sethoflagos

I've just done it. According to your earlier definition: A more interesting question would be to ask "How was the exhaust decelerated from v to v - ve?" One for another day perhaps.

Yes, mdv/dt = -vdm/dt is indeed the overall force balance. So let's separate rocket from exhaust components. Consider an observer travelling with a constant velocity v He sees the rocket of mass m gain a velocity dv. He sees a small amount of mass dm ejected at a velocity of ve in the opposite direction No nett motion of the total becomes mdv = -vedm Hence we recover your thrust equation mdv/dt = -vedm/dt It really isn't rocket science ..... er 🤨

Someone gives you $5. Someone takes $5 off you. You are left with $0. Someone gives you $5. Someone takes $5 off you. You are left with $0. Neither did I mention that integration of the equation yieds the Tsiolkovsky rocket equation. The OP didn't ask for it. But you can mug up on it at https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

So? What is omitted that is pertinent to your OP?

dp/dt gives you BOTH sides of the equation dp/dt = d(mv)/dt = mdv/dt + vdm/dt =0 Hence: mdv/dt = -vdm/dt

edit: deleted

I'm inclined to see even this as a false dichotomy. I like Aristotle's ancient maxim: 'Nature operates in the shortest way possible'. It keeps coming back in various guises: the various statements and restatements of Occam's Razor; Principles of Parsimony and Least Action; even the simple symmetries underpinning the Standard Model. In context, it is indifferent to any concept of supernatural being. Why should a principle that frames much of your core opinions be framed in terms of something you've rejected? Do we label modern chemists as 'antiphlogistonists'? At some stages in our development, explanations involving supernatural beings were the simplest and therefore the best explanations going. But we have better explanantions available to us now and are able to discard some of the more elaborate beliefs of our ancestors. So like @Genady I find the term 'atheist' unhelpful though I stopped believing in fairies nearly 60 years ago. I feel the term is maintained in the interests of those who wish to keep an outdated concept centrestage. Time to move on.

I see scattering as a perfectly elastic exchange of momentum with no energy exchange. ie. the scattering body changes direction without a nett change in speed and no heat transfer. Ditto the photon so there is no change in frequency and no spectroscopic impact (other than directional). Photon absorption processes are quite different though since there is a transfer of energy into the absorber and unless the photon is reemitted very quickly, the increase in internal energy must have a thermal impact. So yes, I agree with @swansont on this point. Yes indeed. if the photon is energetic enough to start shunting electrons into different orbitals then the physical nature of the particle starts changing. But most of the gases I've worked with don't absorb in the optical range so it's not something I've ever had to worry about.

I enjoyed that little read. Thanks! I'd actually guessed Jack Vance from your storyline. It had a bit of an Eyes of the Overworld feel to it.

Bear in mind that there is a dynamic equilibrium between translational, rotational and vibrational components. Compression for example is a direct input of translational kinetic energy, but it it gets partitioned equally between all the degrees of freedom as part of the equilibriation process. If you look at purely the translational modes, the monatomic gases always behave elastically, but other gases only appear elastic on average.

Point understood. A waveguide that can fit into a pea restricts the emitter to W-band or higher. Such wavelengths do not penetrate more than skin deep. Not much use for defrosting purposes.

Without stating it directly, you are making enquiries about an em band that is used primarily for military applications (see https://en.wikipedia.org/wiki/W_band) I reported the thread because I am uncomfortable discussing this technology in detail given the current world situation.

Can I please ask that members not post to this thread until the mods have addressed the report I've raised to it. Thanks in advance for your cooperation.

The size limitation would I think enforce a waveguide selection sized for something in excess of ~75 GHz. What kind of application do you have in mind?

Much appreciated. Thank you.

Remember that engineers and physicists employ a double negative on the work term by a change of both sign and sense. It still works, but we have to remember the correct sign convention in all applications where the work term arises. Someone with an odd turn of mind could paraphrase the 'unchemist' version as delta U = heat - unwork. In principle one could apply this double negative process to all three terms and get delta Cold = cool + unwork. It's not really unphysical, simply perverse. Just as absolute U cannot be -ve, absolute Cold could never be +ve. It could work in principle but it would only serve to add confusion to the world. Which I'm guessing is the OPs intent.

Deleted comment

This is a thoughtful and well-written post. Thank you. Does the truth hurt? Only if you allow it to maybe.

By the age of seven, I'd developed a deep interest in geology and palaeontology and started reading every book on these subjects I could lay my hands on. This inevitably led to the question 'Why are all the adults I know lying to me?' Not nature or nurture. Just logic.

Which made you the first person I ever put on my Ignored Users List. And that's despite being largely sympathetic to your political position. I don't question your behaviour particularly, but it does make me wonder what you're trying to achieve.

This story is probably entirely fictitious, though I am acquainted with the individuals involved. A 'Johnnie Just Come', let's call him Kevin, was introduced to Lagos with a visit to the notorious Club 69. After a short while, the 'shop steward' of the female patrons asked him if he'd like the company of one of them. Kevin replied that he wasn't interested as he was gay. "But there are no gay Nigerian men. How are you going to manage?" "Prayer and cold showers" replied Kevin. Ten minutes later she returned with a guy in a pink shirt in tow. "I thought you said there were no Nigerian gays" "He's from Ghana" Bottom line (no pun intended) is that if there is a demand for a service, the market will provide it irrespective of any third party tutting and expressions of disgust. Which suggests that the tutting and expressions of disgust are no more than posturing.

I didn't know. One of my uncles was deaf from birth (rubella). He was very kind to me, taught me loads about river and lake fishing and so on. It's always grieved me that I was never able to return his kindness in full simply because I had no fluency in sign language and could only thank him with a smile. It may well be that it is 'incumbent' on those with disabilities to adapt to the world around them, but does the world around them have no duty to adapt to their disabilities? I hope not. Perhaps that is why I feel no urge to return to the UK under the present regime. From where I am, it simply appears inhumane.

Wise words. But what if you don't understand how the listener may interpret the style? Bear in mind that within a group focussed on the sciences, there is the possibility of interacting with some ASD spectrum affected indivividuals who really have a difficulty in comprehending the POV of others.

This really is an important point. However, consider what happens when you leave academia for the 'real' world. The majority of my written output for the last 40 years or so has been defence of contractual position or more recently, technical legislation. The wording is typically 'impersonal' but corresponds to what I understand to be 'passive aggressive' in today's vocabulary. Maybe it's the focus on the difference between 'should' and 'shall'. I don't know. I've been accused of this a couple of times but I don't fully understand what it means. All I can say is that there is never any conscious malice behind it, it's just the way I write stuff. I didn't say that I 'cared'. 7 billion people in the world and a few don't like me. So what. I said I was 'just curious'.

I'm actually quite uncomfortable with the 'pontificating' side of this equation unless I really am sure of my ground. I served my apprenticeship in a West Yorkshire paper mill which was a fairly brutal working environment by anybody's standards. To carve out a career in such circumstances necessitates a good appreciation of the strength of your position and the ability to defend it robustly when required. This isn't something that came naturally to me. Just force of circumstance. Later in my career, serving typically as lead process engineer, I respected the judgment of the leads of the other engineering disciplines in regard to their own specialist fields as they respected mine. Within my discipline, I had to accept sole responsisibility for the group's performance and therefore instructed my discipline team on how we were to proceed. Not a democracy. Arguably a meritocracy. I did listen to whatever my group had to say but the bottom line was that I had final word. And anyone who couldn't live with that had to live with the inevitable consequences. I'm conscious that some of that 'dictatorial' past may leak out in some of my postings. I hope not too much.