COEFFICIENT OF STATIC AND DYNAMIC FRICTION IN WIDE RECEIVER GLOVES

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The coefficient of friction from four pair of Under Armour wide
receiver gloves was recorded after each pair had caught a certain
number of passes. The gloves were worn to catch passes from a Jugs
machine set at a speed of 50 mph (excluding the warm-up passes). The
Jugs machine was set up at a constant distance of 30 feet. Each subject
who caught passes started with a warm-up of 5 passes on the Jugs
machine set at 50 mph. Once the subjects put on the gloves, the only
thing they were allowed to do with their hands is catch the football. They
were instructed not to rub their hands together, touch anything or throw
the ball. All of this was to prevent any excess friction against the gloves.
To facilitate this, a trashcan was placed in front of the subject catching
the football where the football could easily be dropped.
The first pair of gloves were not worn to catch passes. They were
used as a baseline value for the coefficient of friction. Glove pairs 2-4
ranged in the number of passes each pair caught. Pair two caught 100
passes, pair three caught 200 passes and pair four caught 400 passes.
The coefficient of friction value was recorded using a force plate. Each
glove was placed palm side down on the force plate. Each glove was
attached to a string which was also attached to a motor (drill). A 1 kg
weight was then placed on top of the glove. The motor was turned on
and caused the glove to slide across the force plate at a constant
velocity. The coefficient of friction value for each glove was then
recorded. The coefficients of static (µs) and dynamic friction (µd) were
both calculated. The (µs) was calculated as static friction force (Fs)
divided by normal force (R) and the (µd) was calculated as dynamic
friction force (Fd) divided by R.
The results for the t-test and Cohen’s d effect size estimates are
displayed in Table 1. There was no statistical significance found in the t-
test or Cohen’s d effect size estimates for the coefficient of static friction
(µs). There was statistical significance found in both tests for the
dynamic friction (µd). The largest effect size was between 0-400
passes.
Table 1. Results for t-tests and Cohen’s d effect size estimates (p value
(d)) Static Dynamic
0-100 0.85(0.11) 0.01*(1.32+)
0-200 0.77(0.14) 0.26*(0.53^)
0-400 0.65(0.24) 0.00*(2.29+)
100-200 0.40(0.20) 0.01*(1.22+)
100-400 0.74(0.20) 0.00*(1.83+)
200-400 0.29(0.54) 0.21*(0.63^)
(*) = p≤0.05, (+) = large effect, (^) = moderate effect
The main purpose of this study was to test the coefficients of static
friction (µs) and dynamic friction (µd). There was no statistical difference
in any of the tests related to µs. There was statistically significant
difference in all of the tests related to µd. Furthermore, Cohen’s deffect
size estimates revealed moderate and high effect sizes for trials that
focused on µd.It is appropriate that there was only statistical and
practical differences with tests related to µdand not µssince passes are
moving before being caught.
Although there was no statistical difference in relation to the µs,
there was variations in the statistical difference of the µd. While the
findings were high in some areas, it was unexpectedly lower in others.
The changes in coefficient of dynamic friction between 0-100 and 0-400
were consistent and logical, but the gloves used to catch 200 passes
produced a somewhat surprising result as the value did not decrease at
the same rate. This may be an issue with the gloves themselves or
there could also be a breaking in period for the gloves which could have
affected the results. While, this study cannot say when the gloves are
less effective than not wearing gloves at all, the current study noted a
decrease in the performance of gloves with increases in numbers of
catches. This supports the notion that gloves should be replaced at
some point and further research should be done to indicate this
threshold.
Gloves are a main piece of equipment for many positions in the
game of football. The most thought of purpose in gloves is for receivers.
Receivers wear gloves to improve their catching skills. Many receivers
in the NFL admit gloves make a difference (Perioff, 2010). This makes
sense because an adhesion type substance can increase the coefficient
of friction. Chalk, for example increases the friction coefficient for rock
climbers and their hand holds (Amca et al., 2012). Throughout the
history of football, there has been other adhesion substances used. One
such substance is Stickum. Stickum was a blob-like substance that
helped receivers defensive backs catch the football (Florio, 2015). This
substance was in use in the 1970s and banned in the early 1980s. In
the NFL today receivers use gloves that are as effective as Stickum
ever was (Florio, 2015). It is not uncommon to see receivers use several
pair of gloves throughout a season. Even though it would be ideal for all
levels of football to have the financial means to buy several pair of
gloves for the receivers throughout the year, this is not the case for
those in lower budget situations. It is helpful to know under what
circumstances a pair of gloves lose their effect and when anew pair
would be beneficial.
While gloves are worn by receivers to improve their catching skills,
it can be difficult to measure when they lose effectiveness. There are
ways to quantify this difference and measure the coefficient of friction of
the gloves at different stages of their use. Therefore the purpose of this
investigation was to evaluate the coefficient of static and dynamic
friction at several stages of their use based upon number of passes
caught.
COEFFICIENT OF STATIC AND DYNAMIC FRICTION IN WIDE RECEIVER
GLOVES
REFERENCES
DISCUSSION AND CONCLUSION
INTRODUCTION
Norman, T.L., Nilson, K.W., and Bailey, C.A.
Sport Performance Enhancement Education and Development (SPEED) Center, Department of Exercise Science,
LaGrange College, LaGrange, GA
www.lagrange.edu/strength
www.facebook.com/LCSPEEDCenter
METHODS
RESULTS
ACKNOWLEDGEMENTS
Amca, A. M., Vigouroux, L., Aritan, S., & Berton, E. (2012). The effect of
chalk on the finger–hold friction coefficient in rock climbing. Sports
Biomechanics,11(4), 473-479.
Florio, M. (2015 November 5). NFL notes launch of Stickum ban. Retrieved
from:http://profootballtalk.nbcsports.com/2015/11/05/nfl-notes-launch-of-
stickum-ban/
Perloff, A. (2010). Sticky Fingers. Sports Illustrated,113(18), 30.
Thomas, J. R. (2015). Research Methods in Physical Activity.
Champaign, Illinois: Human
Kinetics
The authors of this investigation would like to thank Coach Chris
Prewett and Johns Creek High School Football for providing the Jugs
machine and facility for the data collection to take place.