weight of sunlight ?

[fatgaz]

i was in a quiz last night and a question came up "how much does all the sunshine beating down on the earth weigh - ocean liner, flea, or nothing i answered nothing,correct answer was ocean liner. Now my question is :- How do you measure the WEIGHT of light ???

[mjd]

The short answer is that light does not have any mass and does not weigh anything.

[gen2]

I think the confusion here lies in the distinction between mass and weight. You are correct to say that a photon has zero mass. Weight is caused by the pull of gravity on something and light IS affected by gravity. A black hole for example pulls all light back into itself. Light passing a massive object is refracted. Maybe this is the source of the calculated weight given in the question.

[gen2]

Another possibility hinges on the interpretation of the word 'sunshine'. If it said 'sunLIGHT' then what has been stated above is correct, but 'sunSHINE' could include the extras - the charged particles called the solar wind.

The solar wind is a stream of charged particles�a plasma�that are ejected from the upper atmosphere of the sun. It consists mostly of electrons and protons. Now these DO have a mass and will exert a force on the earth equivalent to one of the choices offered. I would imagine it to be well above the weight of a flea, but I don't have enough data to know if it equates to an ocean liner or not.

[Tom Braider]

Light does not have weight but it does exert pressure.
http://en.wikipedia.org/wiki/Radiation_pressur e
I suppose it's just permissible to treat the two things as equivalent but it wasn't really a fair question.

[Rev. Green]

Light does have mass. The confusion arises because photons have no rest mass, however they are never at rest. They move at the speed of light. The mass of a photon is very small: equal to its energy divided by the square of the speed of light. So the blue ones are about twice the mass of the red ones.

[jake-the-peg]

Where the heck did you get that from Reverend?

I think you may have misread something or misunderstood from light having momentum.

Light has no mass

Special relativity tells us that the mass gain of something travelling at the speed of light is infinite


I think you might be thinking of E=mc�

But that's not the full equation.

The full equation relates Energy mass and momentum

E�-(pc�)�=(mc�)� p is momentum

Obviously where there is no momentum you get the well known formula which relates to a body at rest.

In the case of light however there is no mass but there is momentum

so p=E/c� not m=E/c�

[fatgaz]

thankyou all for clearing that up ??????????

[brachiopod]

A Cruise Liner !!!!???

What are they on about? Everyone knows the SMU (Standard Media Unit) of "weight" is the Ddb (Double Decker Bus).

Don't forget the other primary SMU units of "height" - the Nelson's Column, and that of area, the Football Pitch.

[jake-the-peg]

All right I'll put it in words of one syllable

They're wrong you were right

[Rev. Green]

Jake-the-peg is of course correct to say that the full formula for energy includes momentum. However, in the context of the question, it is better to think of light as having mass. (For the purist, I did say that REST mass was zero.) If a source of strong gravitation captures light, the light might circulate, but the consequent increase in gravitational attractive power of the source combined with the light is most readily explained by adding the "mass" (i.e. the energy) of the light to that of the source.
I think the original question meant "Is the solar energy falling on the Earth each day (year?) equivalent to the energy equivalent of a ship, flea, etc.?