Mass
- One notion is that of a mass acting as an impediment to acceleration: from
Newton's famous second law (F = ma), when one applies a
force to a body it accelerates - for a given force, the smaller the mass,
the higher the acceleration. This is Inertial Mass.
- A related idea is the notion of mass as the source of a gravitational field
- Gravitational Mass. While again from Newton, while he was unaware
of the notion of a "field," he recognized the logical distinction
and did make specific reference to the possibility that gravitational and
inertial masses might be different, but now, as then, there is no evidence
for a difference.
- There is the somewhat fuzzy notion of mass as the amount of "stuff"
in a body, a measure of matter which is independent of weight.
- FInally, there is the identification of mass with energy, which of course
succinctly appears on tee shirts and is the result of the characteristically
simple questions that Albert Einstein asked and answered throughout his career.
This identification has its simple formulation as E = mc2.
We primarily trade in this fourth definition, which is related to the less
precise 3rd. When one cuts up masses into their smallest parts, we find that
the fundamental particles exhibit particular masses. In fact, mass values are
what distinguishes many of the fundamental particles from one another.
- For example the electron (a member of the category called leptons)
is exactly like its heavier cousin (constantly raining down on us from cosmic
rays) the muon. They both have negative charges, they both interact
with other particles in the same way - but the muon is precisely 206.76826
times heavier! Why this relationship and the other relative mass values of
all of the quarks and leptons?
- Light has partners also...massive ones (called the W and Z
bosons). Here we have clues and a description called the Standard Model suggests
that a Universe-wide, sudden change akin to condensation, gave these objecs
their mass.
- We're especially intrigued with the huge mass of the newest quark, the Top,
as it's more than a factor of 20 times heavier than the next massive Bottom
and 175 times heavier than a hydrogen atom.
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