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Measuring Contact Pressure
Name: Jeannie
Status: Student
Grade: 9-12
Location: CA
Country: United States
Date: Spring 2010
Question:
My project is designed to determine which fabrics
retain the most residue from deodorants after soaking in water
and then drying. I would like to know if there is a way to
measure the amount of pressure being applied; How would I be
able to apply the same amount of pressure each time I glide the
deodorant onto the fabrics?
Replies:
Hi Jeannie,
Sounds like you are looking for a few mechanical design suggestions. I
assume you are wanting to compare "stick type" deodorants (not "roll on"
types). In that case, I suggest mounting the deodorant under test on the end
of a wooden stick about 2 feet long, together with a known weight. The stick
would be parallel to the table that has the fabric laying on it, and the
"business end" of the deodorant would be contacting the fabric with the
weight supplying the required constant pressure. You would then hold the
opposite end of the stick and push or pull to move the deodorant (at the
other end) across the fabric.
Regards,
Bob Wilson
Hi Jeannie,
That sounds like an interesting experiment.
I would use some clamps and light wood or metal strips to build a 'trailer
type' apparatus that would allow you to drag the deodorant container across
the different fabric patches. This would assure you were not adding any
additional load onto the container as you applied the deodorant.
Then you would have to use a small scale (like a postage meter) to determine
the weight of the deodorant container and the portion of the trailer
apparatus weight that transferred through the container. If that was not
sufficient weight to apply the amount of deodorant you wanted you would add
a small weight as necessary.
Once a proper weight was established you would then have to determine the
area at the end of the deodorant stick that was contacting the fabric. This
would be difficult since I think the edges are rounded and the area might
change a little after each use. Anyway, the idea would be to divide the
load by the contact area to determine the actual contact press use (pounds /
in2).
Of course if you did not actually care about the precise contact pressure you
could use a new deodorant stick for each application to assure the ends of
the stick were equal in size.
Well, after all that I will now probably think of your experiment each time I
use some deodorant.
Carlton Schroeder
Eagle River, WI
Probably your best bet would be to place a known weight atop the the deodorant
container and be careful not to apply any up-or-down force to the dispenser as
you push it across the fabric. That way you will know that the pressure is the
same in all cases. Weight differences as the deodorants become depleted (as
they get lighter) will not be significant if the added weight is at least a
few times larger than the weights of the deodorant samples. (If you want to
be very careful about this, you can scale the weight to the cross-sectional
area of each sample.)
Richard BArrans, Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
One easy way is to make a weighed jig that presses the deodorant on a
horizontal surface, and then simply pull the deodorant horizontally
along the surface being treated.
As for how to measure a pressure, there are tons of pressure
transducers out there that can measure the force -- or you can use a
simple weight scale (tared to zero with the deodorant removed).
Hope this helps,
Burr Zimmerman
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Update: June 2012
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