Why do photons have no weight? Anything>?>?>?

Question

Photons not having mass

Answer 1

What is the Mass of a Photon?

This question falls into two parts:
Does the photon have mass, after all it has energy and energy is equivalent to mass?

This question comes up in the context of wondering whether photons are really "massless," since, after all, they have nonzero energy and energy is equivalent to mass according to Einstein's equation E=mc2. The problem is simply that people are using two different definitions of mass. The overwhelming consensus among physicists today is to say that photons are massless. However, it is possible to assign a "relativistic mass" to a photon which depends upon its wavelength. This is based upon an old usage of the word "mass" which, though not strictly wrong, is not used much today.
Check out this article:

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

Yours:; Grumpy

Answer 2

That is an excellent question, and nobody is quite sure of the answer yet. It is just observed that photons are massless, and since they have no mass they will have no weight.

Photons are just little quantities of momentum, the stuff of movement. Energy is just that - the catalyst for change. When a photon strikes a particle, like an electron, it makes the electron rebound as if hit. The color of the light (or wavelength of the photon) determines exactly how hard the electron will rebound. From such measurements we can tell that there is no mass to photons.

Answer 3

Ofcourse, no one actually has weighed a photon. But its mass is defined by the special theory of relativity. The mass of the photon is given by:

m = E / c^2
m >< E [c^2 is constant]

so the mass of the photon is directly proportional to the energy it has. Higher the energy, higher its weight.

One must remember that the a photon is a theoratical explination of the composition of light, thus to tie up loose ends such as "What is a photons mass?" or "What is photons energy?", theories have been put forward. Again, they are just Theories, and not neccesarally real.

Answer 4

Photon paths are not bent by gravity. Photons always travel in a straight line.

Because gravity curves space, when the photons move in a straight line the paths look curved. (General relativity)

Since they have no mass, they have no weight (weight is mass in a gravity field).

Why do they have no weight? They're a *wave*. Think of waves as being energy moving through matter. The energy has no material component.

Answer 5

Who told you photons have no mass. They are attracted by gravity. They have a mass equal to the Energy contained in the photon divided by square of the speed of light (c^2)
M=E/(c^2)
The energy contained in the photons (E) is given by h*frequency of the photon, where h equals the planck's constant (approx. 6.626*10^-34)
This is not the rest mass, this is the mass of the moving photon.

Answer 6

Photons have no mass, because relativity says that as you get closer to the speed of light your mass increases, and if they had a rest mass then they would have infinite mass at the speed of light.

But they act like they have mass (they have relativistic mass); they're affected by gravity, etc. For exactly the opposite reason as above, having any relativistic mass (other than infinity) at the full speed of light means they have zero rest mass.

Rest mass / 0 = infinite relativistic mass. Relativistic mass * 0 = zero rest mass.

And physicists usually mean rest mass by just "mass" because relativistic mass depends on speed. (It is the rest mass divided by sqrt(1 - v^2/c^2), where v is the speed and c is the speed of light. You can see that as v approaches c, this expression approaches 0.)

Answer 7

This is an assumption, since they are moving with the speed of light, they cannot have a rest mass, otherwise they would hvae an infinite energy, but they can be attracted by gravity somehow, so they should have some mass characteristics..

Answer 8

Omg everyone's hyperventilating you weight's perfect, your bmi which is how they calculate how much body fat you have in comparison to your height is 21.3 which is right bang in the middle of normal so you have absolutely nothing to worry about your weights fine. 120 pounds is normal it probably would probably be less normal if you started to lose weight.