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Re: why do scalpels cut easily when moving?



The edge of the scalpel is a wedge. When you press straight down you have
the mechanical advantage of the full wedge angle. In effect you look
at the angle made by the surface in a plane perpendicular to the edge.
When drawn sideways the effective angle is the angle made by the surface
in a plane at a much reduced angle to the edge. This smaller angle gives
a much greater mechanical advantage. (The mechanical advantage is
proportional to the inverse of the tangent.)

On Wed, 21 Jan 1998, JOHN CAMERON wrote:

Dear Colleagues, I am a retired medical physicist from the U. of Wisconsin.
One of my retirement activities is to support and participate in a web page
called Electronic Medical Physics World (EMPW). The address is given at the
end. One of the services offered on this web page is "Ask your medical
physicist". Today I received the following question. I need your help.

"I am a surgical resident in the Netherlands. I have a question about my
scalpel. When the scalpel glides over the tissue, only a very slight
pressure is
needed to cut. When I do not move the scalpel, but just push it on the
tissue, a high pressure is needed. I can think of no explanation and
neither can my chief surgeon nor a physicist whom I contacted on Internet."
I don't know the answer but I suspect that some of the subscribers
to Phys-L will have some useful explanations. I promised to send the
questioner the results of your knowledge, ideas, hunches, etc. Thanks for
any help you can give me.
Those of you interested in radiation from medical x-rays may want
to read an article I recently submitted to Applied Radiology (a journal
read primarily by radiologists) titled: Explaining radiation to patients.
I would be happy to send it as an attachment to anyone who contacts me
directly by e-mail or by other means.
Best wishes, John Cameron

Check out ELECTRONIC MEDICAL PHYSICS WORLD - EMPW - which links to AAPM,
IOMP etc.at http://www.medphysics.wisc.edu/~empw and
the Bibliography of books and journals in Medical Physics and related
fields at http://www.medphysics.wisc.edu/~cameron.

John R. Cameron, we are at our winter home at 2678 SW 14th Dr.,
Gainesville, FL 32608 phones : 352/371-9865; Fax 352/371-9866 until about
May 15, 1998 We then revert back to our summer home:
2571 Porter Rd., P.O. Box 405, Lone Rock, WI 53556-0405 Phones:
608/583-2160; Fax: 608/583-2269

my e-mail all year is: jrcamero@facstaff.wisc.edu