Is the earth getting heavier or lighter?

[Bakhesh]

Ok, so Earth is getting heavier by up to 100,000 tonnes per year. My follow up question is, does this affect the rotation of the planet?

I seem to remember from high school physics that linear momentum is worked out by multiplying mass and velocity, so as the mass of the planet increases, wouldn't the speed of rotation decrease? (I also remember that rotational dynamics were a lot more complicated than linear dynamics, but the same principals should apply)

[C K Dexter Haven]

Link to Column: http://www.straightdope.com/columns/...ier-or-lighter

[Powers]

Originally Posted by Bakhesh

Ok, so Earth is getting heavier by up to 100,000 tonnes per year. My follow up question is, does this affect the rotation of the planet?

I seem to remember from high school physics that linear momentum is worked out by multiplying mass and velocity, so as the mass of the planet increases, wouldn't the speed of rotation decrease? (I also remember that rotational dynamics were a lot more complicated than linear dynamics, but the same principals should apply)

The Earth's speed of rotation is already decreasing thanks to the tidal effect of the moon. I suspect any further effect from accumulated mass is negligible.


Powers &8^]

[MarvinKitFox]

Slight correction, as in "You are totally off your gourd, next time check your facts"

The Great Cecil's post states "It's believed the earth gains anywhere from several dozen to several hundred tons per day due to meteorites and meteoritic dust — 10,000 to 100,000 tons a year. (Sorry, but estimates vary widely.) This far exceeds any losses"

Try this for losses:
In Hydrogen only: 18 to 40 Kilogram per second.
That is roughly 568 000 tons to 1 260 000 tons per year of mass loss.

This quite handily exceeds any estimate of mass gain from meteoric origins.

There are other losses/gains to look at, but yes they are quite a bit less.
gain: Accretion from solar wind. (about 10% as much as the H2 loss)
loss: Radioactive decay in the core
a) subsequent heat loss through surface: 20TW= about 7 tons per year
b) Energy loss as neutrino's from the decay: about 15 tons per year.
loss: Tidal slowing of earth, generates heat, loss of about 3 tons per year.
loss: Energy from human consumption, lost as heat: about 500 exajoule, a mere 6 tons.
loss: Stuff rocketed into space: considering that almost all rocket fuel burnt at orbital height exceeds escape velocity: several hundred tons per year!

Shall we look for more? I'm sure I missed a few dozen sources

[ZenBeam]

Where did you get the "18 to 40 Kilogram per second" figure? Looking around, I see 3 kg per second, e.g. here and here.

That first link claims that overall the Earth is getting lighter by about 50,000 kg per year, so your overall remains, though.

In Cecil's defense, I'll note the column is from 1989. In this paper from 1969 (PDF), the author writes (Note: you have to select the text to read it. The scan is illegible otherwise):

T h e rate at which h y d r o g e n is supplied t o the Earth
by the solar w i n d , and the rate at which h y d r o g e n escapes f r o m the E a r t h
by diffusion into space are compared 011 the basis of recent estimates.
It is f o u n d that the hydrogen supplied by the solar w i n d is roughly compar-
able to or m a y even be larger than present h y d r o g e n losses.

Hard to say what the scientific opinion was when the column was written.

[cynyc]

I don't know if the mass of the earth is increasing in a significant degree, unless mass also applies to weight.

Now the weight of the earth is changing because we have billions of people who won't stop procreating, adding even more weight, and then those obese American kids. At best the droughts and subsequent lack of food, particularly McDonalds, or beef if you will, will make the fat kids skinny, unless, of course, the gov hands out tons of processed cheese food.

I don't know about the earth's rotation. Had it been impacted when the Great Meteor hit?

Support Planned Parenthood.

[Powers]

I'm not sure you have any idea what you're talking about.


Powers &8^]

[gamerunknown]

It's simple, we can avoid this fragile globe collapsing if we cure obesity with abortions.

[Bozuit]

Surely the Earth must be lighter by now. We keep dumping all our metal on Mars.

[gnoitall]

Originally Posted by Bozuit

Surely the Earth must be lighter by now. We keep dumping all our metal on Mars.

Mars manages to land some of its rock on Earth from time to time, too. Hard to know if this is a continuing process or just geological-historical.

My calculations from that page show that we know of about 91 kg of Mars rock on Earth. Of course, we totally tipped that balance into an Earth weight deficit when Viking 1 landed, since its lander masses 572 kg by itself. (Assuming there's not some mountain-sized Martian-stone meteorite buried someplace we haven't looked.)

[Irishman]

Originally Posted by cynyc

Now the weight of the earth is changing because we have billions of people who won't stop procreating, adding even more weight, and then those obese American kids. At best the droughts and subsequent lack of food, particularly McDonalds, or beef if you will, will make the fat kids skinny, unless, of course, the gov hands out tons of processed cheese food.

This is complete gibberish. Increase in human population, and feeding people to be fat instead of skinny, only redistributes the existing mass from one location and form to another. It does not increase the mass of the planet.

Weight in this context is just a stand in for mass. Fat people weigh more, because they have more mass in one location for gravity to act on all at once. The gravity field is determined by the amount of matter collected together. Weight is a function of the distribution of that matter. Move matter from pile of dirt over here to belly over there through the process of growing plant matter, or perhaps feeding said plant matter to animal and then processing animal into food source.

[ukdave]

The weight of an object is merely the measurement of the effect gravity has on that object. In space the same object would have no weight.

Since gravity is a force generated by the mass of the earth, the weight of the earth cannot be measured in this way.The earth cannot "weigh" itself!

The earth is an object in space and therefore is weightless.

The answer to the question is "no".

[Irishman]

Answer to which question?

[HippieMagic]

I'm still confused how more people aren't more weight.
I mean I get how everyone comes from what's already here, our sperm and eggs.. And that babies only grow up and get bigger from what they eat which is already here...
But don't all our bones, organs, and even our bag of skin weigh more than sperm and eggs? I guess I just don't know where it all comes from =)

~Appreciate feedback

[HippieMagic]

@ukdave
Okay, so the Earth can't actually weigh anything since we only judge our weight based on our gravitational pull to the Earth itself in the first place.
But if the Earth is gaining mass, then gravity should be getting stronger right?

[John W. Kennedy]

Originally Posted by HippieMagic

@ukdave
Okay, so the Earth can't actually weigh anything since we only judge our weight based on our gravitational pull to the Earth itself in the first place.
But if the Earth is gaining mass, then gravity should be getting stronger right?

Yes, though it's partly canceled out by the surface of the Earth getting further from the center. But both effects are much too small to measure.

[ZenBeam]

Originally Posted by HippieMagic

I'm still confused how more people aren't more weight.
I mean I get how everyone comes from what's already here, our sperm and eggs.. And that babies only grow up and get bigger from what they eat which is already here...
But don't all our bones, organs, and even our bag of skin weigh more than sperm and eggs? I guess I just don't know where it all comes from =)

~Appreciate feedback

It all comes from food. How much food have you eaten over your lifetime? Tens of tons of it, at a guess. The real mystery is, why do you weigh so little?

[HippieMagic]

Poop Zen. . poop.

[HippieMagic]

Thanks for the explanations guys ^__^

[For You]

Originally Posted by MarvinKitFox

Slight correction, as in "You are totally off your gourd, next time check your facts"

Your figures pertaining to heat are absurd. The earth's total energy budget is around 174PW from the sun alone, which pretty much dwarfs all the other heat sources combined. I am not clear on whether the energy budget is actually in balance, but the numbers you put forth for heat (mass) loss have not been adjusted for incoming solar radiation, which is a lot – even the solar variation is greater than all the other heat. The earth does not seem to be getting significantly colder, it appears to be very close to a balanced energy budget, so the mass loss you ascribe to heat radiation strikes me as highly unlikely.

Then there is all the junk we have shot into space: how much of it leaves the earth? Booster stages fall back and burn up, returning to earth. Many other parts float around for a while, maybe even staying in orbit for a very long time. And tens of thousands of satellites remain in earth orbit for years or longer. Really, just because a thing is not on the ground does not mean it is no longer part of the planet, anything that is in the gravity well is not net "lost mass".

So before you go cussing out Cecil, consider that the situation might not be as simple as you think.

[Irishman]

Originally Posted by HippieMagic

I'm still confused how more people aren't more weight.
I mean I get how everyone comes from what's already here, our sperm and eggs.. And that babies only grow up and get bigger from what they eat which is already here...
But don't all our bones, organs, and even our bag of skin weigh more than sperm and eggs? I guess I just don't know where it all comes from =)

Sure, adults weigh more than (and are larger than) eggs and sperm. Where does that growth come from? Answer - food. Where does the food come from? Animals and plants. Where to animals get it? Plants. So it boils down to plants.

Where do plants get the matter that eventually gets turned into people? They get carbon from the air, water from the environment, some nitrogen and such from the soil.

So, whether it is people, or cows, or trees, or grass, or corn, all living matter grows by taking mass that is already on the planet Earth and recombining it into a new arrangement. More people, fatter people, etc are all still just rearranging the mass that the Earth already has. The only way that changes is when the aliens show up and start migrating here.

[ukdave]

Originally Posted by Irishman

Answer to which question?

Short term memory loss!

The question was "Is the earth getting heavier or lighter? " (See OP)

[ukdave]

I know it's difficult, but try to see it this way.

There is no such thing as weight; there is only gravity.

If things had weight, everything would fall to the bottom of space!

[ZenBeam]

A smart-ass answer to a question asked colloquially. Color me unimpressed. You old enough to drive yet?

You could try answering the interesting question: Is the Earth getting more or less massive?

[Quercus]

Originally Posted by Bakhesh

Ok, so Earth is getting heavier by up to 100,000 tonnes per year. My follow up question is, does this affect the rotation of the planet?

I seem to remember from high school physics that linear momentum is worked out by multiplying mass and velocity, so as the mass of the planet increases, wouldn't the speed of rotation decrease? (I also remember that rotational dynamics were a lot more complicated than linear dynamics, but the same principals should apply)

Anyway, for the sake of the question, assuming there is a net mass gain, then, yes this would slow the rotation. But of course by an immeasurably tiny amount, as the gain is immeasurably tiny compared to the amount of mass already rotatiing.

And this assumes that angular momentum around the Earth's axis of the incoming mass sums out to zero. There may well be something about the Solar System that means this isn't true, so you'd have to account for this as well. Though again, 'immeasurably tiny' is the applicable description.