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# pmb

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1. ## Calculating the hover height of the Harrier jet

This airfoil-based lift - Does it have much affect at, say, 50 feet or 500 feet?
2. ## Postulates with no evidence

There are well-known physicists/cosmologists who are widely published in peer-reviewed journals, and who publish articles which contain postulates which are nonverifiable. It appears to me that that goes against forum policy rules. My question is this: How are we to handle such theories which contain such postulates? If we read such articles and want to discuss them here is it cosidered speculation an has to remain in this forum or if its peer reviewed can we discuss it in the physics forums. I'm refering to physicists such as Alan H. Guth and Paul Davies. See Alan H. Guth et al - http://arxiv.org/abs/0808.3778 -- Journal Reference - (not sure -please see ref) Paul Davies - http://arxiv.org/abs/astro-ph/0403047 -- Journal Reference - Mod.Phys.Lett.A19:727-744,2004
3. ## Gravity equation question.

It's easier to bold the letters. That's what I do. It's soooo much simpler for me and I'm soooo lazy. It looks more like what appears in texts too. E.g. P = m0U p= mv
4. ## Calculating the hover height of the Harrier jet

The Harrier,or any plane like it, can just as easily hover at 50 feet as it can 500 feet. The only difference is the air pressure. All you need to do is calculate the thrust and set that equal to the weight of the Harrier. When these are the same then the Harrier is hovering. Note that the weight is constantly changing due to the fuel burning. So as time goes on the fuel decreases and with that the weight decreases. Pete
5. ## What Physics fact or theory fascinated you the most?

I love relativity. It fascinates me so much that I have spent up to 10 years working on solving a problem. I posted the problem in my website. It's about a rotating magnet. See http://home.comcast.net/~peter.m.brown/em/rotating_magnet.htm I loved working on it. It seemed to be so tricky that people even today are screwing it up. It has to do with the N-machine. This nutcase named Bruce DePalma claimed to have created a free-energy machine. The physics was rooted in a rotating magnet. He didn't have a good grip on relativity, perhaps no grip at all as a matter of fact. It was related to the Homopolar generator - which is hard to find in physis texts. I know of only one text that toiuches on it and its an SR text by Shadowtz. The nonsense goes on. I'm reminded of something I read in a college course I took called Philosophy of Science. One of the texts was Science & Unreason, by Radner and Radner. In the Preface it reads And I've found that to be very true over the last two decades. This rotating magnet is one example that comes to mind. The SR text I mentioned above is Special Relativity by Albert Shadowitz, Dover pub (1968). See page 126. The topic is called the Faraday disc or homopolor polar generator. If anybody wants I'd be more than happy to scan it into a PDF file and place it on my web page for all to read. There are references in the American Journal of Physics.
6. ## Do photons carry/contain more than just energy, momentum and angular momentum?

I guess I'll have to stop being lazy and do the work. I think it'd be good to do the work here. It'd be a good way to refresh my memory of how to do Latex. That will come later this week (weekend) or next week ... or .. today. Yikes!
7. ## Do photons carry/contain more than just energy, momentum and angular momentum?

I'm too lazy to do the work but I do recall that the stress-energy-momentum tensor for a EM wave traveling in one direction has a non-zero stress component. If my memory is correct then wouldn't that be the answer to Do photons carry/contain more than just energy, momentum and angular momentum? or would the stress component just be part of the angular momentum, if an EM wave has angular momentum? Let's consider a sinusoidal wave movingin the x-direction, i.e. E_z = E_0 * sin( x - wt) where E_0 = a number whose value is the magnitude of the maximum value of the electric field.
8. ## Definition of "Classical Mechanics"

There were some points which I shouldn't have made being that tired and then , on top of that, commenting on things I have zero interest in - Mix them together and we have bad juju At this point I lost interest (I actually had nothing more to say after my first opening post. Since there's too much other work to do this will be my point of exit. Thanks. Note: I will say one last thing before I sign off this thread. When I started this thread it to get an idea of how many people use/interpret the term Classical Mechanics to include relativistic mechanics as Goldstein uses/defines it.
9. ## Active vs Passive Gravitational mass

Oy! Of course. I had this sinking feeling in the pit of my stomach as to the V_i and I couldn't resolve it. Thanks elmotat! Problem solved!
10. ## Active vs Passive Gravitational mass

To what end? The system I was considering is a system of three interacting particles. What would you use your Lagrangian for?
11. ## Idea about particle physics

Smaller particles? What does that mean? Smaller than what? The term "particile" often means a point particle which means that they have zero spatial extent. For this kind of particle there is nothing smaller. An electron is such a particle. Same with the photon and neutrino, graviton etc. Right. The graviton. Scale? What do you mean by that term in this context? Atoms don't contain gravity particles.
12. ## Definition of "Classical Mechanics"

I don't know what "is really" means. Is it anything like Israeli? Classical Mechanics is a system which is based on Newton's laws. If the Galilean transformation is employed to transformed between inertial frames then we have what I refer to as Classical Newtonian Mechanics (for lack of another term) and when we use Lorentz transformations we have SR. When we add to this like equivalence principle etc the we have GR. That's my definition and how precise it is depends on its applications, not the definition. And that's they way PMB seems it. ajb - What does this hand waving thing you mentioned have to do with anything? Take a look at Goldstein et al's text and notice how everything they've derived is rooted on Newton's three laws which have a very small explicit mathematical content it them. Lagrangian and Hamiltonian mechanics can be deduced from those laws as can the rest of classical mechanics. Awww shucks! I did it again! I got into a discussion about a definition without being aware of it that much. I sure can be slow in the noggin at times.
13. ## Definition of "Classical Mechanics"

I'm sorry but I don't understand, why the need to make it so complex in your other post? It's just so much easier to say that Classical Mechanics is physcs which is outside of quantum mchanics? Everyone woiuld know what you meant. This thread was supposed to be about what you think Did you interpret "precise" to mean that I was asking about something more complicted than Perhaps I didn't state the question so as I'd get the type of response I was looking for. I was looking for a non-mathematical definition of "classical mechanics".
14. ## Definition of "Classical Mechanics"

I wish I knew what you were talking about. You're describing this in some way that I don' recognize. It seems that what you wrote could also be interpreted as quantum mechanics. Can you restate it so that it makes moe sense to me? I.e. please dumb it down for me. It seems to me to be a theoretical statement of the physics of something but I can't put my finger on it. I've learned a lot in the last 27 years and there's no way I'll ever remember all of it no matter how much refreshing I do.
15. ## Is Philosophy crap?

PI'd find it difficult or perhap impossible to do physics without philosophy. Philosophy is that part of your thinking whereupon you come to ask yourself or Can anytrhing in physics be said to be true? How do I know what I know? etc. I participated in a similar discussion in this ScienceForum today. One of my favorite quotes was raised. There is a text out called Classical Charged Particles Third Edition by Fritz Rohrlich, World Scientific Publishing (2007). Rohrlich is a well-known, first rate physicist. Chapter 1, which starts on page 1, is called Philosophy and Logic and Physical Theory. In the first paragraph the Rohrlich writes I agree. Do yourself a good one and read the following books Another text is Logc of Scientific Discovery by Karl Popper, Routledge Classics. First Ed. published in 1935 - Awesome book! This book is legendary! A must read for a very good philosopher in physics. Another awsome text is called The Structure of Scientific Revolutions - Third Edition by Thomas Kunn. as well as chapter one of Rohrlich's text I quoted above. After that you'll understand what people mean when they stress the importance of philosophy in physics. You might just find that you've been doing a lot of philosophy and not knowing it. There is another good book http://www.amazon.com/Practical-Logic-Antidote-Uncritical-Thinking/dp/0155030361/ref=sr_1_4?ie=UTF8&qid=1324334182&sr=8-4 Great book!!! Especially if you want to more easily win those arguments in wqhich you are right.
16. ## Why does k vary in Coulomb's law depending on the medium?

Nice response! That's my thought too, except I couldn't think of how to put it as elegantly as you have.
17. ## Definition of "Classical Mechanics"

I agree with you. However I don't believe that others won't. Hence this thread. I'm not sure what you mean. That could be taken to mean non-relativistic mechanics (a) = Newtonian non-relativistic mechanics (b) = Quantum Mechanics I think this is where some disagreements will tend to rise.
18. ## Is physics and philosophy a worthwhie course?

I myself have a BA in Physics and Mathematics from Merrimack College, North Andover MA. I took a course called The Philosophy of Science which I loved. The text that they now use in the course is Scientific Inquiry; Readings in the Philosophy of Science Edited by Robert Klee. It seems like a good text. I haven't gotten around to reading it yet. Another text is Logc of Scientific Discovery by Karl Popper, Routledge Classics. First Ed. published in 1935 - Awesome book! This book is legendary! A must read for a very good philosopher in physics. Another awsome text is called The Structure of Scientific Revolutions - Third Edition by Thomas Kunn. There is a text out called Classical Charged Particles Third Edition by Fritz Rohrlich, World Scientific Publishing (2007). Rohrlich is a well-known, first rate physicist. Chapter 1, which starts on page 1, is called Philosophy and Logic and Physical Theory. In the first paragraph the Rohrlich writes I fully agree with Rohrlich, that's for sure! I you want to read the first chapter than I can arrange that. Just PM me. This chapter,or its equivalent, is a must read for physicists who wish to be considered top rate too. Again, in my opinion. On page 2 the author writes There is a text out called Classical Charged Particles Third Edition by Fritz Rohrlich, World Scientific Publishing (2007). Rohrlich is a well-known, first rate physicist. Chapter 1, which starts on page 1, is called Philosophy and Logic and Physical Theory. In the first paragraph the Rohrlich writes I fully agree with Rohrlich, that's for sure! I you want to read the first chapter than I can arrange that. Just PM me. This chapter,or its equivalent, is a must read for physicists who wish to be considered top rate too. Again, in my opinion.
19. ## What does tag = Meson mean?

Every time I post something the term Meson appears to the right inside my post. What does it mean?
20. ## Definition of "Classical Mechanics"

I don't see anything wrong with it in principle. In practice, in this website it might just be a pain in the butt foor no real gains. As mentioned above, relativiy is a subcategory of classical phyics. Quantum mechanics would be a different branch of physics than classical mechanics. I should make it clear that the only reason I created this thread was to create awareness regarding what people mean when they use the term classical mechanics. It can lead to confusion. I have vague recollections of that happening in the past in physics forums on internet forums.
21. ## Definition of "Classical Mechanics"

I was wondering if anyone here has heard of the definition of Classical Mechanics which is defined in the well known, staple of classical mechanics Classical Mechanics - Third Edition by Goldstein, Safko and Pool, Pearson Education, Inc,. Publishing as Adison Wesley (2002). See page1, first paragraph I have, for the longest time, used this text, and as such this definition for classical mechanics. So if you see me use the term you can be certain that this is what I mean. But I certainly can't assume that this is what others mean by it. I'd like to make a request of you good folks to state the definition of classical mechanics as you choose to use the term, especially when knowing the precise definition ot it is critical. Thank you all. Pete ps - If we were to take Goldstein etc. literally then the relativity forum would have to be absorbed into the Classical Physics forum. I think that'd be getting carried though.
22. ## Active vs Passive Gravitational mass

Yes! Excellant! Thank you!
23. ## Elements

Great granpa! The reference is what I was asking for so thanks for the reference/link so thank you very much! When I have more time I'll have to read that in detail. I'm curious as to the purpose of what the OP was looking for. E.g. does such a superatom exist for all elements etc
24. ## Earth Hole

If the hole was depressureized then a person in freefall would not be able to tell if he was in free-fall in a gravitational field or at rest in an inertial frame of reference since, according to the Equivalence Principle, they'd be the same. At best the person in free-fall could carry instrumentation in which was sensitive enough detect the gravitatidal forces in his frame. No person can detect such a small variation in the gravitational field.
25. ## Active vs Passive Gravitational mass

I had a feeling that was the case. No harm done. I'm going to try it in Newtonian mechanics first and then relativistically later. I'll share the intermediate results with you if you'd like? In all likeyhood I'll have some help from experts on the subject along the way. In first term it seems as if you'er using Einstein's summation convention but in the second term it doesn't appear that way. Confusing! Ya have to be sure when it comes to things like this. For example; Let's consider the system at hand. We have a three particle system moving in the z = 0 plane and therefore V_3 = Vz = 0. The kinetic energy of the system T is given as found to be $T = \frac{1}{2} m_1 |\bold{\dot{x}}_1|^2 + \frac{1}{2} m_2 |\bold{\dot{x}}_2|^2 + \frac{1}{2} m_3 |\bold{\dot{x}}_3|^2$ The general potential for a multi-particle system is derived in Classical Mechanics - 3rd Ed., Goldstein, Poole and Safko on page 11 and is found to be $V = \sum_{i} V_{i} + \frac{1}{2}\sum_{ij} V_{ij}$ We can now state the full Lagrangian (without active/passive mass terms) $L = T - V = \frac{1}{2} m_1 |\bold{\dot{x}}_1|^2 + \frac{1}{2} m_2 |\bold{\dot{x}}_2|^2 - \sum_{i} V_{i} - \frac{1}{2}\sum_{ij} V_{ij}$ where i does not equal j in last summation. I haven't got this Latext thing down. I was fluent a while back but their Latex thingy shut down and since then my Latex became atrophied. Now! The trick is to formulate this in terms of active and passive g-mass. That I don't know how to do. I may figure it out. That takes time. Sometimes the answer just pops into my head. I love it when hat happens! Thanks, Pete
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