, at best causing a missed shot and a laugh, but, at worst, a career ending injury. Friction and its close cousin traction, are central to sport. From throwing a curve ball to stopping and popping--the best athletes are, in a sense, masters of friction.

When a shoe strikes the ground, a frictional force develops between the ground and the shoe. This frictional force, somewhat explained by Newton's Third Law, must be considered when designing sport shoes. Sport researchers and shoe designers deal with frictional forces by studying traction. They design shoes to optimize the amount of traction provided. This is no simple task because optimal traction varies considerably not only between sports, but also between movements in particular sports.

Figure 1 - Traction Takes a Player Places

Think about what happens when this player lands. How many ways will friction and traction play a part in his game?

Try to list all the different factors you would have to consider in designing a shoe that provides optimal traction for other sports. Would your design vary for different positions in each sport? Would it vary if the sport were played on a different surface?

bball player at work

A marathon runner needs shoes that help her efficiently maintain forward motion. For the most part, traction considerations for running shoes focus on providing enough friction to allow the runner to push off on each stride. A basketball player, however, requires shoes that provide enough traction to run in a straight line, like the runner, but must also provide more traction under certain instances, like during quick cuts to the basket that may require several changes in direction.

To balance all this the sport researcher interested in friction and how it effects traction must keep in mind that the amount of friction is dependent on what part of the shoe is in contact with the ground, what material the shoe is made of, the pattern or spikes on the outsole of the shoe, as well as what the ground, or substrate, is made of. The focus for sport researchers is the outside of the shoe--by using different materials, textures, ridges, or spikes, researchers can take advantage of friction, or, as in ice hockey, lack of friction, to improve the performance of an athlete.

To help facilitate the development of outsoles for various sport shoe designs, sport researchers have designed traction tests that allow them to test different materials and patterns of outsoles as well as different substrate types. In its simplest form, a sport researcher uses a traction test to see how much force is required to move a shoe a specific distance in a set time. The more force it takes to move a shoe, the greater the friction between the outsole and the ground, and the greater the traction.

Traction Test

Figure 2 - Slam Dunk Science Traction Test Set-up.

The sample shoe must be pulled 15cm in 3 seconds. The computer and force probe tell the student how much force is required to move the shoe.

By comparing values between shoes the researcher can tell which shoe has the best traction. In general, the greater the amount of force required, the greater the traction.

Can a shoe have too much traction?

(Note: For more information on the traction, outsole characteristics, and the use of traction tests in a sport research lab, refer to the Shoe Design Section and Lab Tools sections of the Slam Dunk Science Activity Guide.)

Objectives

In this activity students will set up and collect data from a traction test. At the end of this activity students will understand:

How and why a sport researcher or shoe designer would use traction testing,
How to measure the traction (frictional) properties for a material being considered for use in an outsole, or currently being used in a shoe,
How the surface, or substrate, impacts the ability of a shoe to provide traction,
How to design further traction tests on their own.

This activity, provides an overview of setting up and running traction tests similar to those used in a sport research lab. The format, like all Slam Dunk Science Activities, is designed to leave further avenues of research

Materials

Macintosh or PC-compatible Computer
Universal Laboratory Interface (ULI)
Logger Pro Software (Older versions of Vernier Software also can be used)
Force Probe (Vernier Student Probe works fine)
Variety of shoes or materials for testing

Procedure

This procedure uses Logger Pro, a force probe, and a ULI available through Vernier Software. This setup, running on a computer, provides a good balance between ease of use, features, and cost. Other hardware and software can be substituted. In fact, a "low tech" version of the traction test can be run without computers using spring scales and careful observation.

It is suggested that you familiarize yourself with the Logger Pro software, force probe, and ULI before you start this procedure. This activity is based on the assumption that you have done so before you start.

It is important to realize that the traction test as outlined here is relatively simple. You will most likely see how you can modify the test to improve its accuracy. The traction test allows you to perform reasonably accurate tests with reproducible results. As you go through this activity you will, no doubt, think of ways to improve on the traction test design. Please feel free to share your ideas so that they can be made available for other students using Slam Dunk Science in the classroom.

Before you get started, think about the many factors that might influence traction in a shoe. For this activity, focus just on a shoe designed for basketball. Use the table below to list factors, how they might effect traction, and how a shoe designer might design a shoe for optimal traction relative to each factor.

Factor Traction Need Design Considerations

Running in basketball allow player to run forward without slipping outsole must have adequate traction where the shoe hits the ground (heel)

Setting up the Traction Test Device (See Figure 2 as a guide for setting up the traction test)

Find a clear path on a surface you want to test shoes or potential outsole materials on. The path must be long enough to let you pull the shoe smoothly and consistently for a set period of time. You can vary the type of surface depending on the sport you are interested in studying. For example, you may use a wood or cement surface depending on if you are testing traction on indoor or outdoor basketball courts.
Label a starting point and mark off a 15cm path down which you will pull the shoe.
Prepare the shoe or object to test by securing a string or wire through the bottom two lace holes. This loop will be used to attach the force probe to the shoe.
Place the heel of the shoe at the beginning of the test path.
Place a 1000g mass in the area of the shoe that you want to test. You might place it in the heel to test rearfoot traction, or the front of the shoe to test forefoot traction.
Place the force probe in the loop and practice pulling the shoe smoothly and consistently 15cm in 3 seconds. Practice until you feel you can repeat the movement smoothly and consistently.

Setting up the Force Probe, ULI, and Logger Pro Software

Connect the ULI to the computer and connect the Force Probe to Port 1. Turn on the ULI.
Open Logger Pro and under the "Setup Menu" select "Sensor" to bring up the Sensor Properties screen. Click on the Sensor Setup tab and select "Force-ULI Force Probe" from the sensor options.
Calibrate the probe by clicking on the Calibrate tab and then the "Perform Now" button. Follow the steps below to calibrate the probe:

With no mass on the probe, hold it steady. Once the value for input 1 has stabilized click on "Keep".
Hang a mass of 500g on the probe and enter a value of "4.90" into the Value 2 field. Once the value for input 2 has stabilized click on "Keep". You are ready to collect data.

Collecting Data

In a sport research lab, the basic technique for testing traction is to place a mass on a shoe to be tested and measure the amount of force required to move the shoe a specific distance in a specific time. For our test you use a 1000g mass placed in the heel area of the shoe. The traction test will let you measure how much force (in Newtons) is required to move the shoe 15cm in 3 seconds.

The first factor listed in the table above dealt with running in basketball. The traction need listed indicated a design for an outsole that had adequate traction where the shoe hits the ground so that the player could run forward without slipping. In this simple test you will measure how traction varies in the rearfoot region in three different conditions--a basic low priced basketball shoe, a more expensive basketball shoe, and a sock. This test will help you begin to answer the question: "What is adequate traction?"

After you have calibrated the traction test device, collect data as follows:

Enter the name of the shoe or object to be tested, in Data Table 1 - Traction Test Results. Attach loop of wire to the front of shoe or object.
Place the shoe or object on the test surface, a wood table can be used to simulate a basketball floor, and place heel of shoe or object at the beginning of 15cm test path.
Place 1000g weight in heel to simulate mass of player standing in shoe.
Connect the force probe to the loop and get ready to collect data. Have a partner click on "Collect" button in Logger Pro. When computer begins collecting data, pull shoe smoothly and consistently over the 15 cm test path. Remember to complete the 15cm distance in 3 seconds.
At the end of the data collection have your partner click on "Stop". (Note: As you familiarize yourself with the Logger Pro software and its many functions you may want to customize your data collection by using trigger events and setting a specific sampling rate and sampling time.)
To determine the amount of force required to move the object 15cm in 3 seconds you must calculate the area under the curve defined by the data you collected. Fortunately Logger Pro makes this very easy by automatically calculating the integral of the force/time curve. To get the integral:

Use the mouse to point to where you began to apply force to move the shoe-- this is at the beginning of your graph. Click and hold the mouse button down.
Use the mouse to drag the pointer to the place on the curve, 3 seconds later, where your test ended. Release the mouse button. You have highlighted the area of the curve you want to integrate.
Under the "Analyze" command on the menu select "Integral." This will give you the area under the curve you highlighted, which will tell you the total force required to pull the object tested 15cm in 3 seconds. Record this number in Data Table 1

You may want to print out your data and graph before testing a new shoe or object by using Logger Pro's print function.
Repeat for each condition.

Condition Load Distance Total Force (Integral)

Discussion

Let's see what a sport researcher might do with data collected with the traction test. First of all, it is important to realize that to improve the quality of your data you must pay attention to things like testing only one variable at a time and controlling other variables that might influence the outcome of your experiment. You should also do repeated trials for each condition and, minimally average the values to improve the quality of your conclusions. Data from one test on three different conditions are entered in the data table below.

Condition Load Distance Total Force (Integral)

Old model b-ball shoe 1000g 15cm 12.87N

New model b-ball shoe 1000g 15cm 23.60N

Sock 1000g 15cm 5.8N

Use this data, or data you collected, to answer the following questions:

Which condition provided the best traction?
Which condition provided the least amount of traction?
Is there any specific aspect of each shoe that you think might explain the results? (Hint: Is it the material, or the pattern?)
Can you use the traction test to design another experiment to test your explanation in question 3?
What type of injuries might be caused by using a shoe, like the old model basketball shoe, that might not provide enough traction for running during a game?
How would you change this test to make it more accurate? (Hint: Is 1000g enough to simulate the mass of an athlete standing in the shoe?)

The data above is very simple. Try to design an experiment and modify the impact test procedure to answer the following questions:

How are different moves like spinning or cutting influenced by traction?
How does the traction characteristics of a shoe change over the course of a season?
How do different surfaces influence traction?
What makes for the optimal traction in various sports other than basketball?
Friction is not only the basic force at work in traction, it is also the reason that outsoles of shoes wear out. Why don't shoe companies make an outsole that lasts forever?