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Everything posted by Autumn_Man

  1. Only to people who don't know what the term proper means. In this context the term proper means intrinsic. Proper mass is defined as the m in E^2 - (pc)^2 = m^2c^4. Until students learn what the terms mean who cares what mistakes they make. Mistakes are cleared up when the student learns the physics. Bad students believe all sorts of weird things "we" is what is found in the literature and "we" understand and use the term proper mass or rest mass too when that is the subject
  2. On the particle point of view the relativistic mass of a photon is finite and has the value m = p/c = E/c2at all times. The proper mass or a photon is zero at all times. When it comes to the invariant mass of disordered radiation there is a zero-momentum frame of the radiation and when there is energy and a zero momentum frame the invariant mass of that radiation is not zero. Tjhe invariant mass of a system of particles is defined the same way as proper mass is only with E replaced by the sum of all energies of the particles and p replaced by the sum of all 3-momentun of the particles.
  3. I hate to be the one to tell all of you that the Earth isn't round. It's spherical.
  4. You're confusing freedom of speech as it pertains to our constitutional rights and as it pertains to our private lives. It doesn't hold in all wallks of life either. Freedom of speech is not absolute in the US. In particular you don't have freedom of speech when it comes to libel, slander, obscenity, copyright violation and incitement to commit a crime. You also can't go into a private organization and start preaching whatever is on your mind. In this case you can't go to a private discussion forum such as this and not follow the rules the've established to keep order to the place. You can't g
  5. A better term than rest mass is proper mass. It has no conotations about being measured in a rest frame. It's an intrinsic property of a particle and can be calculated using energy ann momentm by the relation (letting m = proper mass) E^2 - (pc)^2 = m^2 c^4. Solve for m and you have the proper mass of any particle as determined from any frame of reference.
  6. It depends on what terms you wish to express the momentum in. As you said above, m = p/v therefore p = mv where m is the relativistic mass of the body, not its rest mass. Sorry but I don't understand all that. Can you be clearer? The problem here is that you're confusing rest mass with relativistic mass. The problem is obvious, isn't it? He's talking about relativistic mass and you're talking about rest mass. The rest mass of a photon is zero and its relativistic mass is E/c2
  7. I think that the Big-Bang started the whole process by sending out a huge amount of energy at an event billions of years ago. It used to be believed that it was the momentum of the explosion that is carrying matter away but lately astrophysicists and cosmologists have discovered that the expansion is occuring at an accelerating rate. That can be due to various reasons such as the presense of a positive cosmological constant (which is more of an description than an explanation). Another reason would be negative pressure. Such sources act as negative active gravitational mass and is thought of a
  8. The name Principle of Least Action is a misnomer. Its more accurate to refer to it as the Principle of Stationary Action since all that is required is that the first variation vanish. Think of the analogy with normal functions. We consider here functions that are defined and continuous on open intervals. If the first derivative of a function is zero at a point then there is either a maximum, minimum or extremum at that point. If the second derivative of the function at that same point is positive then the function is a minimum at that point. If its positive then it’s a maximum and i
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