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Re: Inertia





On Fri, 28 Nov 1997, brian whatcott wrote:

In reading Definition III of Principia, I get a sense that Newton
could have originated this particular term - he reaches it by means
of a small discussion:

"The Vis Insita, or innate force of matter, is a power of resisting,
by which every body, as much as in it lies, continues in its present
state, whether it be of rest, or of moving uniformly forwards in a
right line.
...
A body, from the inert nature of matter, is not without difficulty
put out of its state of rest or motion. Upon which account, this
vis insita may, by a most significant name, be called inertia
('vis inertiae') or force of inactivity."

Newton, trans Motte/Cajori


Thanks, Brian, for saving me the trouble of dusting off my copy of the
Principia.

It should be noted that in the older literature, the word translated as
"Force" isn't necessarily force in the modern sense. It often meant
"property of" or "capacity for" or "tendency to". So we shouldn't confuse
Newton's "Force of inertia" with the F (or -F) in F=ma.

Another example is "electromotive force" (EMF) which survives in modern
books, and obviously isn't a force in the modern sense. It's original
meaning was something like "That agent (force) which causes charge
(electro-) to move (motive)."

-- Donald

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Dr. Donald E. Simanek Office: 717-893-2079
Prof. of Physics Internet: dsimanek@eagle.lhup.edu
Lock Haven University, Lock Haven, PA. 17745 CIS: 73147,2166
Home page: http://www.lhup.edu/~dsimanek FAX: 717-893-2047
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