MadSci Network: Physics

Re: What does the p in momentum stand for and what does it mean?

Date: Mon Dec 13 11:26:08 1999
Posted By: Judith E. Bush, Staff, Educational Technology Programs, Franklin Institute Science Museum
Area of science: Physics
ID: 944538807.Ph

After  years of using the relationship p = m/v, i don't think
i ever asked myself "why p?" 

It's a good question.

First i turned to the dictionary. 

Impetus (Date: 1641)
   from Latin in- + petere to go to, seek -- from Greek
   petesthai to fly, piptein to fall, pteron wing

Impulse (Date: 1611)
   from Latin impulsus, from impellere to impel

Momentum (Date: 1610)
   from New Latin, movement

Pulse (Date: 14th century)
  from Latin pulsus, literally, beating, from pellere to drive, push,

Well, there seems to be a deep common linguistic root here, from the
beating pulse of a heart to the beating of a bird's wing. In fact our
"push" (Date: 13th century) and "pull" (Date: before 12th century)
derive from the Latin pellere.

Still, why p? Well, Newton thought of "moments" in a more
mathematical, abstract sense in the calculus he was inventing (moments
of inertia, for example). In the scientific community at the time
Newton published the Principia, *impetus* was the quality of an object
that was moving independent of an observed force. Furthermore, the
equation p=m/v wasn't given first by Newton, but was developed
afterwards. Many scientist/mathematicians developed what we now call
"Newtonian Mechanics," and it's easy to imagine some sticking with the
old impetus while others used the new momentum. P was a convenient
symbol -- m would be confused with mass, i is too often used to
indicate an instance of an object. (Mi usually means the mass of the
ith object.)

To read about the concepts of impetus and momentum, you can read these
two essays.
.com/book/chapter2.htm http://www.cor

And if this answer isn't satisfying, you can track down Volkmar
Schüller at the Max Planck Institute for the History of Science. (No
email address, He 
has translated
Newton's Principia and is preparing a glossary of Newton's technical
and scientific terminology.


judith bush

Judith E. Bush                                
The Franklin Institute Science Museum           New Media Specialist
222 N. 20th Street                                  1 (215) 448-1236
Philadelphia, PA 19103-1194 USA                    AOL IM judielaine

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