Is the earth spinning down theoretically?

[kenny1999]

Everything spinning will spin down if there is friction and no external power injecting to it, right?

How about the earth? Is it theoretically spinning down? (Even if it may take a very long time) But there should not be any friction in the space right because there is no air, is it true?

[exchemist]

1 hour ago, kenny1999 said:

Everything spinning will spin down if there is friction and no external power injecting to it, right?

How about the earth? Is it theoretically spinning down? (Even if it may take a very long time) But there should not be any friction in the space right because there is no air, is it true?

But there is friction in the oceans, in the tidal currents. This is spinning the earth down.

However, angular momentum is a conserved quantity, so if one part of a system spins down due to friction, something else has to gain the angular momentum lost. In this case it is the moon, which is moving to a higher orbit - getting farther away - as a result.

 

[Janus]

Even interplanetary space isn't completely empty.  So technically, there would be some small amount of friction. But things aren't that simple. There are all kinds of things that effect the Earth's rotation.  Tidal interaction with the Moon is a major one. This transfers angular momentum from the Earth to the Moon's orbit, slowing the Earth's rotation over time (on average*)  If were to remove the Moon from the equation, Tidal interaction with the Sun would slowly decrease the Earth's rotation until it locked to the Sun keeping one face to it at all times( unless, due to some effect, it settled into some other orbital-rotation resonance like Mercury has).  But even that wouldn't stop the rotation rate from changing.  The Sun is losing mass as it ages, so the Earth would move to a higher, slower orbit in response, with the rotation slowing to keep pace...   When all is said and done, it is a complicated dance.

 

 

* other things like major shifts/earthquakes can cause the Earth to speed up its spin.  If it causes a net shift inward of the Earth's mass, it is akin to an ice skater bringing in her arms (Only to a much, much smaller degree). Collisions with medium to large meteorites can add or take away spin

[kenny1999]

21 hours ago, Janus said:

Even interplanetary space isn't completely empty.  So technically, there would be some small amount of friction. But things aren't that simple. There are all kinds of things that effect the Earth's rotation.  Tidal interaction with the Moon is a major one. This transfers angular momentum from the Earth to the Moon's orbit, slowing the Earth's rotation over time (on average*)  If were to remove the Moon from the equation, Tidal interaction with the Sun would slowly decrease the Earth's rotation until it locked to the Sun keeping one face to it at all times( unless, due to some effect, it settled into some other orbital-rotation resonance like Mercury has).  But even that wouldn't stop the rotation rate from changing.  The Sun is losing mass as it ages, so the Earth would move to a higher, slower orbit in response, with the rotation slowing to keep pace...   When all is said and done, it is a complicated dance.

 

 

* other things like major shifts/earthquakes can cause the Earth to speed up its spin.  If it causes a net shift inward of the Earth's mass, it is akin to an ice skater bringing in her arms (Only to a much, much smaller degree). Collisions with medium to large meteorites can add or take away spin

Approximately how long will it take for the earth to spin down to an extent that is going to affect human's life? Is there any estimation?

[mistermack]

8 minutes ago, kenny1999 said:

Approximately how long will it take for the earth to spin down to an extent that is going to affect human's life? Is there any estimation?

I can't give an estimated figure, but I think it would take much longer than the human species remains recognizable to us. Our species is about 200,000 years old. In another 200,000 years, the spin will have hardly changed. 

Unless we get hit by something big, that is.

[kenny1999]

1 minute ago, mistermack said:

I can't give an estimated figure, but I think it would take much longer than the human species remains recognizable to us. Our species is about 200,000 years old. In another 200,000 years, the spin will have hardly changed. 

How about the Sun? When will it burn to the end?

[mistermack]

Just now, kenny1999 said:

How about the Sun? When will it burn to the end?

About 5,000,000,000 years from now, although it will get uncomfortable a bit sooner than that. 

[Janus]

19 hours ago, kenny1999 said:

Approximately how long will it take for the earth to spin down to an extent that is going to affect human's life? Is there any estimation?

Due to the Moon's tidal effect, the Earth's period of rotation increases by about 1 sec every 50,000 yrs. (in 50,000 yrs, it will take the Earth one second longer to complete a rotation.) 

As to affecting human's lives, It already does, to a certain extent.   We have reached a point where accurate time measurement has become vital to a great number of fields.   Because of that, the need for a standardized unit of time became very important. This is the second.  For a long time, the second was based on the Earth's rotation. That is, until it became apparent that this wasn't a constant.  The second was switched to be based on something known to be constant, and fixed on that value. The Earth's rotation still changed over time.  

Sure, it was only by microseconds a day per year.  But the effect was accumulative.  For example, imagine a clock that runs slow by one second per day. after 1 day, it will be late by 1 second, after two days 2 sec,... after 60 days, its behind by a full minute, etc.

The same thing happens with the Earth,  from the time we set the length of the sec to a fixed value and now, our Clocks(based on that sec) and the rotation of the Earth vary slightly  Just a tiny bit each day, but it adds up over time.  So, in order to keep them our clocks from drifting too much from the position of the Sun in the sky, every so often a "leap second" is added to our time keeping systems, to line them back up again. (kind of like resetting that clock that runs slow from time to time).

[Doctor Derp]

I would be curious to know if the earth's magnetic field provides shielding against friction from solar wind and other assorted emissions from the sun.

Tidal forces from the moon only exert influence upon the earth's largest oceans. Lakes are too small to be affected by the moon's gravity.

[studiot]

2 hours ago, Doctor Derp said:

I would be curious to know if the earth's magnetic field provides shielding against friction from solar wind and other assorted emissions from the sun.

Tidal forces from the moon only exert influence upon the earth's largest oceans. Lakes are too small to be affected by the moon's gravity.

Deflection of cosmic particles must result in momentum exchange. The net result of that must depend upon the geometry of the deflection.

Tidal forces affect both the liquid and the solid parts of the Earth.
The solid parts may not be free to move as far as the liquid parts (they do move a bit) but they are free to strain and that takes energytransfers.

[Sensei]

"Everything is spinning down".. what an inappropriate/non-scientific choice of words.. Everything goes from a higher energy level to a lower energy level. Decay energy is used to create new particles of various kinds depending on available energy in CoM FoR. The most common particle is the photon (layman version "light").

Spinning object has more energy than non-spinning object. e.g. spinning flywheel vs stationary flywheel.

Friction (interaction of e.g. spinning object with something else, which might be even a cosmic ray in vacuum) decelerates the one which has more energy and accelerates the one which has less energy prior interaction.

[swansont]

11 minutes ago, Sensei said:

"Everything is spinning down".. what an inappropriate/non-scientific choice of words..

I don't think that scolding a layperson for phrasing something in non-technical language is a good look. There's nothing "inappropriate" about that phrasing. You're blaming them for not having learned something yet, and they're here asking questions! 

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Everything goes from a higher energy level to a lower energy level.

One might be tempted to point out to you that this is not generally true; what is true is that going to a higher energy level does not happen spontaneously, and that the post you're responding to said nothing about decay

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Friction (interaction of e.g. spinning object with something else, which might be even a cosmic ray in vacuum) decelerates the one which has more energy and accelerates the one which has less energy prior interaction.

It's entirely possible that any individual cosmic ray could strike the earth is such a way that it would speed the earth up. This is true of any collision, which is why you always have some atoms/molecules with high speeds in a thermal distribution. And why you can do a slingshot with a satellite that speeds it up, even though it has far less energy than the planet.