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How much does the photon weighs?
Can you explain litlle bit more please?russ_watters said:A photon has no mass. "weight" doesn't apply.
Oops - I knew that. :grumpy:chroot said:Photons do not have mass, but they do have energy. Energy couples gravitationally in the general theory of relativity, and thus light does have weight. A box full of light actually weighs (very slightly) more than an identical empty box.
- Warren
Clausius2 said:What happens?. How can I calculate the limit when v-->c and m--->0?
theFuture said:Consider m^2c^4 = E^2 - (pc)^2 where m is the rest mass. A photon has no rest mass, so E=pc. This allows you to talk about the energy and momentum of photon.
But for relativistic momentum ¡t is not obvious.
I don't believe the weight of a photon is a well defined quantity in that different people mean different things by the term weight of a photon. Normally the term "weight" refers to the force required to support an object in a gravitational field. I suppose you could say that the gravitational force on a photon is the "weight". But I personally stay away from that kind of definition myself.tumor said:How much does the photon weighs?
By "a photon has no mass" it is meant that the proper mass of a photon is zero. However a photon has inertial mass (aka "relativistic mass" which is has due to the fact that a photon has momentum), active gravitational mass (due to the fact that light generates a gravitational field) and passive gravitational mass (due to the fact that light is deflected in a gravitational field). Keep in mind the famous experiment by Pound and Rebka on gravitational redshift. The paper they wrote on this topic was entitled "On the Weight of Photons". Also recall Lev Okun's paper "The Concept of Mass" that appeared in Physics Today in June 1989. In that paper Okun calculates the gravitational force on two photons moving in a Schwarzschild field, both in the radial direction and the horizontal direction. Okun concludes ..., a horizontally moving photon ... is twice as heavy."russ_watters said:A photon has no mass. "weight" doesn't apply.
For a calcultion which demonstrates that a box of photons weighs more than the same box with no photons in it see the paper "On the concept of mass in relativity" which is listed at http://www.geocities.com/physics_world/turin said:Or you may be thinking of radiation pressure. This is caused by an impulse that a photon imparts to an object upon reflection or absorption.
The weight of an object is a well defined quantity in physics as well as in general relativity. I like the following definition. Its what people use the most and its quite reasoable. From The equivalence principle and the question of weight, Kenneth Nordtvedt, Am. J. Phys. 43(3), March 1975JohnDubYa said:Weight is a layman's term, not a scientific term.
The weight of a body is meant to be the force (e.g., the compression of a spring scale) required to either support the body in a gravitational field (gravitational weight) or to accelerate the body relative to inertial space (inertial weight).
The most rigorous definition of momentum is found by the implicit rule for defining (relativistic) mass. I.e. mass, m, is defined such that the quantity mv is conserved. The quantity mv is then defined to be the momentum. The relation p=mv/[1-(v/c)^2]^(1/2) is derived by assuming the particle can travel at speeds less than c (i.e. its derived only for tardyons). If you want to express the momentum in terms of energy then its E = pc, which is derived using Maxwell's equations. It then follows that m = p/c. If you want to express it in terms of mass then defined m = E/c2.Clausius2 said:Talking about this, when I saw for the first time the Einstein momentum formula for relativistic dynamic:
p=mv/[1-(v/c)^2]^(1/2)
I wondered what happens with photons:
v=c and m=0, so It is not determined.
pmb_phy said:The most rigorous definition of momentum is found by the implicit rule for defining (relativistic) mass. I.e. mass, m, is defined such that the quantity mv is conserved. The quantity mv is then defined to be the momentum. The relation p=mv/[1-(v/c)^2]^(1/2) is derived by assuming the particle can travel at speeds less than c (i.e. its derived only for tardyons). If you want to express the momentum in terms of energy then its E = pc, which is derived using Maxwell's equations. It then follows that m = p/c. If you want to express it in terms of mass then defined m = E/c2.
Pete
A photon is a massless particle, meaning it has no weight. It only has energy and momentum.
No, because a photon has no mass, it cannot be weighed in the traditional sense. It can only be measured by its energy and momentum.
A photon's weight cannot be measured in traditional units like kilograms or pounds. Instead, it is measured in energy units such as electron volts (eV) or joules (J).
The weight of a photon can be calculated using Einstein's famous equation E=mc², where E is energy, m is mass, and c is the speed of light. Since the speed of light is a constant, the mass of a photon will always be zero.
Currently, there is no evidence to suggest that a photon can have weight or mass in the future. However, our understanding of physics and the universe is constantly evolving, so it is possible that new discoveries may change our understanding of photons and their properties in the future.