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Re: why do scalpels cut easily when moving?



On Wed, 21 Jan 1998, JOHN CAMERON wrote:

"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

It COULD be as simple as this: static friction is much higher than dynamic
friction. When the scalpel is pushed into tissue, the sides of the cut
adhere to the blade and prevent forward motion. When the scalpel is swept
across tissue, adhesion takes place only in tiny spots and therefor is
greatly reduced.

OR, when the scalpel is swept across tissue, perhaps the motion and the
pressure at the very edge of the blade cause extremely high temperatures
to appear, and this affects the chemical bonds of the tissue. This might
resemble "electric discharge machining", where the high spots of the
workpiece attract arcs and are vaporised. The high spots in the tissue
would experience high friction and be cooked if not vaporised.

Or maybe both of the above. Possibly neither, if someone else suggests
other possible mechanisms.

Don't "wiggling knife" scalpels exist, where the blade is vibrated with
ultrasound? If you can figure out the keywords which hit papers about
these, perhaps you can find contemporary research about how knives work.


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