# Earth rotation at equator

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#### ace5

##### Guest
What is the velocity of the Earth´s rotation at equator, in km/sec?<br /><br />Did it change significantly in the past 10.000 yrs?<br /><br />thanks.

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#### MeteorWayne

##### Guest
Well, the diameter is 12,756 km.<br />Therefore the circumference is Pi*d=40074 km.<br />That distance in accomplished in just under 24 hours, so it's about 1670 km/hour or about 464 meters/sec at the equator. I'll let you convert that into km/sec <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### ace5

##### Guest
Thanks,<br /><br />"464 meters/sec at the equator. I'll let you convert that into km/sec "<br /><br />So, it is 0,46 km/sec

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#### MeteorWayne

##### Guest
Yep <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### derekmcd

##### Guest
<i>"Did it change significantly in the past 10.000 yrs? "</i><br /><br />Significant depending on whom you've asked. Has it changed? <br /><br />Yes it has.<br /><br />Tidal forces between the moon and earth and sun create what is referred to as gravitational locking. <br /><br /> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### MeteorWayne

##### Guest
OK, it's slowed by about 2 minutes in 10000 years, so it used to be 23 hr 54 minutes, now it's 23 hr 56 minutes.<br /><br />Is that significant?<br /><br />I guess it depends on what you're using the information for. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### derekmcd

##### Guest
Significant in knowing, simply, that it <i>IS</i> happening and the consequences thereof... <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### MeteorWayne

##### Guest
Well let's see what ace5 thinks.<br />He asked the question <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### newtonian

##### Guest
MeteorWayne - That fast, or - er - slow?<br /><br />That would be quite a bit since earth was created some 4.5 billion years ago!<br /><br />And it would be quite a bit more by the time our sun goes red giant - assuming (which I don't btw) current stellar evolution models are correct for our sun.<br /><br />I thought the change was much slower than that, such that earth will have a 25 hour day in 5 billion years or so.<br /><br />Let's see - 2 minutes in 10,000 years; 20 minutes in 100,000 years, 200 minutes in 1 million years, 200,000 minutes in 1 billion years.<br /><br />Now, 24 hours is 14,400 minutes?<br /><br />So, 1 billion years ago earth's day was how long?<br /><br />I assume that would not be negative time!!!!!!

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#### MeteorWayne

##### Guest
The current rate is about 0.7 sec per year.<br />That rate of change is not constant. It has to do with the transfer of momentum between the earth and the moon. Long ago the day was much shorter.<br />Eventually the day and the moon's orbital period will become the same, if we don't get toasted first. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### derekmcd

##### Guest
I believe the rate of decay of the earth's rotation is far, far less than that. On the order of 1-2 ms per century (I forget the exact number). And this number can be verified exactly via atomic clocks. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### MeteorWayne

##### Guest
Yes, you are correct, the long term rate is much less than what I quoted, I've been investigating different sources. The rate over the last decade or so has been 0.7 sec a year, but that is an exceptional rate of change.<br /><br />Thanx for correcting me. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### derekmcd

##### Guest
<i>"The rate over the last decade or so has been 0.7 sec a year, but that is an exceptional rate of change."</i><br /><br />Could you point me towards that source? As you said... seems rather exceptional. <br /><br />No doubt in my mind the rate of decay fluctuates. Sometimes the decay is enough that following lengthy periods, the earth will regain momentum and speed up. Over the long term, though, it is, in fact, slowing.<br /><br />These fluctuation are, however, measure in milliseconds per century. I would think 7/10ths of a seconds per year would make news. The forces to affect the earth's rotation on that scale would have to be rather large. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### MeteorWayne

##### Guest
I'll look. Fpr the last decade there has been about 1 leap second per year added.<br />I'll try and find the reference I used.<br /><br />Just as a side note, the shift in mass caused by the Sumatra quake in 2004 produced a step-change in the rotation rate. IIRC, it sped up the rotation, though that memory could be faulty <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

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#### derekmcd

##### Guest
The recent slew of leap seconds added over the last 35 years stem from Earth's orbit about the Sun... Not its daily rotation about its axis. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### dragon04

##### Guest
Okay. Maybe an obtuse and naieve question, but given the nature of a molten core and its effect on rotational velocity, will there ever come a time when the Moon's orbit and Earth's rotational velocity aren't directly proportional or maybe I should say less directly proportional? <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

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#### derekmcd

##### Guest
They will always be proportional as the total angular momentum of the 2 body system will remain the same. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### rfoshaug

##### Guest
And one day (a very long time from now) the Earth's rotation and the Moon's orbit will be of the same length so that the same side of Earth always faces the Moon in the same way that the one side of the Moon is always facing Earth.<br /><br />Just like in the Pluto-Charon system. When that happens, there will be no further energy transferring between the two, and they will keep their rotational periods forever if not disturbed by outside forces. <div class="Discussion_UserSignature"> <p><font color="#ff9900">----------------------------------</font></p><p><font color="#ff9900">My minds have many opinions</font></p> </div>

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#### derekmcd

##### Guest
Indeed. It's referred to as gravitational locking which is due to tidal forces between the two. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### ace5

##### Guest
Nevermind!<br /><br />I post this question here because there was a crazy guy in anotther forum claiming that ETs would be rescuing us, poor humans, soon, since the Earth´s rotation (according to him 380 km/s !!!!) is dangerously slowing down...<br /><br />And I asked here for data about the Earth rotation, to put the guy in his deserved place:<br /><br />The limb of the forgotten.<br /><br />thanx!

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#### nexium

##### Guest
I get about 0.4 kilometers per second for the speed of Earth's equator and the speed has slowed only slightly in recent centuries. Dangerously slow is likely about a million years in our future. ET may need to rescue humans from something, but slowed rotation is very low probability. Neil

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#### derekmcd

##### Guest
<i>"You have that exactly backwards. Leap seconds correct for Earth's daily rotation only. Earth's orbit has nothing to do with leap seconds."</i><br /><br />Good call on my mistake. I might have been thinking about leap years when the conversation had nothing to do with it. Not sure how could mix that up, but I did. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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