[evan_au]

Anyway, must get everything battened down and go over today’s passage plan.

And roughly where are you sailing, if you don't mind telling us?

[gem (OP)]

Hi all,

So Halc,

The yacht carries no force. If it isn't accelerating, then the net force exerted by (or on) it is zero. 10,000 kg * 4 = 40,000 kg•m/s, not 40,000 N. Getting the units right is half the story. The force exerted on Earth by solar wind/light seems pretty irrelevant to this since it is nicely balanced by gravity in the opposite direction. The sun's direct contribution is energy, not momentum.

The force exerted by your 40t yacht on collision depends on how much it crumples on impact.

If you look back I used the correct units of momentum, and when putting the argument as to help scale the implications as to the equivalence of this, the continual force of the radiation pressure applied to the cross sectional area of the Earth
rather than just Numbers to powers of 10 that many would struggle to put a real life value to.
 
( F = radiation pressure x area )   units:Newtons

which I gave an example of being less than one super tanker continually colliding spread across the CSA. 

Again, if the boat isn't accelerating, then no momentum transfer at all is needed to keep it thus. It just needs energy input to maintain the speed.

What form of energy is required for a sailing boat ?

kinetic energy = 1/2 x mass x velocity^2    momentum = mass x velocity, difficult to separate them, so to keep the boat at a constant velocity a constant momentum transfer from the atmosphere is required.

To dismiss convection you state Halc ; my bold

Irrelevant to why the boat sails through the water. Convection occurs because the sun heats stuff, making it move around, which explains why there's wind, but not how the wind makes the boat go. In the simplified example, there's just a massive wad of air moving with its own inertia. It's a closed system, so no input of any kind.

I think you just made quite a good case for the source of Colin's sailing boats, momentum. especially as we know it isnt a closed system and there is an input.

Also Halc, I believe BC already covered the day/night aspect and the Suns input you are happy to put to one side.

I just ignored it since it has no immediate direct effect, else sailing would be impossible at night.

I

Heat may radiate away, but momentum doesn't

I'm afraid that's not true either, I believe ES covered aspects of that.

Colin I hope your having a great time.

However, I don’t think that’s what gem is after. I think he wants to prove that momentum is not conserved in the earth atmospheric system, but I haven’t yet seen him clearly define what the closed system is that he wants to consider, perhaps I’ve missed it.

Yes your partially correct because I don't see a closed system.

However this is only a preamble that links to several other phenomena,

I suppose current theory needs to state, where the action reaction pairing occurs due to the spontaneous convection occurring in the earths uncoupled atmosphere.

Given the motion/momentum generated, impacts things like sail boats mountains trees. and oceans, with varying degrees of inelastic collisions that would alter the vector total expected from a closed system.
because the solid earth cannot discriminate between these collision and a meteorite, in regards to the potential change of momentum.

[Halc]

You are repeating the same mistakes, so it appears that your goal is to assert nonsense rather than learn anything.
My contribution to the thread is about how wind makes a sailboat go and not about how how much momentum of Earth is or isn't preserved in the presence of the sun.

Earth is a system, but hardly a closed one. There is very much energy continuously going in and out of Earth. Momentum is constantly changing. Mass is even changing. Nobody claims it is a closed system. Hence my terse hand-wave that the radiance of the sun is primarily responsible for wind.
There is also significant wind on Jupiter, which is not mostly due to the sun's radiance, so wind very much can form in a closed system.

If you look back I used the correct units of momentum

10 metric tonnes of 40 ft sailing yacht traveling at 4 m/s of 40 x10^3 N

You specified Newtons, which is mass•distance/sec² whereas momentum is mass•distance/sec.

A sailboat moving at a constant 4 m/sec has zero acceleration. Remember F=ma, taught when you were 12? If 'a' is zero, so is F. If acceleration is zero, then velocity is constant, and therefore zero momentum transfer from the boat to the rest of the system.

What form of energy is required for a sailing boat ?

kinetic energy = 1/2 x mass x velocity^2    momentum = mass x velocity, difficult to separate them

They're very separate things. Difficult to combine them, but you manage to do it, with the resulting nonsense. But KE is probably inappropriate since the boat is neither gaining nor losing KE, just as it is neither gaining nor losing momentum.
So the way to analyze it is to demonstrate that the forces acting on it must add up to zero. Those forces, individually, represent work, not KE. So the form of energy required for a sailing boat is better expressed as work done on it.

to keep the boat at a constant velocity a constant momentum transfer from the atmosphere is required.

But no momentum transfer to or from the boat, whose momentum is constant since both its mass and velocity are constant. So any momentum transferred to the atmosphere must come from somewhere other than the boat.

momentum. especially as we know it isnt a closed system and there is an input.

'Momentum' doesn't define a system, closed or otherwise.

[gem (OP)]

Hi all,
Halc
Please take a look at post 13 I believe the units are correct given:
The longer the electromagnetic wave is incident on the object, the more momentum is transferred. This time dependence complicates matters, though, so it can be defined where it does not depend on time, this is called radiation pressure, N/m^2

Halc

Remember F=ma, taught when you were 12? If 'a' is zero, so is F. If acceleration is zero,

Maybe you should have put net into the point

Also can be written as F = rate of change of momentum !


Halc

But no momentum transfer to or from the boat, whose momentum is constant since both its mass and velocity are constant. So any momentum transferred to the atmosphere must come from somewhere other than the boat

Now Halc we are considering a dynamical real world interaction, where there is a continuous exchange of energy and momentum to allow a sailing boat to maintain a constant velocity through the fluids, Indeed friction is a consequence of the momentum being transferred, in these inelastic therefore not Isentropic interactions

Halc what you did here by misquoting me, I believe is disingenuous and doesn't reflect well on you, at least you left the full stop in. 

(gem quoted by Halc)     (momentum. especially as we know it isnt a closed system and there is an input.)
Halcs comment
'Momentum' doesn't define a system, closed or otherwise.

Now I believe the pertinent point to be addressed is:

gem

I suppose current theory needs to state, where the action reaction pairing occurs due to the spontaneous convection occurring in the earths uncoupled atmosphere.

Given the motion/momentum generated, impacts things like sail boats mountains trees. and oceans, with varying degrees of inelastic collisions that would alter the vector total expected from a closed system.
because the solid earth cannot discriminate between these collision and a meteorite, in regards to the potential change of momentum.

[Halc]

Please take a look at post 13 I believe the units are correct given

OK. I admit I probably had never read post 13. I can comment on that if you like.

So lets assume as suggested the source of the kinetic energy is the Suns electromagnetic radiation

I agree that the majority of the energy driving the wind comes from this energy source, but EM radiation from the sun is not in the form of KE. It gets translated to that in a complicated and chaotic process.

assume a speed over ground of 4 m/s therefore for every kilogram mass of the boat we have
kinetic energy of 8.0 Joules and corresponding momentum of 4.0 Kg m/s

That is correct units, yes. Not sure why you changed it to force in a later post.

... this gives a momentum pressure of between 3.33 x 10^-6 N/m^2  and 6.67 x 10^-6 N/m^2
depending on full absorption to perfect reflection, of the light energy received.

That pressure is countered by a much larger force in the opposite direction which is why Earth acceleration vector is towards the sun and not away from it. After a full year, the Earth is right were it was before and at the same velocity, so this continuous force (by radiation pressure, gravity, other effects) has no cumulative effect on the KE or momentum of Earth It isn't the cause of the wind, whereas the radiant energy is, but that also is the source of (most of) the eventual KE energy of my car, not just the sailboat. Likewise, the continuous 4 million N force on the ISS adds no KE to it. This is why I suggest analyzing the effects of force in terms of work.

where did the mass of the boat get this momentum from.

If it's moving at a constant 4 m/s, it already has it. The source is itself. You don't seem to be considering the case where it gets going from a stop, but even then, the source of momentum is pretty obvious, and it isn't the sun at all.

Maybe you should have put net into the point
Also can be written as F = rate of change of momentum !

OK, net F = rate of change of momentum. And net F on the sailboat is nada, so no momentum change.

But no momentum transfer to or from the boat, whose momentum is constant since both its mass and velocity are constant. So any momentum transferred to the atmosphere must come from somewhere other than the boat

Now Halc we are considering a dynamical real world interaction, where there is a continuous exchange of energy and momentum to allow a sailing boat to maintain a constant velocity through the fluids

There might be a net exchange of energy and momentum going on, but neither net exchange is with the boat which has zero change in both. You seem to both assert this but then not realize it.

Indeed friction is a consequence of the momentum being transferred, in these inelastic therefore not Isentropic interactions

OK, but I was not discussing entropy.

Halc what you did here by misquoting me, I believe is disingenuous and doesn't reflect well on you, at least you left the full stop in.

OK. It appeared to me that you were using the word momentum as a description of a system, in this statement:

I think you just made quite a good case for the source of Colin's sailing boats, momentum. especially as we know it isnt a closed system and there is an input.

Both 'sentences' admittedly do not parse, and I interpreted it incorrectly. No clue what you meant by the two fragments, neither of which is a well formed sentence. The word 'momentum' doesn't seem to fit in at all with any of it.
If you're saying the boat isn't a closed system, then we all agree with that.

I suppose current theory needs to state, where the action reaction pairing occurs due to the spontaneous convection occurring in the earths uncoupled atmosphere.

This is complicated, but the basics are not hard to comprehend. It involves heat, buoyancy, friction, and Coriolis effects. The model allows Earth to be approximated as a closed system to momentum in its own frame, especially if we remove tidal effects, which is a very real and continuous external torque on the system. External things like meteors have negligible effect since they for the most part cancel each other out. Of course it cannot be closed to energy.

[gem (OP)]

Hi all

Ok  lets focus on what I posted as to what I believe is pertinent, for current theory to remain.

gem

I suppose current theory needs to state, where the action reaction pairing occurs due to the spontaneous convection occurring in the earths uncoupled atmosphere.

Given the motion/momentum generated, impacts things like sail boats mountains trees. and oceans, with varying degrees of inelastic collisions that would alter the vector total expected from a closed system.
because the solid earth cannot discriminate between these collision and a meteorite, in regards to the potential change of momentum.

Halc

This is complicated, but the basics are not hard to comprehend. It involves heat, buoyancy, friction, and Coriolis effects. The model allows Earth to be approximated as a closed system to momentum in its own frame, especially if we remove tidal effects, which is a very real and continuous external torque on the system. External things like meteors have negligible effect since they for the most part cancel each other out. Of course it cannot be closed to energy.

I agree the dynamics are complicated, so lets bring it back to the basic points I made in the statement above,

where is the action reaction pairing that causes the fluid flow that occurs spontaneously actually occurring ?

And does that location allow the solid earth to discriminate between these consequential collisions and a meteorite's collision, in regards to the potential change of momentum ?

If it cannot be categorically stated otherwise then we will have to look at the questions this raises, for example appearance of neutrality/canceling of the effect of these frictional forces as Halc attributed to the meteors collisions, also external torque forces, and apparent stability of length of day.


For example can the knowledge of the known external torques predict specific dates the earth rotation will be slower/faster than the day before/after ?

[Colin2B]

I suppose current theory needs to state, where the action reaction pairing occurs due to the spontaneous convection occurring in the earths uncoupled atmosphere.

Not sure what you mean by this

For example can the knowledge of the known external torques predict specific dates the earth rotation will be slower/faster than the day before/after ?

Not sure what external torques you mean, but if you are interested in rotational variability this is the go to guy, done a lot of work on it, but I’m not sure about forecasts because of the huge variations involved. This is a layman intro:
https://syrte.obspm.fr/astro/journees2019/FILES/salstein.pdf

By the way, note that this is due to the transfer of momentum, not the creation of momentum, due to interaction at earth/atmosphere boundary etc.

[evan_au]

A similar question for landlubbers about "where wind force, energy and momentum come from"  got turned into a $10,000 bet:
See (18 minutes):

PS: Veritassium is a good series of sciency Youtube videos...

[Colin2B]

A similar question for landlubbers about "where wind force, energy and momentum come from"  got turned into a $10,000 bet:

I did notice there was a thread on this but I didn’t have time to follow it through in detail.
The centre of effort is a bit high for a boat, which has triangular sails to keep the centre of effort low, otherwise you get a lot of heeling and reduced effective sail area. I suspect a boat would also start to dig her nose in when on a run.

[gem (OP)]

Hi all,
thanks for the link Colin, you said you were not to sure of a couple of points I made, below is an extract from the paper you linked to.

D. SALSTEIN
my bold

ABSTRACT. It was noted some time ago that the angular momentum of the atmosphere varies,
both regionally as well as in total. Given the conservation of angular momentum in the Earth system,
except for known external torques, such variability implies transfer of the angular momentum across
the atmosphere’s lower boundary. As nearly all is absorbed by the Earth below, the solid Earth
changes its overall rotation from this impact

So for conservation of the angular momentum of the earth system to underpin the current theory.
 
I believe the current theory needs to state, where the action reaction pairing occurs due to the spontaneous convection occurring in the earths uncoupled atmosphere.

Given the motion/momentum generated, impacts things like sail boats mountains trees. and oceans, with varying degrees of inelastic collisions that would alter the vector total expected from a closed/conserved system.
because the solid earth cannot discriminate between these collision and a meteorite, in regards to the potential change of momentum, if the initial, action reaction occurs independently of the earths surface/crust.

Also Colin you state;

By the way, note that this is due to the transfer of momentum, not the creation of momentum, due to interaction at earth/atmosphere boundary etc.

Do you believe these transfers are fully elastic or fully inelastic with the surface /atmosphere ?
Do you believe you utilized any of the earths conserved systems angular momentum with your sailing boat  ?
Does convection alter the velocity of the atmosphere ?   

[Colin2B]

Do you believe you utilized any of the earths conserved systems angular momentum with your sailing boat  ?

From the point of view of the paper I linked to the boat is part of the earth/atmosphere system.

Does convection alter the velocity of the atmosphere ?

Velocity yes, but that’s not implying a change of total momentum. Remember what goes up comes down in atmospheric circulation.
If we fill a container with water and heat a bottom corner water will rise up one side and circulate in the container, if that container is suspended freely it will rotate in the opposite direction conserving the original 0 angular momentum. If the container is in contact with the earth the total momentum will remain 0 as it will transfer momentum to the earth, but I doubt the earth notices.

My own interest in the earth/atmosphere interface is only that the coefficient of friction varies over the earth surface which leads to wind shifts due to a combination of pressure systems, laminar flow and Coriolis effect. As you might guess I’m interested in predicting those effects locally.

[gem (OP)]

Hi all,

OK lets run with that analogy,
Colin

If we fill a container with water and heat a bottom corner water will rise up one side and circulate in the container, if that container is suspended freely it will rotate in the opposite direction conserving the original 0 angular momentum

First I would like to check I understand your description, if a fluid circulates in vessel, are you saying the vessel will rotate in the opposite direction ? for example if I set a fluid(water) rotating in a container half full of water and then sat it in a body of water the vessel would naturally rotate in the opposite direction ?
 

[gem (OP)]

Hi all,

Also given the Coriolis effect in the atmosphere transporting the momentum that was once a property of the solid earth, how is this momentum perfectly transferred back, to the solid earth as measured by LOD,  and not transferred to internal momentum of the elements that make up the fluid of the atmosphere.

Also How is this internal momentum of the atmosphere different from the internal momentum caused by the suns radiation. 

Also where does the momentum of sound come from and go to ?

why did the LOD get shorter yesterday will today and tomorrow ? 

 

[Halc]

First I would like to check I understand your description, if a fluid circulates in vessel, are you saying the vessel will rotate in the opposite direction ?

If 1) the vessel/water system had zero angular momentum before the heat was applied, and 2) no external torque is applied, then yes, rotation of the water one way must rotate the vessel the other way to maintain zero angular momentum. You can't change the total to a different number.

for example if I set a fluid(water) rotating in a container half full of water and then sat it in a body of water, the vessel would naturally rotate in the opposite direction ?

Sounds like the water already had angular momentum to start with in this case. No, the vessel has no reason to then rotate the other way.
If the vessel/water system was all stopped, and then a little internal propeller attached to the vessel started to rotate the water clockwise, then yes, the vessel would rotate counterclockwise due to the equal/opposite reaction of the propeller thingy attached to it.

Also given the Coriolis effect in the atmosphere transporting the momentum that was once a property of the solid earth

Coriolis effect has no direct effect on the total momentum of anything. Coriolis effects in the atmosphere is neither caused by nor causes any net force on Earth.  If Earth (the interface between ground and air) was perfectly frictionless, Coriolis effect would still make nice hurricanes with distinct eyes and such. Probably more so since said friction lessens the severity of such storms.

Also How is this internal momentum of the atmosphere different from the internal momentum caused by the suns radiation.

One is (considerable) momentum (mostly angular) already a property of a system (atmosphere) and the other is a mild transfer (almost none of which is angular) which nets pretty much zero momentum over a year.

Also where does the momentum of sound come from and go to ?

Sound doesn't have significant momentum. A shock wave does. Regular ocean waves don't push on the continents more than still water does, but tsunamis do. The latter is a shock wave.

why did the LOD get shorter yesterday will today and tomorrow ?

It probably got longer, but the day to day variations can go either way, probably not due to any forces applied by the atmosphere. It definitely gets longer over time. It used to be well under 10 hours.

[gem (OP)]

 

Hi all,

Ok Halc to cover those points.


Halc

If 1) the vessel/water system had zero angular momentum before the heat was applied, and 2) no external torque is applied, then yes, rotation of the water one way must rotate the vessel the other way to maintain zero angular momentum. You can't change the total to a different number.

I'm not sure this is achievable, in reality couldnt it be argued the vector sum is zero if they all/both go round in the same direction ?

Halc

Sounds like the water already had angular momentum to start with in this case. No, the vessel has no reason to then rotate the other way.
If the vessel/water system was all stopped, and then a little internal propeller attached to the vessel started to rotate the water clockwise, then yes, the vessel would rotate counterclockwise due to the equal/opposite reaction of the propeller thingy attached to it.

The internal propeller attached to the vessel sounds suspiciously a bit like a boat and does not replicate the action reaction pairing of convection.

Halc

Coriolis effect has no direct effect on the total momentum of anything. Coriolis effects in the atmosphere is neither caused by nor causes any net force on Earth.  If Earth (the interface between ground and air) was perfectly frictionless, Coriolis effect would still make nice hurricanes with distinct eyes and such. Probably more so since said friction lessens the severity of such storms.

Yes as I said momentum transported and transferred, but is it a 100% exchange rate ?  is there the consequence of transfer to momentum of the molecules and bonds thereof ? (internal momentum )

Which is the context of the point made previously which the following doesn't address. 
Halc

One is (considerable) momentum (mostly angular) already a property of a system (atmosphere) and the other is a mild transfer (almost none of which is angular) which nets pretty much zero momentum over a year.

Halc
.

Sound doesn't have significant momentum. A shock wave does. Regular ocean waves don't push on the continents more than still water does, but tsunamis do. The latter is a shock wave.

wave momentum =energy/phase velocity         so not sure how that fits with your statement   ?     

It probably got longer, but the day to day variations can go either way, probably not due to any forces applied by the atmosphere. It definitely gets longer over time. It used to be well under 10 hours.

 

https://syrte.obspm.fr/astro/journees2019/FILES/salstein.pdf


You are disagreeing with the go to guy according to Colin, regarding the predictions to LOD  I will post the results once they are published.

[Colin2B]

Thus I must throw a wrench into the statement from @Colin2B :

If we fill a container with water and heat a bottom corner water will rise up one side and circulate in the container, if that container is suspended freely it will rotate in the opposite direction conserving the original 0 angular momentum.

While I agree, I don't think it is possible for the container to be 'suspended freely'. It can be done in zero g of course, but in that case, heating part of it isn't going to result in rotation of the liquid.

You beat me to the spanner @Halc
Almost immediately after posting it I began to wonder ‘how’, but let it stand while thinking through.

I dismissed putting a fan inside as that is a clear force against the container. There is the added problem that with a fan the water density distribution stays constant whereas in a heated system it does not so the centre of mass changes so a gimbal at the original centre of mass won't work.
It’s also not possible (practically) to have a frictionless vessel/water interface, so water motion should pull the container around; and as you say, finding a way to suspend eg a sphere, without friction is difficult.
I’m still thinking about it 

I originally was going to suggest the jar as a model of a Hadley cell.

The only suggestion I have seen of sun heat increasing earth/atmosphere angular momentum was in a paper on extreme weather events and the effect on earth rotation. The discussion was around the effect of greater CO₂ leading to a change of mass distribution in the atmosphere.
All other changes to earth rotation are due to friction forces, and pressure differentials across mountain ranges transferring momentum from atmosphere and ‘tuther way round.

EDIT:

You are disagreeing with the go to guy according to Colin, regarding the predictions to LOD  I will post the results once they are published.

I’m not an expert in this area, my interest is strictly amateur although I’ve taken a number of courses in meteorology and sat in on some university courses. So I’m working on recommendations, and he does seem to be backing his work with actual measurements from satellite data etc.

[gem (OP)]

Hi all,

Halc / Colin, thank you for your candor,

In regards to the link you provided Colin, I would comment it is probably the best précis of current theory I have read.

However when you state your not an expert in this field I believe an inspection of the fundamentals that underpin current theory as stated in the abstract will be sufficient.

was noted some time ago that the angular momentum of the atmosphere varies,
both regionally as well as in total. Given the conservation of angular momentum in the Earth system,
except for known external torques, such variability implies transfer of the angular momentum across
the atmosphere’s lower boundary.

https://syrte.obspm.fr/astro/journees2019/FILES/salstein.pdf

Halc I would comment on the bonds between molecules as being an aspect of freedom of movement (vibration rotation and hydrogen bonds ) which will be a factor of density change when energy is gained/lost.

On the scenario of the rotation of the container needing to go the opposite way to conserve momentum of the system, there are probably experiments that could be done to test the principle, but it will come back to my earlier comments, of the action reaction pairing.

In regards to the detectability of the frictional interactions I would point you to the link provided.

If momentum is generated in the atmosphere independently of the solid earth then the current theory is flawed given the subsequent frictional transfers.





 

[gem (OP)]

Hi all,

Halc
I think your skipping about a bit with this, it appears on one hand your saying an atmosphere can have momentum from energy input/electromagnetic radiation due to convection, where none previously existed.
Then also stating that violates basic physics.

Anyway as stated earlier predictions for LOD

gem;on: 17/08/2021 23:57:41

why did the LOD get shorter yesterday will today and tomorrow ?

Length of day variations/fluctuations in milli seconds as published today for the relevant dates.   ( - = minus )

15/08/2021  - 0.4058
16/08/2021  - 0.6633
17/08/2021  - 0.9998
18/08/2021  - 1.0715

[Halc]

I think your skipping about a bit with this, it appears on one hand your saying an atmosphere can have momentum from energy input/electromagnetic radiation due to convection, where none previously existed.

Yea, if it transfers momentum from something else.

Then also stating that violates basic physics.

No, I said your statement (momentum change without transfer from something else) is the violation.

Anyway as stated earlier predictions for LOD
gem;on: 17/08/2021 23:57:41

why did the LOD get shorter yesterday will today and tomorrow ?

Length of day variations/fluctuations in milli seconds as published today for the relevant dates.   ( - = minus )

15/08/2021  - 0.4058
16/08/2021  - 0.6633
17/08/2021  - 0.9998
18/08/2021  - 1.0715

These are length of solar day, which get shorter this time of every year due to our orbit not being perfectly circular. This is purely a visual effect, not an actual delta in the spin rate.

I was talking about the spin rate, the sidereal rate, the time it takes to revolve exactly 360°, which is the rate from which the angular momentum is computed. This is a thread about momentum, not about when the sun appears to rise.

We both should have been more clear it seems.

[gem (OP)]

Hi all,

Ok to address your point;

Halc

These are length of solar day, which get shorter this time of every year due to our orbit not being perfectly circular. This is purely a visual effect, not an actual delta in the spin rate.

I was talking about the spin rate, the sidereal rate, the time it takes to revolve exactly 360°, which is the rate from which the angular momentum is computed. This is a thread about momentum, not about when the sun appears to rise.

We both should have been more clear it seems.

I'm afraid your mistaken, for example, the earth rotation ( LOD ) was actually slowing down between the 5th to the 13 th of august,

and the published values I posted are from :

 LOD - FINALS.DAILY (IAU1980) from the IERS



So I repeat my previous post.

gem

why did the LOD get shorter yesterday will today and tomorrow ?

Length of day variations/fluctuations in milli seconds as published today for the relevant dates.   ( - = minus )

15/08/2021  - 0.4058
16/08/2021  - 0.6633
17/08/2021  - 0.9998
18/08/2021  - 1.0715