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Re: [Phys-L] Definition of Mass



Introductory physics students need an operational definition, and the one currently used by the metrologists seems best. A balance is used to compare an object to the standard body, which by definition is the only thing in the universe that has a mass of exactly one kilogram.

Understanding that fields are responsible for the mass of the matter that we're made of is something that introductory students can also be made aware of without complicating or contradicting the above definition.

And this gives us the opportunity to point out that the mass of most of the universe is a deep mystery to physicists (dark matter and dark energy).

And the fact that the standard body will soon be obsolete as a definition of mass is something that can also make an interesting discussion for introductory students. It gives them an opportunity to understand the basics of the science of metrology.



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From: Phys-l on behalf of coachpayne@aol.com
Sent: Wed 23-Oct-13 12:15 PM
To: phys-l@phys-l.org
Subject: [Phys-L] Definition of Mass



Interesting statement from the paper by Gregg Swackhamerin the Modeling Resource paper CognitiveResources for Understanding Energy (Draft March 31, 2005): "since over 90%of the mass of Mt. Rainier or bread, arises not from particles but from energystored in the strong fields holding the constituent quarks together, it is apretty accurate statement in many instances to say that energy is there justlike bread in a breadbox." (Wilczek, Frank, "Mass without Mass I: Most ofMatter," Physics Today, November, 1999, pp. 11-13) This might be commonknowledge to most or all of the folks on this list, but it was novel to me. I'denjoy reading your comments on this. Howdo others of you define the term mass? Iunderstand the inertial and gravitational meanings, but how do you discuss massin your classes?

Thanks.

Charlie Payne
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