Relative Posted October 13, 2014 Posted October 13, 2014 My apologies for so many questions, The Earth spins, and I have heard the spin is slowing down. Is this true?
Janus Posted October 13, 2014 Posted October 13, 2014 Yes, due to tidal interaction with the Moon, the length of Earth's rotational period increases by ~2 milliseconds per century. 1
Robittybob1 Posted October 13, 2014 Posted October 13, 2014 Yes, due to tidal interaction with the Moon, the length of Earth's rotational period increases by ~2 milliseconds per century. That is in accordance with the entry in Wikipedia under Tidal acceleration: From the observed change in the Moon's orbit, the corresponding change in the length of the day can be computed: +2.3 ms/cy (cy is centuries).However, from historical records over the past 2700 years the following average value is found: +1.70 ± 0.05 ms/cy[24][25]
swansont Posted October 13, 2014 Posted October 13, 2014 Yes, due to tidal interaction with the Moon, the length of Earth's rotational period increases by ~2 milliseconds per century. It's an acceleration, slowing by ~2 ms/day/century (Robbitybob1's quote agrees). The current rate of slowing is of order 1 millisecond/day, but it varies over the course of a year. http://tycho.usno.navy.mil/leapsec.html http://maia.usno.navy.mil/whatiseop.html You can see that about a decade ago we had intervals when we were actually speeding up. That's why there were no leap second insertions from 1999 until June 2005 and the smaller average excess length of day is why we've only had a few since then, as opposed to eight in the decade preceding that "dead" interval.
Robittybob1 Posted October 13, 2014 Posted October 13, 2014 It's an acceleration, slowing by ~2 ms/day/century (Robbitybob1's quote agrees). The current rate of slowing is of order 1 millisecond/day, but it varies over the course of a year. http://tycho.usno.navy.mil/leapsec.html http://maia.usno.navy.mil/whatiseop.html You can see that about a decade ago we had intervals when we were actually speeding up. That's why there were no leap second insertions from 1999 until June 2005 and the smaller average excess length of day is why we've only had a few since then, as opposed to eight in the decade preceding that "dead" interval. I was finding that when one thinks of a period "slowing" a little confusing and I'd rather say lengthens or shortens. Do you see my point?
Relative Posted October 13, 2014 Author Posted October 13, 2014 Thank you for confirming the information is correct that I have read. What is the Physical process that makes the Earth spin?
studiot Posted October 13, 2014 Posted October 13, 2014 I posted some information about a similar question in post#9 here http://www.scienceforums.net/topic/86022-lunar-energy/ and I thank swansont for the extra data I asked for there.
Relative Posted October 13, 2014 Author Posted October 13, 2014 I posted some information about a similar question in post#9 here http://www.scienceforums.net/topic/86022-lunar-energy/ and I thank swansont for the extra data I asked for there. Thank you for the lunar energy link, but my question was what makes the spin, I am not at the energy stage yet,
studiot Posted October 13, 2014 Posted October 13, 2014 (edited) The Earth spins, and I have heard the spin is slowing down. Is this true? Did you not bother to read the link? but my question was what makes the spin You need to complete your SF course in torque and moment before this second question can be answered Edited October 13, 2014 by studiot
Strange Posted October 13, 2014 Posted October 13, 2014 Thank you for confirming the information is correct that I have read. What is the Physical process that makes the Earth spin? The solar system was formed from a cloud of gas and dust that collapsed under its own gravity. As this cloud was not stationary, it ended up rotating as it collapsed. The rotation was transferred to the Sun and planets as they formed (because of conservation of angular momentum).
Relative Posted October 13, 2014 Author Posted October 13, 2014 (edited) Did you not bother to read the link? You need to complete your SF course in torque and moment before this second question can be answered I partly read the link , I will refer back to the link when I know some basics first about the moon, I am trying not to run before I can walk... The solar system was formed from a cloud of gas and dust that collapsed under its own gravity. As this cloud was not stationary, it ended up rotating as it collapsed. The rotation was transferred to the Sun and planets as they formed (because of conservation of angular momentum). Ok I thought that would be the answer, and initial inertia was the big bang. Newtons first law is not been broken then by it been slowed down? Edited October 13, 2014 by Relative 1
studiot Posted October 13, 2014 Posted October 13, 2014 I am trying not to run before I can walk... That is really good. +1 The link contains an answer to your first question, not your second one.
Relative Posted October 13, 2014 Author Posted October 13, 2014 That is really good. +1 The link contains an answer to your first question, not your second one. Thank you
Strange Posted October 13, 2014 Posted October 13, 2014 Newtons first law is not been broken then by it been slowed down? I don't think Newton's first law is relevant here as we are talking about rotation rather then motion in a straight line. Speed of rotation can be changed without applying a force. You might have seen ice skaters change the speed of their spin by extending their arms or tucking them in. This is due to conservation of angular momentum.
Relative Posted October 13, 2014 Author Posted October 13, 2014 I don't think Newton's first law is relevant here as we are talking about rotation rather then motion in a straight line. Speed of rotation can be changed without applying a force. You might have seen ice skaters change the speed of their spin by extending their arms or tucking them in. This is due to conservation of angular momentum. I understand speed of a spin can be altered by aerodynamics on Earth in an atmosphere, but Newtons law states that an object in space that has momentum, whether it be linear or rotational should not slow unless an external acting force opposes it. Ok , so what external force acts on the moon?
Strange Posted October 13, 2014 Posted October 13, 2014 Newtons law states that an object in space that has momentum, whether it be linear or rotational should not slow unless an external acting force opposes it. No it doesn't.
Relative Posted October 13, 2014 Author Posted October 13, 2014 No it doesn't. Hmm. yes it does , ''An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.'' a spin is motion.
StringJunky Posted October 13, 2014 Posted October 13, 2014 Relative, on 13 Oct 2014 - 12:11 PM, said: Hmm. yes it does , ''An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.'' a spin is motion. Variations in Earth's rotation (defined in terms of length of day) arise from external tidal torques, or from an exchange of angular momentum between the solid Earth and its fluid components1. On short timescales (annual or shorter) the non-tidal component is dominated by the atmosphere, with small contributions from the ocean and hydrological system. On decadal timescales, the dominant contribution is from angular momentum exchange between the solid mantle and fluid outer core. Intradecadal periods have been less clear and have been characterized by signals with a wide range of periods and varying amplitudes, including a peak at about 6 years (refs 2, 3, 4). Here, by working in the time domain rather than the frequency domain, we show a clear partition of the non-atmospheric component into only three components: a decadally varying trend, a 5.9-year period oscillation, and jumps at times contemporaneous with geomagnetic jerks. The nature of the jumps in length of day leads to a fundamental change in what class of phenomena may give rise to the jerks, and provides a strong constraint on electrical conductivity of the lower mantle, which can in turn constrain its structure and composition. http://www.nature.com/nature/journal/v499/n7457/full/nature12282.html
Relative Posted October 13, 2014 Author Posted October 13, 2014 Relative, on 13 Oct 2014 - 12:11 PM, said: Hmm. yes it does , ''An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.'' a spin is motion. Variations in Earth's rotation (defined in terms of length of day) arise from external tidal torques, or from an exchange of angular momentum between the solid Earth and its fluid components1. On short timescales (annual or shorter) the non-tidal component is dominated by the atmosphere, with small contributions from the ocean and hydrological system. On decadal timescales, the dominant contribution is from angular momentum exchange between the solid mantle and fluid outer core. Intradecadal periods have been less clear and have been characterized by signals with a wide range of periods and varying amplitudes, including a peak at about 6 years (refs 2, 3, 4). Here, by working in the time domain rather than the frequency domain, we show a clear partition of the non-atmospheric component into only three components: a decadally varying trend, a 5.9-year period oscillation, and jumps at times contemporaneous with geomagnetic jerks. The nature of the jumps in length of day leads to a fundamental change in what class of phenomena may give rise to the jerks, and provides a strong constraint on electrical conductivity of the lower mantle, which can in turn constrain its structure and composition. http://www.nature.com/nature/journal/v499/n7457/full/nature12282.html Ok, thank you, so you are saying the Earth and the Moon are a couple and there is a torque involved? Are you saying that forces with no linkage and based on a connection of forces, that there is an energy linkage that creates torque?
Strange Posted October 13, 2014 Posted October 13, 2014 Hmm. yes it does , ''An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.'' Where are you quoting that from? It is over-simplified.
StringJunky Posted October 13, 2014 Posted October 13, 2014 Relative, on 13 Oct 2014 - 12:24 PM, said: Ok, thank you, so you are saying the Earth and the Moon are a couple and there is a torque involved? Are you saying that forces with no linkage and based on a connection of forces, that there is an energy linkage that creates torque? No, that reference was in relation to your question about the necessity for external forces changing the Earth's rate of rotation ...which it isn't. The changes can be caused internally.
Relative Posted October 13, 2014 Author Posted October 13, 2014 No, that reference was in relation to your question about the necessity for external forces changing the Earth's rate of rotation ...which it isn't. The changes can be caused internally. Are you saying it is the electrostatics involved and the repulsion forces of electrostatics?
Klaynos Posted October 13, 2014 Posted October 13, 2014 The ice skater example has nothing to do with there being an atmosphere.
swansont Posted October 13, 2014 Posted October 13, 2014 Are you saying it is the electrostatics involved and the repulsion forces of electrostatics? Nobody has come close to even hinting at that. Mass distribution changes - snowfall in the north melts and the water moves to the equator - will change the rotation rate. Weather systems trade angular momentum with the rest of the earth. Droughts. Lots of different effects. I was finding that when one thinks of a period "slowing" a little confusing and I'd rather say lengthens or shortens. Do you see my point? Yes. The fact that the rotation rate is slower doesn't require an acceleration; the rotation could be constant, and a time difference would accrue - the day gets longer. What is the Physical process that makes the Earth spin? It was born that way. It was never not spinning.
Relative Posted October 13, 2014 Author Posted October 13, 2014 Nobody has come close to even hinting at that. Mass distribution changes - snowfall in the north melts and the water moves to the equator - will change the rotation rate. Weather systems trade angular momentum with the rest of the earth. Droughts. Lots of different effects. Yes. The fact that the rotation rate is slower doesn't require an acceleration; the rotation could be constant, and a time difference would accrue - the day gets longer. It was born that way. It was never not spinning. Thank you I think I understand, you are are saying the rotation slows down by internal means, meaning mass shift, Is electro- motive force ever considered when considering the rotation?
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