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  1. R

    Thermo Derivation

    You can just integrate it up I believe. The derivatives in this instance are actually partial derivates if I am not mistaken (the evidence is that Cv is the heat capacity at constant V...which implies that the second term is the change due to volume at constant T). So the total change in S is...
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    How do we know atoms exist?

    I disagree here. One of the primary tasks of the LHC is to show clear *experimental* evidence that protons do in fact have a definite substructure. The math might tell you that its there, but there is no guarantee that the problem is not with the math (especially since our math does have holes...
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    How do we know atoms exist?

    Until the LHC or something experimentally demonstrates that quarks exist I am not necessarily sure that they exist much less that they have or don't have substructure. It could BE that the fundamental particles are simply the things that don't show evidence of decay such as a proton or an...
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    How do we know atoms exist?

    The concept of a dimensionless "point" particle comes from classical physics. That's all I really know for sure. So far there is no experimental evidence of a dimensionless subatomic particle within the nucleus. So the question more or less becomes is SR an approximation? or is it exact, and is...
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    What is this structure?

    Make sure there are 4 bonds attached to each carbon. If there aren't 4 bonds attached to a carbon then "add hydrogens" to that carbon until it has 4 bonds.
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    How do we know atoms exist?

    If we know atoms to be what they are, then we certainly know that they are NOT point particles. Atoms have a 3D shape or volume, they can translate, rotate, and vibrate etc. We also know that these atoms are not the ultimate "smallest" particle of matter as they are built up out of even smaller...
  7. R

    What is this structure?

    The chemical formula you have provided is correct for the number of C's, N's, and O's, but the number of H's is wrong (it is not 21). I don't want to give the name directly because this smells like a homework question...but I can confirm if you have the right formula when you get there.
  8. R

    What is this structure?

    What are you asking for? The name of the structure?
  9. R

    What do 'nerdy' guys like in girls?

    Greatest. Pick up lines. Ever.
  10. R

    Math is beautiful

    OOoh...demoted to GD! Errr...math is beautiful, but the process of learning it is pretty ugly (I say the same thing about physics).
  11. R

    How to learn chemistry?

    Even jokes aren't safe on PF I suppose... Well then, just trust me, chemistry is a fascinating subject if you get a chance to give it a real look at some point. A biologist armed with physics and chemistry would have the tools to make many exciting discoveries as we are going through a...
  12. R

    How to learn chemistry?

    That description sort of reminds me of a community college that I went to for a brief period of time. Fortunately, I didn't attend a chemistry course there.
  13. R

    How to learn chemistry?

    If you are solving the wave function by hand that is likely the case for most of us. This approach isn't needed for chemistry anyways, most energy level diagrams for complex molecules or atoms can be generated directly from spectroscopic data and using normalized wave functions together with...
  14. R

    If a tree falls in the woods

    This question can easily be run around in circles depending on how "sound" is defined, but in general you can say that a falling tree on earth will produce "sound waves" upon falling even if these waves do not carry to a humans ear for a human to become aware that they were made. Note that this...
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    Who's spending the night with Evo? - Again

    Here with my folks and sisters with husbands and my sisters newborns. We are trying to decide on a movie to watch at the moment. The men are trying to compromise with Journey to the Center of the Earth or Leatherheads while the woman are hard lining with the Dutchess (which I will NOT watch...
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    How to learn chemistry?

    Chemistry is built on top of physics. It is more like physics will give you an idea of how chemistry works and not necessarily vice versa. What you get with chemistry is not a tool to help you understand physics at some deeper level, but rather an "expansion pack" that goes beyond what happens...
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    How to learn chemistry?

    theallknower, if you think chemists are just mixing chemicals together without predicting any theoretical consequences or results then you really don't have a clear view at this point of how the ideas in chemical knowledge interconnect. Maybe in the days before such knowledge was available then...
  18. R

    How to learn chemistry?

    It's like Borek and gravenew said, chemists simply have a different focus. Almost the entire subject (sans nuclear chemistry) can be understood by just considering electron movement between atoms. You might be surprised to learn that none of those nuclear particles are necessary to understand...
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    Question about naked swimming at great depth after pressurisation

    Here's a look at the typical size of the swim bladder: The position is usually towards the center of the fish to avoid torque, and the swim bladder (since it can shrink and expand) noticeably adds to the round shape around the fish's "waist"...
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    Question about naked swimming at great depth after pressurisation

    Yes, it is a valid point. I think I read that the vertical limit for a "quick" change in height in the free ocean is about 10 meters or so for most fish...probably much larger than the typical aquarium display. So in an aquarium it wouldn't be much of an issue. Nevertheless, fish still behave in...
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    Characteristic X rays?

    The electrons in each atom are at different energy levels, and as they move between levels they emit photons at different frequencies ("colors"). You don't need X-rays to see this phenomenon, just compare visible light emission spectra for different atoms. You will see that the light appears in...
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    QED: reflection of light in glass

    Hi there eliben and welcome. In this example, the two vectors for the light are pointing in opposing directions (see figure 44 and follow the direction of the light as it travels from the source to either the detector at A or through the glass to will see that 3 to 5 goes up towards A...
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    Question about naked swimming at great depth after pressurisation

    Yes, that's the way they do it. This strategy is not unlike blowing out the oxygen in your lungs when surfacing (the act of blowing out the gas compresses the lung or bladder prior to the expansion that occurs when the remaining gas in the organ expands upon ascent...the net result is the organ...
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    Teen with home chemistry lab mistakenly arrested for meth production

    That student is clearly guilty of unauthorized thinking. His chemistry lab should be confiscated, and his major should be forcibly changed to liberal arts or political science to ensure that such "thinking" never occurs again.
  25. R

    Question about naked swimming at great depth after pressurisation

    Actually the ascent rate has the exact same effect on fish providing the fish have a "gas based" organ such as a swim bladder as their buoyancy organ. This is noticed by fisherman all the time as when they pull up fish suddenly from depths it is often the case that their swim bladders explode...
  26. R

    Query about Sublimation

    The most important issue concerning sublimation is the external pressure on the system. This can be seen on a phase diagram most clearly such as the following for water: Notice that on the...
  27. R

    Please, will you explain the nature of spectral lines

    This was Bohr's contribution. He incorporated at the time "radical" new ideas about quantization (from Plank's quantum explanation of black body radiation) and Einsteins photoelectric effect (E=hv) into a model that could account for the observed line spectrum of a hydrogen atom. Note that the...
  28. R

    Non-dating advice

    A professional chef who cleans the house without being asked? Damn, if he was a woman I'd marry him.
  29. R

    Amplitude of Electromagnetic wave?

    This was found with the photoelectric effect and interpreted by Einstein. It meant that electrons could not be ejected from a metal unless the light was above a certain frequency even if you made the light more "intense." (It used to be thought that energy was proportional to the intensity prior...