Are we lighter in the daytime?

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Re: Are we lighter in the daytime?

#141  Postby Fallible » Jan 02, 2015 5:22 pm

I was just about to say the same to you. :dopey:
John Grant wrote:They say 'let go, let go, let go, you must learn to let go'.
If I hear that fucking phrase again, this baby's gonna blow
Into a million itsy bitsy tiny pieces, don't you know,
Just like my favourite scene in Scanners .
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Re: Are we lighter in the daytime?

#142  Postby Veida » Jan 02, 2015 5:27 pm

DavidMcC wrote:
Veida wrote:
DavidMcC wrote:An important thing I missed out in this recent "debate" is that there is an equatorial bulge in the oceans, caused by the earth's rotation about its own axis,

Yes, that is true, but it doesn't change over time. So that is not relevant.

Nonsense. It is regukarly tilted up and down by the moon's pull. It seems like yoju have to study gyroscopes more.

So which equatorial bulges are you talking about? The one along the equator caused by the Earth's spin, or the two caused by the Moon that aren't neccessarily on the equator, or the two caused by the Sun that aren't neccessarily on the equator?

DavidMcC wrote:I was talking about the earth's oceans. They spin with the earth, but the plane of their spin can be tipped by the moon. It's a gyroscopic effect.

Speaking of misconceptions.
Last edited by Veida on Jan 02, 2015 5:33 pm, edited 1 time in total.
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Re: Are we lighter in the daytime?

#143  Postby Veida » Jan 02, 2015 5:31 pm

DavidMcC wrote:
Thommo wrote:Image

My point, exactly, but you have forgotten the implications for contact force (your weight). Thus, your account is inadequate.

I'm curious. If this picture is somehow related to your point - how do you explain the forces that increase the weight at the points midway between those closest to and farthest from the satellite? (Where the arrows are directed towards the center?)
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Re: Are we lighter in the daytime?

#144  Postby DavidMcC » Jan 02, 2015 5:44 pm

Veida wrote:
DavidMcC wrote:
Thommo wrote:Image

My point, exactly, but you have forgotten the implications for contact force (your weight). Thus, your account is inadequate.

I'm curious. If this picture is somehow related to your point - how do you explain the forces that increase the weight at the points midway between those closest to and farthest from the satellite? (Where the arrows are directed towards the center?)

Actually, I was about to correct myself. the diagram is over-simplstic, because it fails to recognise that the main cause of the bulge is the earth's spin. The moon only tips the plane of that spin. It does not create a separate bulge of its own.
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Re: Are we lighter in the daytime?

#145  Postby Veida » Jan 02, 2015 5:55 pm

Again. Which bulge? There are five bulges.

And what about those inward-directed arrows? How do you explain those?
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Re: Are we lighter in the daytime?

#146  Postby Thommo » Jan 02, 2015 5:55 pm

DavidMcC wrote:
Thommo wrote:Image

My point, exactly, but you have forgotten the implications for contact force (your weight). Thus, your account is inadequate.


This is a diagram of tidal force, relevant to both rotating and non rotating bodies. It in fact shows the exact opposite of what you asserted.

It is not an account of centrifugal force, which is offtopic and for which the cursory account I gave is perfectly adequate.

DavidMcC wrote:Actually, I was about to correct myself. the diagram is over-simplstic, because it fails to recognise that the main cause of the bulge is the earth's spin. The moon only tips the plane of that spin. It does not create a separate bulge of its own.


:picard:

It's a force diagram for tidal forces, not a force diagram for centrifugal force.
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Re: Are we lighter in the daytime?

#147  Postby DavidMcC » Jan 02, 2015 5:59 pm

Thommo wrote:
DavidMcC wrote:
Thommo wrote:Image

My point, exactly, but you have forgotten the implications for contact force (your weight). Thus, your account is inadequate.


This is a diagram of tidal force, relevant to both rotating and non rotating bodies. It in fact shows the exact opposite of what you asserted.

It is not an account of centrifugal force, which is offtopic and for which the cursory account I gave is perfectly adequate.

DavidMcC wrote:Actually, I was about to correct myself. the diagram is over-simplstic, because it fails to recognise that the main cause of the bulge is the earth's spin. The moon only tips the plane of that spin. It does not create a separate bulge of its own.


:picard:

It's a force diagram for tidal forces, not a force diagram for centrifugal force.

And that's why it doesn't tell the whole story. In the whole story, centrifugal force cannot be ignored - the earth's oceans are like a large, wet gyroscope.
One day, you'll understand that, but evidently not yet.
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Re: Are we lighter in the daytime?

#148  Postby Thommo » Jan 02, 2015 6:02 pm

DavidMcC wrote:And that's why it doesn't tell the whole story. In the whole story, centrifugal force cannot be ignored - the earth's oceans are like a large, wet gyroscope.
One day, you'll understand that, but evidently not yet.


Cannot be ignored for what? Considering the effect of tidal forces on non rotating bodies?

Because that's where your misunderstanding was, and in fact centrifugal forces (which are zero in that case) can indeed be ignored completely.

For some reason that isn't too clear you're trying to paint a reluctance to discuss the digression with some kind of ignorance or denialism. That couldn't be further from the truth.
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Re: Are we lighter in the daytime?

#149  Postby twistor59 » Jan 02, 2015 6:02 pm

Thommo wrote:
DavidMcC wrote:
Thommo wrote:Image

My point, exactly, but you have forgotten the implications for contact force (your weight). Thus, your account is inadequate.


This is a diagram of tidal force, relevant to both rotating and non rotating bodies. It in fact shows the exact opposite of what you asserted.

It is not an account of centrifugal force, which is offtopic and for which the cursory account I gave is perfectly adequate.

DavidMcC wrote:Actually, I was about to correct myself. the diagram is over-simplstic, because it fails to recognise that the main cause of the bulge is the earth's spin. The moon only tips the plane of that spin. It does not create a separate bulge of its own.


:picard:

It's a force diagram for tidal forces, not a force diagram for centrifugal force.


It reminded me of:

Image
A soul in tension that's learning to fly
Condition grounded but determined to try
Can't keep my eyes from the circling skies
Tongue-tied and twisted just an earthbound misfit, I
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Re: Are we lighter in the daytime?

#150  Postby campermon » Jan 02, 2015 6:44 pm

:rofl:
Scarlett and Ironclad wrote:Campermon,...a middle aged, middle class, Guardian reading, dad of four, knackered hippy, woolly jumper wearing wino and science teacher.
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