Relativistic Mass

Back to Physics World


Proverbs 11:1 - The Lord abhors dishonest scales, but accurate weights are his delight.


For the definition of relativistic mass see Inertial Mass, which is identically the same thing.


Textual Examples

Relativity: Special, General and Cosmological, Rindler, Oxford Univ., Press, (2001), page 120

According to Einstein, a photon with frequency n has energy hn /c2, and thus (as he only came to realize several years later) a finite mass and a finite momentum hn/c.

From Introducing Einstein's Relativity, Ray D'Inverno, Oxford Univ. Press, (1992), page 50

Finally, using the energy-mass relationship E = mc2,, we find that the relativistic mass of a photon is non-zero and given by

m = p/c.

Combining these results with Planck's hypothesis, we obtain the following formulae for the energy E, relativistic mass m, and linear momentum p of the photons:

E = hf             m = hf/c2            p = hf/c

Special Relativity, A. P. French, MIT Press, page 20

Let us now try to put together some of the results we have discussed. For photons we have

E = cp

and

m = E
/c2

(the first experimental, the second based on Einstein's box). Combining these, we have

m = p/c


Journal Examples

Apparatus to measure relativistic mass increase, John W. Luetzelschwab, Am. J. Phys. 71(9), 878, Sept. (2003).

Relativistic mass increase at slow speeds, Gerald Gabrielse, Am. J. Phys. 63(6), 568 (1995).

In defense of relativistic mass, T. R. Sandin, Am. J. Phys. 59(11) 1032 (1991).

A simple relativistic paradox about electrostatic energy, Wolfgang Rindler and Jack Denur, Am. J. Phys. 56(9), Sept. (1988).

An elementary development of mass-energy equivalence, Daniel J. Steck, Frank Rioux, Am. J. Phys. 51(5), May (1983).

Observed Relativistic Mass Increase for 0.3 eV Electron, G. Gabrielse and H. Dehmelt, Bull., Am. Phys. Soc. 25, 1149 (1980).

Mass & Energy - by Q. ter Spill, Institute of Physics Education


Specific Instances - Not Used Throughout Text

Gravitation, Misner, Thorne and Wheeler, W.H. Freeman & Co., (1973), page 141.  Proof that stress-energy tensor is symmetric

Calculate in a specific Lorentz frame. Consider first the momentum density (components Tj0) and the energy flux (components T 0j). They must be equal because energy = mass ("E = Mc2 = M")

T j0 = (energy flux)

= (energy density) x (mean velocity of energy flow )j

= (mass density) x (mean velocity of mass flow )j

= (momentum density) = T 0j

Cosmological Principles, Peacock, Cambridge Univ. Press, (1999).

From page 18

When dealing with mechanics, however, we have not one conserved quantity, but four: energy and vector momentum. So, although Jm is a perfectly good 4-vector mathematically it is not physically relevant for describing conservation laws involving mass. For example, conservation laws involving Jm predict that density will change under Lorentz transformations as r --> gr, whereas the correct law is clearly g2 (one power of for change in number density, one for relativistic mass increase.

From page 17-18

The only ingredient now missing from a classical theory of relativistic gravitation is a field equation: the presence of mass
must determine the gravitational field. [...] Now, if this equation is to be covariant, T
mn must be a tensor and is  known as the energy-momentum tensor (or sometimes as the stress-energy tensor). The meanings of its components in words are T00 = c2x(mass density) = energy density, T12 = x-component of current of y-momentum etc. From these definitions the tensor is readily seen to be symmetric. Both momentum density and energy flux density are the product of a mass density and a net velocity, so T0m = Tm0.

A First Course in General Relativity, Schutz, Cambridge Univ. Press, (1990). Page 94

One final note: it is clear that

(4.6)    N*N = n2,   n = (-N*N)-1/2

Thus, n, is a scalar. In the same way that 'rest mass' (a.k.a. proper mass) is a scalar, even though energy and 'inertial mass' are frame dependant, here we have that n is a scalar, the 'rest density,' even though number density is frame dependant.

A Short Course in General Relativity, Foster & Nightingale, Springer Verlag, (1994). Discussing light climbing out of a gravitational field

Then in traveling from the emitter to the receiver a photon suffers a loss in "intrinsic" energy equal to its gain in gravitational potential energy. The loss in intrinsic energy is h(nE - nR), while the gain in gravitational potential energy is

phy-eq-01.gif (1277 bytes)

on assigning the mass hnE /c 2 to the photon. Equating these leads to the fractional-shift formula (4.17). This formula assumes that the photon's energy has both inertial mass and gravitational mass, and depends in an essential way on the equivalence principle.

The Evolution of Physics, Einstein & Infeld, Touchstone Pub., (1966). Commenting on the observation made by an observer inside an accelerating elevator that light is ‘weightless’ Einstein

But there is, fortunately, a grave fault in the reasoning of the inside observer, which saves our previous conclusion. He said: “A beam of light is weightless and, therefore, it will not be affected by the gravitational field.” This cannot be right! A beam of light carries energy and energy has mass.


University Lecture Notes - Online Examples

From Second INTERNATIONAL GIREP Seminar on Quality Development in Teacher Education and Training, 1 - 6 September 2003 University of Udine, Italy. -- Ambiguities in Teaching Physics: The case of weight and Energy-Mass

We think that, all three opinions are equivalent with one another, except in the cases where their supporters pretend to prove the priority of one opinion upon another, or, in the worst cases, to proclaim other opinion/s as wrong, even when these opinions are formulated or stated by Einstein, Heisenberg, Feynmann or Hawking.

Syracuse University: Special Relativity - Lecture 16 , Lecture 17

The Special Theory of Relativity - J D Cresser, Department of Physics, Macquarie University

Washington State University - Einstein and Relativity

Michael Fowler - University of Virginia

Keith E. Holbert - Relativity notes - Arizona State University

Relativity - University of Chicago

University of Durham

Relativistic mass and dynamics - Royal Holloway, University of London

Ohio State University at Lima

Special Theory of Relativity - Florida State University

Physics 110 - Astronomy Dept. U. Washington - &quoot;But the most honest answer to your question is yes--light has mass."


Particle Accelerator Labs

CERN - The Cyclotron

The real limiting factor is the basic design – all particles must orbit at the same frequency, whatever their speed. As particles approach the speed of light, however, they behave as if their mass is increasing. Accelerating them becomes more difficult and they start to lag behind the oscillating electric field. As cyclotrons approached 20 MeV they began to reach their limits and a new design had to be produced.

Argonne National Laboratory

Lawrence Berkeley National Laboratory

University of Wisconsin-Madison


Other

Dr. Greg Snow - University of Nebraska

Physics Today - Concepts of Mass in Contemporary Physics and Philosophy - Mass Jammer

Statistical Physics  - Kip Thorne - Inertial mass per unit volume

What is mass? - by R. I. Khrapko, Physics - Uspekhi, 43 (12), 1267 (2000)


Back to Physics World

Hosted by www.Geocities.ws

1