Tweet
Dear Colleagues,
I posted a message to ask for help to solve a soccer ball pressure
problem. A student in the master program of biomedical engineering did
a study on the impact forces in soccer heading. She used soccer balls
in three sixes with three inflation pressures. She had an
unproportional increase in ball mass when the inflation pressure
increased from 12 PSI to 14 PSI. She had the same results after
repeating the tests. She could not give her thesis committee a
convincing explanation. To try to help her, I posted a message to ask
for help.
With the help from many colleageus, especially Cameron Barr in
Biokinetics & Associates, Ltd., we finally found the problem. The
original measurement of ball masses at 10 PSI and 12 PSI was in error.
The air pump and the scale were in different locations. The student had
to test ball masses on three different days. She calibrated the scale
only before the first test (14 PSI). Another group of students used the
scale with different calibration after that. That caused error in the
measurement of ball masses at 12 and 10 PSI. There was a coincident
pattern in the lab schedule when she repeated the test. That gave her
the same results in retest. After her thesis committee requested her to
re-test again, she thought the error was in ball mass at 14 PSI because
the increase in ball mass from 10 PSI to 12 PSI was reasonable. No need
to say that she still could not find the problem after repeatedly
testing the ball mass at 14 PSI several times. Then I recieved a
message from Cameron who pointed out the ball mass should be around 400
g when the inflation pressure is between 10 PSI and 14 PSI. This made
the student realize the error was in ball masses at 10 PSI and 12 PSI.
After repeating the test three times again, she finally had the
reasonable results:
0PSI 10PSI 12PSI 14PSI
Size3 0.3197 0.3221 0.3225 0.3230
Size4 0.3566 0.3597 0.3603 0.3611
Size5 0.4204 0.4236 0.4243 0.4251
I sincerely thank everybody who replied my message and offered help, and
apologize for any confusion caused by this problem.
--
Bing Yu, Ph.D.
Assistant Professor
Director
Center for Human Movement Science
Division of Physical Therapy
The University of North Carolina at Chapel Hill
Chapel Hill, NC 27599-7135
Tel: 919-843-8643
Fax: 919-966-3678
E-mail: byu@med.unc.edu
---------------------------------------------------------------
To unsubscribe send SIGNOFF BIOMCH-L to LISTSERV@nic.surfnet.nl
For information and archives: http://isb.ri.ccf.org/biomch-l
---------------------------------------------------------------
I posted a message to ask for help to solve a soccer ball pressure
problem. A student in the master program of biomedical engineering did
a study on the impact forces in soccer heading. She used soccer balls
in three sixes with three inflation pressures. She had an
unproportional increase in ball mass when the inflation pressure
increased from 12 PSI to 14 PSI. She had the same results after
repeating the tests. She could not give her thesis committee a
convincing explanation. To try to help her, I posted a message to ask
for help.
With the help from many colleageus, especially Cameron Barr in
Biokinetics & Associates, Ltd., we finally found the problem. The
original measurement of ball masses at 10 PSI and 12 PSI was in error.
The air pump and the scale were in different locations. The student had
to test ball masses on three different days. She calibrated the scale
only before the first test (14 PSI). Another group of students used the
scale with different calibration after that. That caused error in the
measurement of ball masses at 12 and 10 PSI. There was a coincident
pattern in the lab schedule when she repeated the test. That gave her
the same results in retest. After her thesis committee requested her to
re-test again, she thought the error was in ball mass at 14 PSI because
the increase in ball mass from 10 PSI to 12 PSI was reasonable. No need
to say that she still could not find the problem after repeatedly
testing the ball mass at 14 PSI several times. Then I recieved a
message from Cameron who pointed out the ball mass should be around 400
g when the inflation pressure is between 10 PSI and 14 PSI. This made
the student realize the error was in ball masses at 10 PSI and 12 PSI.
After repeating the test three times again, she finally had the
reasonable results:
0PSI 10PSI 12PSI 14PSI
Size3 0.3197 0.3221 0.3225 0.3230
Size4 0.3566 0.3597 0.3603 0.3611
Size5 0.4204 0.4236 0.4243 0.4251
I sincerely thank everybody who replied my message and offered help, and
apologize for any confusion caused by this problem.
--
Bing Yu, Ph.D.
Assistant Professor
Director
Center for Human Movement Science
Division of Physical Therapy
The University of North Carolina at Chapel Hill
Chapel Hill, NC 27599-7135
Tel: 919-843-8643
Fax: 919-966-3678
E-mail: byu@med.unc.edu
---------------------------------------------------------------
To unsubscribe send SIGNOFF BIOMCH-L to LISTSERV@nic.surfnet.nl
For information and archives: http://isb.ri.ccf.org/biomch-l
---------------------------------------------------------------