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Seems about right! :) I don't know what you're wanting to do (are you an engineer, is this a hobby, etc.?) but another good resource is the Feynman lectures Vol II - http://www.feynmanlectures.caltech.edu/II_01.html You can't really dip in and out of them - it's probably best to make time to...
2. Angular momentum of a rotating door

Ah, of course. No, it's definitely not rotating about S. Thank you. Also realise now that the definition of the intertia tensor only involves motion about the centre of mass, so obviously it doesn't take the angular momentum relative to the origin at $S$ into account. So then I get this- that...
3. Angular momentum of a rotating door

Why aren't the two the same? Surely the whole system is connected and therefore has the same $\omega$
4. Angular momentum of a rotating door

Ah no, sorry - it should be $L$ . This was part of a final year exam question, so I'm pretty sure I must be wrong somewhere!
5. Angular momentum of a rotating door

Homework Statement A door ( a rod of length $L$, mass $M$) rotates with angular velocity $\omega$ about a point $H$, and approaches a stop at $S$. $H$ and $S$ are along the same line, and separated by a distance $s$. Show that the angular momentum of the door about the point...
6. Rayleigh Criterion Question

Homework Statement 'A scientist wants to take a picture of a distant yellow object using a pinhole camera such that the picture is of maximum sharpness. Let $\lambda$ =wavelength of yellow light, $d$ = diameter of pinhole, $D =$ distance of pinhole to film. Find $d$. Homework...
7. Torque question (qualitative)

I'm not sure what level of explanation you want... Most simply, torque is a turning moment. The idea of torque is that if you apply a force at a greater distance, you get a bigger rotation - it would be easier to swing a cat by its tail than its middle (if you wished to swing cats), and it...
8. Plane Wave at Barrier

Homework Statement Sorry for the dull question. Problem is as shown/attached Homework Equations The waves in part ii) are travelling in a HIL dielectric of permittivity $\epsilon_{r}$ from $0 <z<d$ and then hit an ideal metal boundary at $z=d$. The Attempt at a Solution I figure this...
9. Stirring a Cup of Tea

The change in entropy of the surroundings is zero? Like I said above? Or, from equation (1) since the surroundings are a heat bath, there is no change in temperature, therefore no change in entropy...? Phase rule makes sense, had to look it up -$F= C-P+2$ - in this case, $C=1$ (assuming...
10. Stirring a Cup of Tea

That's what they put in the question! I'm assuming that the work went out as heat into the surroundings when the tea cooled?
11. Stirring a Cup of Tea

Also - regarding the point about entropy and state variables. Is there an intuitive justification of the fact that any given state variable $S,U$etc., can be written explicitly in terms of only two variables i.e $S=S(T,P)=S(V,N)$ or do I need to start doing some more theoretical...
12. Stirring a Cup of Tea

Ah, I see. I'm guessing you're wanting me to say the $dS=0$ - since the temperature of the tea at the end will be the same as the temperature at the beginning. I guess that makes sense for the tea - like I said earlier, it seems sensible that the tea loses all the extra internal energy it...

28. Energy in a Stationary Wave

Yes, but a stationary wave is by definition formed from two travelling waves moving in opposite directions which means it can then be rewritten in the form that you suggest with the time and space separated? Or is that not right?
29. Energy in a Stationary Wave

Homework Statement Show that the potential and kinetic energy densities for a stationary wave are not equal. Homework Equations A) The 1-D Wave Equation: $$\frac{\partial^{2} \psi}{\partial x^{2}} = \frac{1}{v^{2}} \frac{\partial^{2}\psi}{\partial t^{2}}$$ B) The general form of a stationary...
30. Why, IF electrons really orbited atoms, would they lose energy?

Oh right, for sure. The electron is at a different distance from the point! Sorry!