# Activity for HDE 226868‭

Type On... Excerpt Status Date
Edit Post #285644 Post edited:
9 months ago
Edit Post #285644 Post edited:
9 months ago
Edit Post #285644 Initial revision 9 months ago
Question How are the assumptions behind two ways of deriving the Rayleigh-Jeans law related?
The Rayleigh-Jeans law does a good job of describing the spectral radiance of a black body at low frequencies: $$B{\nu}(T)=\frac{2kT\nu^2}{c^2}$$ with $T$ the temperature and $\nu$ the frequency. There are a couple of ways to derive it. One, requiring no explicit assumptions about the energy range ...
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9 months ago
Edit Post #284410 Initial revision about 1 year ago
Question Is it possible to derive the Dieterici equation starting from assumptions about microstates?
I was introduced to a somewhat novel derivation of the ideal gas law that starts by thinking about the number of microstates of an ideal gas, $\Omega$. Say we have a gas with a single particle in a volume $V$. Doubling the volume should double the number of microstates, as it doubles the possible pos...
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about 1 year ago
Edit Post #284016 Initial revision about 1 year ago
Answer A: What is semiholonomic?
Semi-holonomic constraints look something like the following: $$f(\mathbf{q},t)=\sum{i=1}^nfi(\mathbf{q},t)\dot{q}i+f0(\mathbf{q},t)=0$$ with the requirement that $f(\mathbf{q},t)$ be integrable. This expression should look a lot like the total time derivative of some function $F(\mathbf{q},t)$, if...
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about 1 year ago
Comment Post #283985 I'm not sure this is really a question about physics - it seems more like a cultural question.
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about 1 year ago
Edit Post #283957 Post edited:
about 1 year ago
Edit Post #283957 Initial revision about 1 year ago
Answer A: What does Lagrangian actually represent?
There's not really a fundamental interpretation of the Lagrangian because the Lagrangian that describes the dynamics of a system isn't unique - more than one Lagrangian can yield the correct equations of motion. For instance, let's say we have a particle of mass $m$ experiencing a gravitational force...
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about 1 year ago
Edit Post #283502 Post edited:
I didn't expect this answer to be out of date within a week! New paper by Brown & Batygin on Planet Nine's orbital parameters
about 1 year ago
Edit Post #283502 Initial revision about 1 year ago
Answer A: If planet 9 exists, is it correct to say that it is a "dark planet"?
There are perhaps two questions here. The first is whether the planet is intrinsically dark, i.e. it reflects only a small fraction of the light that reaches it from the Sun and emits only a small amount of blackbody radiation. This can be quantified by the planet's albedo, which depends on the compo...
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about 1 year ago
Comment Post #283251 I guess I'm a little confused about one of your criteria ("without . . . acceleration"): in this example, the object should always experience a non-zero acceleration because the $\sim1/r^2$ relation is only 0 at $r\to\infty$.
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about 1 year ago