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Which year? The sidereal year? The tropical year? The anomalistic year? The calendar year (and whose calendar)? The sidereal year is the average amount of time it takes the Earth to make one complete orbit about the Sun with respect to the fixed stars. The tropical year is the amount of average amount of time between successive spring equinoxes. The ...


13

If I saw the word "amp" written as such in a paper in my field (astrophysics) it would strike me as a bit informal. I would expect to see the full "ampere" written. That said, it is rare to actually write out the full name of a unit; usually it follows a number and is given its standard abbreviation. When abbreviated to e.g. "$5\ \mathrm{A}$", I would ...


11

Technically, apparently, your teacher is correct. BIPM and NIST In the official brochure from the Bureau international des poids et mesures (BIPM, the keepers of SI units) in §5.1 Unit symbols we find: It is not permissible to use abbreviations for unit symbols or unit names, such as sec (for either s or second), sq. mm (for either mm2 or ...


3

why does it seem improper to add many speeds (or velocities)? Adding speeds is ofttimes inappropriate even in Newtonian mechanics. Suppose Mark is moving 3 m/s eastward with respect to Bob, and John is moving 3 m/s westward with respect to Mark. The relative velocity between Bob and John is zero rather than the 6 m/s suggested by adding speeds. You can ...


3

Your question, as of right now, seems confused to me. An extensive property of a system is one that scales with the system size. An intensive property is independent of the system size. For example, consider a system $A_1$ with $N$ particles in a volume $V$, with density $\rho=\frac{N}{V}$. Now, we consider two of these systems separately, $A_1$ and $A_2$, ...


3

I think that your description that the points of the configuration manifold are possible states of the system is as close to a precise definition as one will find. So for $n$ particles in three dimensions, the configuration manifold is just $(\mathbb{R}^3)^n$. As for how this relates to constraints, consider the simplest example: two particles attached with ...


2

I can respond to your first quote about finely grained. Roughly speaking, a finely grained substance is a collection of a large number of "small" objects. Think of sand. Large or course grained substances, on the other hand, are compased of many "large" objects. Here's a picture of course- and fine-grained salt. Note that one would indeed have a larger ...


1

A year is defined by the time earth takes to circle the sun once: http://en.wikipedia.org/wiki/Year This does however not correspond to an even number of days. The SI unit of time is the second and $1\,\mathrm{day} = 24\cdot 3600\,\mathrm s$


1

When "year" is used as a unit for things unrelated to Earth's orbit, such as distances in light years or the age of the universe in years, it is the Julian year of exactly 365.25·86400 SI seconds.


1

According to the Wikipedia page, amp is acceptable, but is not a correct SI unit. I think your instructor is being thorough and making certain that you know the correct term to use.


1

OP is essentially asking about terminology. As usual, be prepared that different authors call different notions differently. Well, here is a suggestion: Call the configuration space before (after) the constraints are implemented for the extended (physical) configuration space, respectively. More generally, if an author is talking about a configuration ...


1

Work is done by something or someone, expending energy by exerting a force on an object. I'm not quite sure what the context is of your quote, but I'd imagine that it could be a scenario much like the following one: Imagine a ball with some mass $m$ being lifted by a man. The gravitational force from Earth is pulling the ball down, but the person ...


1

Note that the notion of work $W=\int_{\gamma} {\bf F}\cdot \mathrm{d}{\bf r}$ depends on the force ${\bf F}$. Here ${\bf F}$ could e.g. be a gravitational force or a frictional force, etc., leading to a gravitational work or a frictional work, respectively. The phrase work done against a force is shorthand for work $W_1$ done by a force ${\bf ...


1

Taking answers and comments into account, my own current conclusion is that velocity is an intensive property, provided the system considered is homogeneous, at least with respect to speed. Like other intensive properties, this may depend on scale, and cease to have meaning at molecular level. I did not intend to write an answer to my own question but ... ...


1

Actually, no. The original Dirac's concept was the annihilation in the literal meaning of that word. According to that concept, anti-particle was a particle which has anti-energy, that is, negative energy. But, after discovery of positron, and when collision of it and electron was performed, and showed that the result are two gamma-photons (when slow ...


1

Duration is certainly a more physical concept than time. Duration is something you may measure between timelike separated events while time is always something you compute by adding up duration measurements + an arbitrary constant to fix the origin. Duration is experimental and relational while time (e.g. GPS time) is an abstract a posteriori ...


1

Okay, I am going to try and give this a shot, but this is most probably not going to be a decisive answer. Let us operate with the term event time and duration and consider only special relativity (SR). The conclusions of general relativity should be the same for reasonable space-times. (e.g. without closed time-like curves etc.) We expect event time to ...


1

For me in my own field (optics, where one most often comes across it in engineering considerations), "amps" is common spoken usage, particularly for compound words such as milliamp or microamp. For written usage, I'm afraid I like to see the full name - it is, after all, recalling a very great man of science André-Marie Ampère. Even so, curiously, the SI ...



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