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sleepsleep



Joined: 05 Oct 2006
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sleepsleep
ok,
i don't quite understand this,

since, the sun shine and release lots of energy on earth,
then things grow, flourished, and sun keeps on shine,

does this make the earth increases its mass from time to time?
and since, earth only keeps on receiving, be it sun light, asteroid impact, or etc,
our output only some satellites,

since energy cannot be created or destroyed,
so, more energy on earth from time to time?

am i correct?
Post 19 May 2014, 16:28
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revolution
When all else fails, read the source


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revolution
The light energy is not converted to mass. It is either reflected or re-radiated back into space. The biomass of plants comes from the existing matter already here.
Post 19 May 2014, 23:02
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revolution
When all else fails, read the source


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revolution
Oh, I forgot to add that meteorite impacts do increase the mass of the Earth.
Post 19 May 2014, 23:29
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sleepsleep



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sleepsleep
thanks for the information, revolution,
am i wondering why light energy doesn't increase earth's mass,

does those photons actually travel from sun to earth surface? cause i saw light hits everywhere on earth.
Post 19 May 2014, 23:58
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gens



Joined: 18 Feb 2013
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gens
because it is radiated away
random atoms also leave the earth

brownian motion is how

about light, i found a nice talk that might interest you
http://www.youtube.com/watch?v=IyUgHPs86XM
Post 20 May 2014, 00:38
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revolution
When all else fails, read the source


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revolution
Post 20 May 2014, 01:51
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Xorpd!



Joined: 21 Dec 2006
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Xorpd!
The sun's light most definitely increases the earth's mass when a photon of light is absorbed as heat or causes chemical change via photosynthesis. Ordinarily one only talks about interconversion between mass and energy when the photon energy is in the gamma ray range (about an MeV rather than about an eV for visible light) because then the differences in nuclear mass are detectable by high-resolution mass spectroscopy in that case, but a small change in mass no doubt happens for chemical change as well.
Solar neutrinos can increase the earth's mass by causing nuclear changes or via elastic scattering. That's how we attempt to detect solar neutrinos.
Sunlight probably is responsible for more loss of mass than gain, however, because any planetary atmosphere is unstable in a thermodynamic sense and sunlight, at least indirectly, causes atoms and molecules in the upper atmosphere to be launched into ejective orbits.
Post 26 May 2014, 22:32
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typedef



Joined: 25 Jul 2010
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typedef
revolution wrote:
Oh, I forgot to add that meteorite impacts do increase the mass of the Earth.


You mean having the meteorite on Earth or just that one time it hits it.

Anyway, I'm sure the dust that goes into the atmosphere and precipitation work against that. Of course a lake or river can't just evaporate within a single day. But still, nature has its own way of balance.

Maybe when there's huge droughts mother nature is trying to shave off some weight; like on a diet.
Post 27 May 2014, 04:59
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revolution
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revolution
The weight of the Earth includes the atmosphere. The atmosphere does leak into space as mentioned above but overall the meteorite impacts more than balance the atmospheric losses for an overall gain. The gain is minor though IIRC something like 100 tonnes per annum on average or thereabouts. I'm to lazy to check that figure right now perhaps someone can find a source that disprove my memory?

As for photons increasing the mass of an atom when it places the electron into a higher orbit ... I am very sceptical about Xorpd!'s claim there.
Post 27 May 2014, 05:25
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l_inc



Joined: 23 Oct 2009
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l_inc
revolution wrote:
I am very sceptical about Xorpd!'s claim there

Me too. The energy gained by plants is converted into chemical bond energy (enthalpy), which is at a lower perspective a mutual potential energy of atoms. It is by no means mass (to my knowledge). The only way of mass-energy conversion I knew before this topic were nuclear reactions, and that is how the sun loses the mass by converting it into the released photons.

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Post 27 May 2014, 13:53
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edfed



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edfed
mass doesn't change with light, but weight can due to temperature changes.

but as the matter on earth is always on earth, even if local objects loss weight, the global weight might not change.
Post 27 May 2014, 15:05
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revolution
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revolution
edfed wrote:
...but weight can [change] due to temperature changes.
I am sceptical here also. Confused
Post 27 May 2014, 15:11
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edfed



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edfed
relative weight Smile

weigth is just a relative feeling of a mass, mass is constant and don't depend on the gravity, but weight depends on gravity, temperature, presure, etc...
Post 27 May 2014, 15:43
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Xorpd!



Joined: 21 Dec 2006
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Xorpd!
revolution wrote:
As for photons increasing the mass of an atom when it places the electron into a higher orbit ... I am very sceptical about Xorpd!'s claim there.

The loss in mass when a gamma ray is emitted from a metastable nucleus such as Tc-99m is well within the detectability limits of high-resolution mass spectroscopy.
Why should it be expected that gains or losses in mass due to absorption or emission of photons that are below available detection thresholds are other than what you would get from simple application of E = hf = mc²?
Also the rate of atmospheric mass loss may be higher than you anticipate. Consider how much more atmosphere Venus has than us, and that gases are replenished by volcanic activity. Certainly there would be much more He in the atmosphere than there actually is because radioactive decay produces it much faster than Ar-40 is produced by decay of K-40, unless most of it has been lost to space. In fact the atmosphere is about 1% molar Ar-40 but only a few ppm He-4.
Post 27 May 2014, 22:28
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l_inc



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l_inc
Xorpd!
Quote:
Why should it be expected that gains or losses in mass due to absorption or emission of photons that are below available detection thresholds are other than what you would get from simple application of E = hf = mc²

For the same reason as you would expect no changes in mass when lifting an object from the ground. There is just an increase in the (potential) energy. The equation does not say that mass is energy. It describes how much energy corresponds to an amount of mass in case of complete conversion.

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Post 27 May 2014, 23:49
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Xorpd!



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Xorpd!
l_inc wrote:
Xorpd!
Quote:
Why should it be expected that gains or losses in mass due to absorption or emission of photons that are below available detection thresholds are other than what you would get from simple application of E = hf = mc²

For the same reason as you would expect no changes in mass when lifting an object from the ground. There is just an increase in the (potential) energy. The equation does not say that mass is energy. It describes how much energy corresponds to an amount of mass in case of complete conversion.

I would take too much space here to explain all the ways in which your thinking is wrong, but Einstein wrote a very comprehesible book (as well as several very technical treatises) on relativity, and if you are interested in learning more I suggest you read it.
Maybe it would be constructive to think about the energy-momentum 4-vector relationship: E² = (pc)² + (mc²)² where given the energy E and momentum p of a system we can find its mass m. If we started with an electron-positron pair I think just about anyone would conclude that the system has mass 2m_e, where m_e is the electron mass. Given the observer is in the center of momentum frame so that p = 0 we can calculate the energy as observed in our frame to be 2m_ec².
Simple enough, right? But now what happens when the pair annihilates but not enough time has passed for the photons to have moved far enough away that we would no longer consider them to be contained within our 'system'?
The energy as observed in our frame would still be the same, and the net momentum is still zero, so we would conclude that the energy-momentum 4-vector still had the same magnitude, so the system of two photons has the same mass as the original electron-positron pair. So even though as a rule a single photon can never have mass because E = pc, a system of two or more photons can have p < E/c and so have nonzero mass. Similarly a system consisting of a massive object and a photon need not have the same mass as the massive object alone.
Post 28 May 2014, 09:27
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typedef



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typedef
Post 28 May 2014, 12:19
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Xorpd!



Joined: 21 Dec 2006
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Xorpd!
typedef wrote:
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961102.html

The article doesn't address an important distinction I made in my previous post: a photon has no mass, but a collection of more than one photons does, unless they are all moving in the same direction.
Post 28 May 2014, 13:04
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l_inc



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l_inc
Xorpd!
Quote:
system of two or more photons can have p < E/c and so have nonzero mass

A system of two photons, traveling at speed of light in opposite directions, depending on the observer, etc... This raises lots of questions in my head (like how far should the photons travel in empty space, so that you can't consider them a single system anymore?), because I'm not much on the relativity theory, and therefore won't be able to withstand your argumentation.

But let us look at a simple example with a motionless object absorbing a photon, where the relativistic effects do not matter, because I think your logical transition to a system with a massive object is invalid:
Quote:
Similarly a system consisting of a massive object and a photon need not have the same mass as the massive object alone.

I think, there's no similarity here. Let's forget about more complex processes of converting light into the chemical bond energy in plants and look into the process of excitement of a hydrogen atom (Lyman-alpha transition) as suggested by revolution. Do you think, that the increased potential energy of the electron results in the increase of its mass or the mass of the atom as a whole?

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Post 28 May 2014, 13:10
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Xorpd!



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Xorpd!
l_inc wrote:
I think, there's no similarity here. Let's forget about more complex processes of converting light into the chemical bond energy in plants and look into the process of excitement of a hydrogen atom (Lyman-alpha transition) as suggested by revolution. Do you think, that the increased potential energy of the electron results in the increase of its mass or the mass of the atom as a whole?

The system as a whole gets more mass. Electrostatic potential energy can always be viewed in terms of the energy of the electric field where the energy density is u = ½ε_0E². Add up that electrostatic field energy over all space, divide by c², and that's where the mass comes from.
In nuclear physics, where we should recall that the electrostatic forces play a not insignificant role, it's commonplace that changes in energy imply changes in mass, whether measured by mass spectroscopy or by weighing a ponderable mass consisting mostly of atomic nuclei. Chemical energy is only a difference in degree, not a qualitative difference. If it were not so, fundamental things like the continuity equation for mass wouldn't work.
Post 28 May 2014, 18:02
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