[Geof]

Dear Geof,

Your thread threw up the idea of exporting "dead stuff" to space as an alternative to cremation..... Best wishes,

Martin

No, no, no; go back and read again. The suggestion was to obtain energy with some harebrained space based scheme and use the energy to convert dead people and old trees to an oily pulp.

[martinw]

No, no, no; go back and read again. The suggestion was to obtain energy with some harebrained space based scheme and use the energy to convert dead people and old trees to an oily pulp.

Dear Geof,

Hush...

ORD(Orbit Re-alignment Denial) is now a criminal offence.

Best wishes,

Martin

[fizzissist]

The earth wobbles in it's orbit as it is...in fact, the big earthquake that caused the Xmas tsunami of '04 actually shifted the earths CG and changed its wobble by a few centimeters.

If you increase the mass, you'd need to do it uniformly, or you'll worsen the wobble...not necessarily a good thing! The existing wobble affects climate cycle (I'm not sure offhand what the period(s) are).

The other down side to increasing the mass is increasing gravitational attraction, which will pull the moon closer, and pull us, as a system, closer to the sun.

Much more serious as a side effect will be the shift in astrological forecasts. I'm not sure I'd wanna risk becoming a capricorn!!

Let's not screw with nature any more than we already do. Every time we do, we inevitably make things worse in the long term.

[Geof]

The earth wobbles in it's orbit as it is...in fact, the big earthquake that caused the Xmas tsunami of '04 actually shifted the earths CG and changed its wobble by a few centimeters...

Was it really a few cm??? I thought it was a fraction of a centimeter; certainly measurable but pretty small compared to the earth.

....If you increase the mass, you'd need to do it uniformly, or you'll worsen the wobble...not necessarily a good thing! The existing wobble affects climate cycle (I'm not sure offhand what the period(s) are).....

Isn't that the 25,000 year one in the Milankovitch cycles?

If you bring it in a dust just at a much greater rate than at present it should distribute fairly uniformly. But then I suppose if you filled the atmosphere with dust you don't need to worry about Global Warming anymore .

But what does it do to day length? This stuff coming in does not have the same angular momentum as the Earth so the spin will slow down. I would expect 48hour days might be as difficult, if not more difficult, to adapt to as Global Warming.

As Mr Rabbit Food said we need a bigger grant to study this.

[ImanCarrot]

Aha! this cosmic dust thing has enlightened me to a puzzle that has bugged me for many a year...

We're importing cosmic dust all the time (as a planet) and hence the mass of the earth is getting larger- this explains why all old biblical cities are under the ground!

Also, if the earth is gaining mass then it logicaly should orbit the sun a bit slower (like a bigger mass on the end of a string) and hence years will be longer... this explains why old guys in the bible lived for 200 years and stuff... the years were shorter.

Goodness! Einstein and Hawkins have nothing on us lot *phew*

One question that has been also bugging me for years is: how fast does gravity travel? Like, if you removed the moon how soon would the tides "know", would it be instantaneous or at the speed of light?

Sorry to ramble it's Monday and I've only had two cups of coffee and me machine is on a warmup cycle.

But what does it do to day length? This stuff coming in does not have the same angular momentum as the Earth so the spin will slow down. I would expect 48hour days might be as difficult, if not more difficult, to adapt to as Global Warming.

I suspect this is a cunning ploy by the powers that be to get us working longer hours *peers about in a paranoid fashion*.

I need more funding please to dig for these ancient cities... my excavation equipment is not very high tech (see below).

[sdantonio]

Dear All,

I never got to grips with astronomy, and my knowledge of gravitational pull is mighty thin. I would be very grateful if anybody could enlighten me on these issues...

1) If you increase the mass of the Earth ( say, by importing rubble from far off planets), would the Earth assume an orbit round the Sun that is of a smaller "radius" compared to the present one, or a larger radius? (I'm guessing a smaller radius, but may well be wrong).

2) If there is a natural change in radius, does the Earth have to be moved to it, or will it assume it of its own accord ?

Incidentally, I think that ImanCarrot's posts are two of the funniest pieces I have ever read. I was helpless. Thank-you.

Best wishes

Martin

Hi Martin,

This is the simple answer from Kepler's laws pf planetary motion.

LAW 1: The orbit of a planet about the Sun is an ellipse with the Sun's center of mass at one focus. This means part of the time the earth is closer than at other times.

LAW 2: A line joining a planet and the Sun sweeps out equal areas in equal intervals of time. When the Earth moves in closer to the sun, it's orbital speed inccreases. Think of it this way. In any minute the Earth sweeps out a pie shaped arc in space. Those pie shaped arcs are always the same size in square inches (nobody gets jipped on their piece of pie). They can be long and skinny of short and fat, but they are always the same size.

LAW 3: The squares of the periods of the planets are proportional to the cubes of their semimajor axes. A variation of law 2. Basically the closer the earth is to the sun the faster it rotates.

The beauty of Keplers laws is that in the mathematics the mass of the earth cancels out. So the only factors are the distance from the sun and the orbital speed. Mass doesn't matter. Sounds a little wierd I know, but it's the way the math works out. It's why we can have the earth in it's orbit where it is, jupiter with something like 300 time the mass of the earth way out there and pluto at .002 times the mass of the earth even further out. They just orbit slower based on their distance, not their mass.

[ImanCarrot]

The beauty of Keplers laws is that in the mathematics the mass of the earth cancels out

*confused* What if the earth's mass was equal to, or ten times that of the the sun then?

Or... if it had a mass of only 1 ounce that would surely affect it?

The orbit distance, and/ or speed of orbit would need to change surely *scratches head*

As I recall, Kinetic Energy= 1/2(MV^2) ... so increasing the mass would need a reduction in Velocity to maintain the Kinetic Energy. This doesn't sound right though....

Manual M and G code suddenly looks a lot easier now lol.

[Geof]

*confused* What if the earth's mass was equal to, or ten times that of the the sun then?...

In your second case the sun would orbit the earth.

In your first case both would orbit a point equidistant between them.

In all cases the centers of mass of each orbiting body actually orbit a point which corresponds to the center of mass of the combined system. I think for the moon-earth system it is a few thousand miles underground.

The dependence solely on distance is why a geosynchronous satellite has to orbit at the distance it does; 25,000 kilometers in round figures(I think ???). A satellite closer in goes faster, further out goes slower. You can calculate the geosynchronous distance like Arthur C. Clarke did in the 1950's. Just think how rich he would be if he had patented the idea!

EDIT: Manual G and M code is a whole lot easier; provided you can define the shapes analytically.

[ImanCarrot]

Manual G and M code is a whole lot easier; provided you can define the shapes analytically

hehe, try telling that to my machine: I can take days to programe a lens then the blasted thing will sometimes do what it wants... which is invariably the opposite to what I want it to do

It constantly amazes visitors to my lab that everytime I go to press the big green button I touch my lucky block of wood on the side of the machine "for good luck" mehehe.

[Geof]

...everytime I go to press the big green button I touch my lucky block of wood on the side of the machine "for good luck" mehehe.

I though the lucky block of wood was a given and did not ever need to be mentioned.

[martinw]

This is the simple answer from Kepler's laws pf planetary motion.......

They just orbit slower based on their distance, not their mass.

Dear Steven,

Sorry, I still don't get it. This ellipse thing is doing my head in. Could we just simplify the solar system temporarily in order for me to get to grips with the problem.......?

If you brushed all the planets (apart from the Earth) away into deepest space, would the Earth have a circular orbit about the Sun, or would it still be elliptical? My guess is elliptical. (OK, I would certainly hang on to the Moon because tides are quite handy for re-floating the boat after going aground.) Geof suggests that if the Earth and the Sun had the same mass, the orbits of each would be circular about a single point. Presumably a circle is a sub-set of ellipses?

Best wishes

Martin

[fizzissist]

Was it really a few cm??? I thought it was a fraction of a centimeter; certainly measurable but pretty small compared to the earth..

But what does it do to day length? This stuff coming in does not have the same angular momentum as the Earth so the spin will slow down. .

JPL reports that the "mean North pole" shifted approx. 2.5 centimeters in the direction of 145deg East Longitude, consistent with an observed long-term trend.

The day was also decreased by some 2.68 microseconds, suggesting that the earth is becoming more "round"...that is, there's less flattening on top and bulging at the equator.

[sdantonio]

Ok, see if this helps or is it more confusing?

[sdantonio]

Dear Steven,

Sorry, I still don't get it. This ellipse thing is doing my head in. Could we just simplify the solar system temporarily in order for me to get to grips with the problem.......?

If you brushed all the planets (apart from the Earth) away into deepest space, would the Earth have a circular orbit about the Sun, or would it still be elliptical? My guess is elliptical. (OK, I would certainly hang on to the Moon because tides are quite handy for re-floating the boat after going aground.) Geof suggests that if the Earth and the Sun had the same mass, the orbits of each would be circular about a single point. Presumably a circle is a sub-set of ellipses?

Best wishes

Martin

Hi Martin,

Yes, a circle is a specialized case of an ellipse where the focci are in the center. So yes it would still be an ellipse.

[sdantonio]

Oh yeah, regarding E=1/2MV^2

More importantly there is the law of conservation of momentum (p=MV)

momentum has to stay constant unless the planet is acted on by some perturbing force (like being hit by an asteroid or something big like that).

If mass increases then velocity has to decrease for momentum to stay the same, and momentum must stay the same. Momentum is what keeps the planet trying to go wizzing off into space. Gravity is what is trying to pull it into the sun. When they are balanced you have a stable orbit.

Now, if the earth collected enough dust to double in mass, then conservation of momentum says it's velocity much reduce to half making for a much longer year, but momentum remains constant. So the orbital distance stays the same (no difference in gravity pulling it in or momentum pulling it out).

that may help a bit too.

[sdantonio]

JPL reports that the "mean North pole" shifted approx. 2.5 centimeters in the direction of 145deg East Longitude, consistent with an observed long-term trend.

The day was also decreased by some 2.68 microseconds, suggesting that the earth is becoming more "round"...that is, there's less flattening on top and bulging at the equator.

Is that true north or magnetic north (which moves at a pretty steay rate anyway is I think is somewhere under one of the bays off northern Canada right now).

[sdantonio]

http://gsc.nrcan.gc.ca/geomag/nmp/long_mvt_nmp_e.php

Magnetic north movement

[martinw]

More importantly there is the law of conservation of momentum (p=MV)

momentum has to stay constant unless the planet is acted on by some perturbing force (like being hit by an asteroid or something big like that).

.

Dear Steven,

Thank-you for your help.

You say that momentum has to stay constant. Presumably this only applies within a closed system. By coming from outside the system, the asteroid provides a force to change the net amount of momentum.

Is this right?

Thanks

Best wishes

Martin

[sdantonio]

Dear Steven,

Thank-you for your help.

You say that momentum has to stay constant. Presumably this only applies within a closed system. By coming from outside the system, the asteroid provides a force to change the net amount of momentum.

Is this right?

Thanks

Best wishes

Martin

Yes, correct. Actually it's one of Newton's laws (#2 I think). An objects motion will remain constant unless acted upon by an outside force.

[martinw]

Yes, correct. Actually it's one of Newton's laws (#2 I think). An objects motion will remain constant unless acted upon by an outside force.

Dear Steven,

Thanks again.

OK, so if we start exporting "stuff" from the Earth to a position outside the Solar system, what happens to the Earth's orbit round the Sun?

Best wishes,

Martin