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## Main Question or Discussion Point

Mass on earth can be understood as weight in Kg, or units of E/C^2, but what is a viable definition that does not use the words "substance" or "matter" or some other circular term?

- Thread starter Buckeye
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Mass on earth can be understood as weight in Kg, or units of E/C^2, but what is a viable definition that does not use the words "substance" or "matter" or some other circular term?

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I am not sure I completely understand your question. We usually refer to gravitational mass as the one subject to gravitation (giving weight on Earth), and to inertial mass as the one a body "opposes to modifications of its movement". General relativity in particular postulates that those two are equal. Nobody has ever observed that gravitational mass is any different from inertial mass : all bodies "fall at the same rate". Gravitation can thus be described in geometrical terms.Mass on earth can be understood as weight in Kg, or units of E/C^2, but what is a viable definition that does not use the words "substance" or "matter" or some other circular term?

Now, E=m is the total energy of a body in its own rest frame, which is just his mass according to this equation. This is valid anywhere (with or without a gravitational field, that is

Do you want yet another "equivalent" definition of mass, that is a "third" manifestation of mass, on top of inertial and gravitational ?

- #3

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No. I do not need another equation. I need a definition in words, not equations of equalities, that explain what mass is. For example: Mass is equal to the attractive-repulsive interactions of one or more atomic particles.I am not sure I completely understand your question. We usually refer to gravitational mass as the one subject to gravitation (giving weight on Earth), and to inertial mass as the one a body "opposes to modifications of its movement". General relativity in particular postulates that those two are equal. Nobody has ever observed that gravitational mass is any different from inertial mass : all bodies "fall at the same rate". Gravitation can thus be described in geometrical terms.

Now, E=m is the total energy of a body in its own rest frame, which is just his mass according to this equation. This is valid anywhere (with or without a gravitational field, that isalsoin "empty vacuum" far away from any measurable source). In an arbitrary referential, the energy has a momentum "component" corresponding to kinetic energy/quantity of movement : [tex]E^{2}=\vec{p}\,^{2}+m^{2}[/tex] (in units such that c=1).

Do you want yet another "equivalent" definition of mass, that is a "third" manifestation of mass, on top of inertial and gravitational ?

Or, perhaps: Mass is due to the harmonic interaction of one set of atomic particles to another set of atomic particles.

Does that help?

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Then this discussion will end belonging to GD, not HENPPNo. I do not need another equation.

This is not a joke : words are useful scientifically to communicate only if they can be backed up by an equation. Mathematics is the only un-ambiguous way to communicate between us human beings.

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malawi_glenn

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Well atleast when it comes to physics, the language of physics is math after all.Mathematics is the only un-ambiguous way to communicate between us human beings.

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Does that mean that physicists are simply mathematicians pretending to be scientists?Well atleast when it comes to physics, the language of physics is math after all.

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Vanadium 50

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Remember, one can take any definition of anything whatsoever and follow up with "But what is it

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Please pay attention to what you post. Your logic is completely wrong. Mathematicians create the language of mathematics. Physicists use the language of mathematics to communicate between them. The equations come of course together with text in order to make the communication easier. But essentially, if you can not put your claims into equations, those are completely useless.Does that mean that physicists are simply mathematicians pretending to be scientists?

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malawi_glenn

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yeah, what if we have encountered something fundamental and elementary?

Remember, one can take any definition of anything whatsoever and follow up with "But what is it?" This path doesn't really go anywhere.really

What if I asked the string theorists: "But what is a string made up of? What is it really?" We can go on forever..

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malawi_glenn

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What is your definition of science? Science is a quite broad term, http://en.wikipedia.org/wiki/ScienceDoes that mean that physicists are simply mathematicians pretending to be scientists?

Physical science differs quite much from chemistry, and organic chemistry in perticular. Physical science differs from philosophy, and from archeology and so on.

Physics is an interplay between making theories, models, experiment and interprenting data. The theories are always constraint under some axioms, for instance the requirement of beeing invariant to Lorentz boosts, Gauge invariance etc. No axioms can be prooven, but they can be motivated. This sort of interplay is strongly related to philosophy, that you always must put up axioms that can't be proven in order to formulate a world view. In the old days, physics was called "Natural philosophy" and the foundators of the math we use today (calculus etc) was largely developed by people who where philosophers and experimental scientists.

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George Jones

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No. Who was it?

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malawi_glenn

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And it was R Feynman.

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George Jones

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Feynman was at Cal Tech, not Berkeley.And it was R Feynman.

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Evo

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Locked, this is pointless.

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