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# Relativity/mass and energy

Question
QUESTION: in nuclear fusion mass is added from the new potential energy and it is lost again in fission. as this is not restricted to only nuclear binding forces is it possible that two magnets brought together would have a difference in mass?
Gene

ANSWER: Yes, because the total energy of the pair of magnets is reduced when they come together. If they are gently brought together by hand, the hands take away the energy. If they snap together, their temperature will rise a little, then cool, we may suppose. Anyway, lowered energy means lowered mass, although the effect is probably much too small to measure.

You have found an interesting example of relativity!

Ben

---------- FOLLOW-UP ----------

QUESTION: hello,thank you,
so if we only know of matter from its characteristics, then is it not conceivable that there actually is no matter; only mass with different observable characteristics that we call matter when it has certain characteristics?
thank you,
Gene

ANSWER: I wouldn't throw out the concept of matter. A proton has, not only mass, but also other properties, such as spin. charge, and magnetic moment. A neutron has about the same mass as a proton, but it is drastically different in other properties.

Ben

---------- FOLLOW-UP ----------

QUESTION: thank you, but are these properties that you listed as differentiating mass from matter not just all possibly as a result of the movement of the mass?
thank you,
gene

No, the properties are intrinsic to the particle and apart from mass have nothing to do with its motion.
The "rest mass" of the particle is an intrinsic part of its mass. The other properties are entirely independent of the motion of the particle.

The word "matter" is not a technical term, but I think you can attach it to a named particle, such as proton, neutron, photon, neutrino, meson, and other fundamental particles, each of which has properties that identify it in addition to its rest mass.

Ben

Relativity

Volunteer

#### Uncle Ben

##### Expertise

I can answer questions regarding Einstein's Theory of Relativity, particularly in Special Relativity. I will not answer homework questions or mathematical problems that require special symbols.

##### Experience

I have taught physics at the college level, undergraduate and graduate, for many years including Special Relativity. I have taught at Johns Hopkins, Case-Western, and MIT. I have also served as a staff member of the Commission on College Physics, which was supported by the National Science Foundation to recommend improvements in the curriculum of college physics departments in the US. I am also the author of a textbook titled Vector Calculus, which was used at MIT in the teaching of electromagnetic theory and relativity. My research interests were mainly in solid state physics, especially the properties of metals at low temperatures. I am listed in the publication known as American Men of Science.

Publications
I have dozens of papers published in the Physical Review and in the American Journal of Physics.

Education/Credentials
I hold a Ph.D. degree in physics from the Johns Hopkins University.

Past/Present Clients
Johns Hopkins University, Case-Western Reserve University, Massachusetts Institute of Technology, Empire State College, Georgetown University, Commission on College Physics, and UNESCO.