[damocles]

A bit of lateral thinking -- nothing to do with animal flatulence

If we arranged for every city in the Northern hemisphere to have a one-way traffic system where vehicles were constrained to work in a clockwise direction, and a similar system where every city in the Southern hemisphere forced vehicles to circulate in an anti-clockwise direction, we might make a much more substantial contribution to speeding up the earth's rotation!

Even if the road rules in North America and Europe changed to drive on the left, vehicles would travel clockwise around roundabouts, and that could contribute.

[Geezer]

vehicles would travel clockwise around roundabouts, and that could contribute.

Not in Italy or Boston. They would drive straight across the roundabouts there.

[Bored chemist]

Great analogy; I wonder if Geezer accepts it.

Almost, but not quite.

The bus was accelerated, therefore it was "made to move faster". Then it slowed down again and stopped.

However, the bus did not return to its original position, so we can't say the net effect was nil.

For an ideal, "physics question" type frictionless bus, the C of G of the bus/ bags/ school-kids system would end up in exactly the same place that it started.

So we can say the overall effect was practically nil (except that the bus would be slightly warmer and bigger afterwards).

The analogous effect of the cow farts would be that one day would be slightly shorter, but that for all subsequent days the day length would be the same. You would introduce a change in phase, but not frequency, of rotation.

Also, the vehicles on the roundabouts have the same problem. They are part of the earth/ air/ cow/ fart/ vehicle system, and can not influence the overall angular momentum of the system.
There would be short term effects, but they would stop when the cars stopped or left the roundabouts. In particular, most effects would be cancelled out when the vehicles drove home.

[damocles]

From Bored Chemist:

Also, the vehicles on the roundabouts have the same problem. They are part of the earth/ air/ cow/ fart/ vehicle system, and can not influence the overall angular momentum of the system.
There would be short term effects, but they would stop when the cars stopped or left the roundabouts. In particular, most effects would be cancelled out when the vehicles drove home.

NO, that is the whole point of the one way systems and roundabouts. The movement of traffic, both morning and evening, would have a continuing vorticity in the same direction that would have to be deducted from the conserved angular momentum of the earth's rotation on a continuing basis.

Angular momentum (earth + traffic) is conserved. SO if we manipulate angular momentum (traffic) on a continuing basis, we make a real and lasting change in angular momentum (earth).

The traffic flow could not alter the total angular momentum of the earth system as bored chemist rightly points out. But it could lengthen or shorten the day, because the traffic makes a contribution to the system angular momentum that is separate from and independent of the contribution from the earth's rotation.

[Geezer]

You would introduce a change in phase, but not frequency, of rotation.

Say what? How do you change phase without altering frequency?

[Bored chemist]

You would introduce a change in phase, but not frequency, of rotation.

Say what? How do you change phase without altering frequency?

I used to get up at 08:30 to go to work each day, but I changed my job.
Now I get up at 06:30.
That's a change in phase but it was always once a day so the frequency is the same.
The Sunrise does the same thing every day, it's once a day but the phase changes WRT noon.

The traffic will make a difference while it's in motion but if there's ever a moment when all the traffic stops - say the World cup final- then the speed of the earth will be just the same as it was before. Same with the cow farts, once they come to rest there's no effect on the spin.

As I said, if the cows faced East and started walking they would change the rotation rate slightly. The cars on roundabouts are much the same.

[Geezer]

I used to get up at 08:30 to go to work each day, but I changed my job.
Now I get up at 06:30.
That's a change in phase but it was always once a day so the frequency is the same.
The Sunrise does the same thing every day, it's once a day but the phase changes WRT noon.

Frequency is just the reciprocal of period (the interval between cyclic events). The interval had to change to produce a change in phase. Mathematically, it's impossible to change the period without changing the frequency.

The change in frequency may have been temporary, but it still had to change to produce a change in phase.

[Bored chemist]

If you picked the right day then the change in period was 2 hours in one day- about 8%.
If you loot at it over the course of a week then it's just over 1%. That year the average change was about 0.02%.
But this is a one off event so you have to average it over the whole of time. The mean change in frequency was zero.
Also, something that happens at 06:30 one day, but at 08:30 the next isn't a "cyclic event" because it doesn't repeat; It's not cyclical.

[Geezer]

Yes, but the frequency still changed.

[Bored chemist]

Yes, it changed by zero.

[Geezer]

Yes, it changed by zero.

Ah, right! You must be using the "new math" then. Either that or you have some previously unknown proof that frequency and period are not reciprocals up your sleeve, or perhaps you believe the period didn't actually change?

[Bored chemist]

OK, it was 1/86400Hz before and it was 1/86400Hz afterwards.
What does old maths give as the difference between those?

There was a change, but that was a one off event; it doesn't have a frequency (unless you count zero).

[Geezer]

OK, it was 1/86400Hz before and it was 1/86400Hz afterwards.
What does old maths give as the difference between those?

There was a change, but that was a one off event; it doesn't have a frequency (unless you count zero).

Perhaps you are thinking that frequency can only be determined by timing entire cycles? That's not necessary. We only need to know angular velocity.

If we plot the angular velocity against time and do a Fourier transform on it, we'll see lots of interesting changes in frequency when the angular velocity is changing.

[Bored chemist]

What apodisation did you plan to use for the FT?

[Geezer]

What apodisation did you plan to use for the FT?

Enough to prove that the frequency changed.

[Bored chemist]

What apodisation did you plan to use for the FT?

Enough to prove that the frequency changed.

Please show your working

My hypothetical change of job happened on April 1st this year so, in a sense, rather than being 24 hrs long, that day was just 22 hrs.
Now, you can do an FT on a pulse lasting 22 hrs and come out with a nice "spectrum". If I remember rightly it comes out as a sinc function. Sure, it will have a dominant component at a frequency of 1/22 hrs^-1, but that's just a mathematical result.
It doesn't have a meaning.
There is no way that you can say that April 1 2011 has a frequency of "every 22 hrs" because it doesn't repeat itself.
It actually has a frequency of once in the whole of time.
1/ infinity is practically zero.

[Geezer]

Please show your working

I've got a better idea. You show how frequency is not the reciprocal of period.

[Geezer]

BTW BC, your "change in job" analogy is a load of twaddle a bit suspect.

The Earth's frequency is a function of its angular velocity. The time at which you start work has nothing to do with your angular velocity, so there was no phase shift in that case.
 

[Airthumbs (OP)]

The Earth's frequency is a function of its angular velocity. The time at which you start work has nothing to do with your angular velocity, so there was no phase shift in that case.

The Earth's frequency... is that the Schumann thingy me bob?  Angular velocity, sounds like the kind of math you would need to determine the outcome of my original post which has somewhat drifted a wee bit, not that I mind as to be honest this thread was destined for the manure heap from it's conception.  98, 99 100....  []

[Bored chemist]

Something that happens once, and only once doesn't have a frequency. It doesn't matter how long it takes, Only things that repeat have a meaningful frequency.
My granny may have lived for a hundred years, but she didn't live ten times per millennium.

And I'm sorry you don't understand that my working day and the earth's rotation have a simple fixed phase relation, except once when I changed it.
I used to get up at 08:30, that's about 60 degrees of the earth's rotation before the Sun is overhead. Now I get up at 06:30; that's about 90 degrees before noon. (I'm ignoring the half hours to keep the arithmetic easy.)
The change of 30 degrees is a real phase shift.
(obviously I'm simplifying it by also ignoring weekends, BST, and such)