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B Does earth mass get heavier?

  1. Nov 19, 2016 #1
    Trees, plants grow. people eat, animals eat. Their dungs in ground everyday. People die. Does it have effect on the earth mass? On its orbit around the sun?
     
  2. jcsd
  3. Nov 19, 2016 #2

    Doc Al

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    Why would you think any of that affects the mass of the earth?
     
  4. Nov 19, 2016 #3

    mfb

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    Does your food come from space?
     
  5. Nov 19, 2016 #4
    Now wait, mass can be converted to energy and it doesn't require a nuclear reaction. Every chemical reaction changes the mass of the constituents by the change in the binding energy.

    However there are two reasons why this is negligible. First. The earth is in somewhat of a steady state. The chemical configuration today is not much different than yesterday. Second, and much much more importantly, the effect is minuscule. Even if you set fire to the earth and burned every bit of the surface to its lowest energy state I don't think you would change the mass significantly. Completely irrelevant, but fun to contemplate.

    I believe the most significant contribution to changing the earths mass is the accretion of bits and pieces from space. Much much much more relevant than the previous ... and yet still pretty negligible. Estimates vary, but it could be 60 tons per day. That sounds like a lot, but it's 20 orders of magnitude less than the mass of the earth. In a billion years it would still only change the mass by one part in 10^8. Completely irrelevant.

    Then there's the mass of our deep space probes. Now THAT is eroding the earth at an alarming rate!
     
  6. Nov 19, 2016 #5

    mfb

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    ~150 missions to leave Earth orbit in 55 years, for a rate of a few tons per year. Add something like 10,000 tons in Earth orbit, then we have 200 tons per year, but most of that mass will fall back to Earth eventually.

    The mass-energy equivalent of geothermal heat is about 10-15 tons per year.
     
  7. Nov 19, 2016 #6

    Nugatory

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    Imagine a large spherical surface surrounding the earth. Everything (energy, space probes, gas molecules escaping the atmosphere, ....) passing outwards through that surface reduces the mass of the earth. Everything passing in through it (energy, meteors, cosmic radiation, stray space dust, ....) increases the mass of the earth. Everything that happens inside the sphere and stays inside it (growing plants, consuming food and defecating, water falling from the sky as rain and evaporating back into clouds, ....) has no effect on the mass.

    In practice, all of these effects are so small that we can take the mass of the earth to be constant without introducing significant erros into our calculations.
     
  8. Nov 19, 2016 #7

    Your answer: convert mass to energy may be the solution to my question.
     
  9. Nov 19, 2016 #8
    Cutter Ketch's reply: mass convert to energy may be the answer. Your answer is good, but I am not happy. We are aware that we defecating everyday. It should add up. Animals,too. They are doing that since dinosaurs' days.65 million years ago. It should add up by now..significantly. People die every day.. it should be lots more dead in the ground than live ones like you and me. The probability has to be 1000 to 1. Common sense will agree with me. Don't count zombies. I think mass convert to energy is the answer. We cannot weigh energy so small.
     
  10. Nov 19, 2016 #9

    Janus

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    In addition to what others have already touched on, we have to consider the second half of your question, what effect would this have on Earth's orbit. The fact is that since the Sun's mass is so much greater than the Earth's, it dominates the nature of the orbit. For example, even if we assumed that the mass of the Earth suddenly doubled, and all else(orbital speed etc.) stayed the same, the effect on the Earth's orbit would be smaller than than its present variation due to the eccentricity of its orbit.
     
  11. Nov 19, 2016 #10
    Doesn't the solar energy collected by photosynthetic plants then incorporated into organic molecules add a little to the mass of Earth?
     
  12. Nov 19, 2016 #11
    Good question. I always buy food at Shoprite. Workers may be spacemen.
     
  13. Nov 19, 2016 #12
    Thank you for the thought.
     
  14. Nov 19, 2016 #13

    Janus

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    What we defecate is the waste left over from what we eat. What we eat comes from the mass of the Earth. In other words, what we defecate does not add to the mass of the Earth as it was always a part of the mass of the Earth. The same with the dead, everything that made up their bodies was always there as a part of the Earth's mass.

    Besides, I don't think you realize just how small the total mass of living and dead animals (including humans) is compared to the mass of the Earth as a whole, We are talking about a fraction that is less than 1/1,000,000,000.
     
  15. Nov 19, 2016 #14

    DaveC426913

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    Shouldn't we be tackling the OP's confusion from a slightly more systemic vantage point?

    Sources of mass/energy input:

    • solar radiation (EMR), solar wind (particles)
    • infalling comets, meteors, stray dust, gas
    Sources of mass/energy output:
    • heat loss (EM radiation)
    • escaping atmosphere (particles)
    Everything else:
    • all people,
    • all animals,
    • all plants, fungi and bacteria,
    • their breaths, their food, their defecation,
    • their reproduction, their births, their deaths
    are all mass neutral - they take from what is there, move it around a lot then deposit pretty much back where it came from - on Earth.
     
  16. Nov 19, 2016 #15
    Good thought. Maybe someone can help you about the energy cuz it's has no gravitational tendency like mass. Looks like to me that energy is just electrostatic, repelling and attracting each other in all directions although intact inside that it counterbalances virtually zero resulting miniscule in weight. Hidden.
     
  17. Nov 19, 2016 #16

    DaveC426913

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    No, it is not hidden.
    Energy's mass can be derived from E=mc2
     
  18. Nov 19, 2016 #17

    jbriggs444

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    Yes, Simba, but let me explain. When we die, our bodies become the grass, and the antelope eat the grass. And so we are all connected in the great Circle of Life.
     
  19. Nov 19, 2016 #18
    Hey, that brings up an interesting point. That doesn't conserve momentum. Forget the earth. Say a nuclear bomb is in orbit around the sun. When the bomb explodes suddenly a significant fraction of the mass disappears. Say the explosion is spherically symmetric so the center of mass doesn't change. How is momentum conserved? It has to be, so where would it go?
     
  20. Nov 19, 2016 #19

    DaveC426913

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    This is a different question, and warrants its own thread so as not to derail this one.

    But here's a teaser:
    What makes you think it simply disappears? We're talking mass/energy conversion here, not disappearance.
     
  21. Nov 19, 2016 #20
    Yes, I shouldn't have said it like that. In fact I added "is it in the momentum of the generated photons?" But erased that to avoid steering the answers. However, I really don't see in detail how the conservation comes about. Maybe I will start a new thread. Interested parties can look for it.
     
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