| Topic: |
Science > Physics |
| User: |
"Nishu" |
| Date: |
26 Apr 2006 02:15:50 AM |
| Object: |
Are we heavier at night? |
At noon, the sun and earth pull the objects on the earth's surface in
opposite directions. At midnight the sun and earth pull these objects
in same direction. Does it mean weight of the object increases at
night??
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| User: "CWatters" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 09:43:17 AM |
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"Nishu" <amitk_dni@yahoo.co.in> wrote in message
news:1146035750.353397.149180@e56g2000cwe.googlegroups.com...
At noon, the sun and earth pull the objects on the earth's surface in
opposite directions. At midnight the sun and earth pull these objects
in same direction. Does it mean weight of the object increases at
night??
No because objects on the earth are in free fall around the sun just as
satellites are in free fall around the earth.
Of course you could argue that one side of the planet is _further_ from the
sun than the other - but that effect is going to be small.
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| User: "" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 03:18:18 AM |
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Nice question, I hope it's not homework.
Suppose no earth, then we are just in free fall around the sun, i.e.
weightless.
The existence of the earth is irrelevant from this point of view (no
gravitational shielding), therefore the answer is no. This much seems
certain.
My amateur guess: Note incidentally that there is a tidal effect on
the earth's shape, which does affect the measured gravity (as measured
by instruments called gravimeters). However high lunar tide can occur
day or night. The solar tide, about 1/2 the lunar tide in strength,
does synch with the day night cycle and will also affect your weight,
but there are two solar tides a day, not one (Gallileo's error). So
the answer might be yes, but not for the reason you suspected.
If this is right, I would appreciate confirmation by experts.
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| User: "" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 03:32:28 AM |
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free fall- In other words, the gravitational attraction on you of the
sun is exactly compensated by the centrifugal force of the earth's and
your orbital motion around the sun.
Homework for MIT first year students: Compute or look up the
magnitudes of these effects.
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| User: "Edward Green" |
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| Title: Re: Are we heavier at night? |
29 Apr 2006 11:18:11 AM |
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Nishu wrote:
At noon, the sun and earth pull the objects on the earth's surface in
opposite directions. At midnight the sun and earth pull these objects
in same direction. Does it mean weight of the object increases at
night??
That is a good question.
Assume the center of the Earth is in a circular orbit around the sun,
and neglect the planet's daily rotation. Now, when we are on (the
center of) the night side of the Earth, we are farther from the sun by
r, the Earth's radius, although we are orbiting it with the same w
(angular velocity). Therefore the sun's gravity is weaker while our
required acceleration is stronger (Rw^2), and we are not in a stable
orbit. Considering the effect of the sun alone, we would fly off the
surface of the Earth. Next consider that we are on the day side.
Inverting the argument, the required gravitational acceleration to keep
us in orbit for that radius and w is smaller, while the sun's gravity
is larger. So we should tend to fly off the surface of the Earth on
this side also, given the effect of the sun alone.
Are the effects in fact equal and opposite? Centripetal acceleration
in a circular orbit is Rw^2, linear in the orbital radius, whereas the
effect of the sun's gravity goes as 1/R^2. However, r/R ~ 0.4 10^(-4),
so it appears taking the variation of gravity with orbital radius over
this perturbation as linear is a good approximation. We may correct
for this, but it's not clear a priori that effects from other sources
of error in the first model aren't commensurate.
Conclusion: no simple prediction. Empirically, any such effect must be
very small, because I have never heard that it makes any difference to
a spring scale whether we measure at noon or midnight! Of course
balance scales would see no effect.
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| User: "" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 08:05:52 PM |
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OK ,great, plenty of theories.
(Well, not quite, those who predict some change in weight should at
least *try* to predict the magnitude). After all, this is
sci.physics.
What about experiment?
Well, g is about 980 cm/sec^2 or 980 gals (for galilleos) where 1 gal =
1cm/sec^2.
The tidal variation is up to 300 microgals = 0.3 milligals = 3 x
10^(-4) cm/sec^2.
After all the corrections are done (see
http://www.earthsci.unimelb.edu.au/ES304/MODULES/GRAV/NOTES/factors.html
)
the residuals are about 0.1 microgals or about 10^(-10) earth
gravities, without any allowance for the durnal effects mentioned
below. So the question for those predicting a change is, how big a
change do you expect to see?
Notice, no ad hominum arguments, just calculations are required now.
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| User: "tadchem" |
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| Title: Re: Are we heavier at night? |
27 Apr 2006 04:13:04 AM |
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wrote:
OK ,great, plenty of theories.
(Well, not quite, those who predict some change in weight should at
least *try* to predict the magnitude).
Tide raising force f (actually an acceleration) of a mass M (in units
of the earth's mass) at a distance R (in units of the earth's radius):
f = g*M*(2R-1)/[R*2*(R-1)^2)]
For large R,
f/g = 2*M/R^2
For the moon f/g = 1/8,800,000 (maximum, may be as little as
1/11,700,000). For the sun f/g = 1/19,300,000.
After all, this is
sci.physics.
What about experiment?
Michelson, 1913.
Well, g is about 980 cm/sec^2 or 980 gals (for galilleos) where 1 gal =
1cm/sec^2.
The tidal variation is up to 300 microgals = 0.3 milligals = 3 x
10^(-4) cm/sec^2.
After all the corrections are done (see
http://www.earthsci.unimelb.edu.au/ES304/MODULES/GRAV/NOTES/factors.html
)
the residuals are about 0.1 microgals or about 10^(-10) earth
gravities, without any allowance for the durnal effects mentioned
below. So the question for those predicting a change is, how big a
change do you expect to see?
Michelson saw a tide of <0.001 inch in a 500 foot pipe.
Tom Davidson
Richmond, VA
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| User: "tadchem" |
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| Title: Re: Are we heavier at night? |
27 Apr 2006 04:02:43 AM |
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wrote:
OK ,great, plenty of theories.
(Well, not quite, those who predict some change in weight should at
least *try* to predict the magnitude). After all, this is
sci.physics.
What about experiment?
Well, g is about 980 cm/sec^2 or 980 gals (for galilleos) where 1 gal =
1cm/sec^2.
The tidal variation is up to 300 microgals = 0.3 milligals = 3 x
10^(-4) cm/sec^2.
After all the corrections are done (see
http://www.earthsci.unimelb.edu.au/ES304/MODULES/GRAV/NOTES/factors.html
)
the residuals are about 0.1 microgals or about 10^(-10) earth
gravities, without any allowance for the durnal effects mentioned
below. So the question for those predicting a change is, how big a
change do you expect to see?
Notice, no ad hominum arguments, just calculations are required now.
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| User: "Jan Pantelje" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 07:19:40 AM |
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On a sunny day (26 Apr 2006 00:15:50 -0700) it happened "Nishu"
<amitk_dni@yahoo.co.in> wrote in
<1146035750.353397.149180@e56g2000cwe.googlegroups.com>:
At noon, the sun and earth pull the objects on the earth's surface in
opposite directions. At midnight the sun and earth pull these objects
in same direction. Does it mean weight of the object increases at
night??
Probably we lay down at night because we are pullede harder towards the ground ;-)
Look correct to me though.
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| User: "Sam Wormley" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 08:58:42 AM |
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Jan Pantelje wrote:
On a sunny day (26 Apr 2006 00:15:50 -0700) it happened "Nishu"
<amitk_dni@yahoo.co.in> wrote in
<1146035750.353397.149180@e56g2000cwe.googlegroups.com>:
At noon, the sun and earth pull the objects on the earth's surface in
opposite directions. At midnight the sun and earth pull these objects
in same direction. Does it mean weight of the object increases at
night??
Probably we lay down at night because we are pullede harder towards the ground ;-)
Look correct to me though.
Untutored Pantelje fails to realize that the Earth and everything on it
is in free fall in the gravitation of the sun and moon, so we "feel" no
non tidal forces from those bodies.
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| User: "Jan Panteltje" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 09:00:59 AM |
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On a sunny day (Wed, 26 Apr 2006 13:58:42 GMT) it happened Sam Wormley
<swormley1@mchsi.com> wrote in <m0L3g.121946$oL.38801@attbi_s71>:
Jan Pantelje wrote:
On a sunny day (26 Apr 2006 00:15:50 -0700) it happened "Nishu"
<amitk_dni@yahoo.co.in> wrote in
<1146035750.353397.149180@e56g2000cwe.googlegroups.com>:
At noon, the sun and earth pull the objects on the earth's surface in
opposite directions. At midnight the sun and earth pull these objects
in same direction. Does it mean weight of the object increases at
night??
Probably we lay down at night because we are pullede harder towards the ground ;-)
Look correct to me though.
Untutored Pantelje fails to realize that the Earth and everything on it
is in free fall in the gravitation of the sun and moon, so we "feel" no
non tidal forces from those bodies.
Untutored? Well if you had what i had you would make more sense.
No tidal forces?
Gimme a break.
Idiot.
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| User: "Sam Wormley" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 10:06:23 AM |
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Jan Panteltje wrote:
On a sunny day (Wed, 26 Apr 2006 13:58:42 GMT) it happened Sam Wormley
<swormley1@mchsi.com> wrote in <m0L3g.121946$oL.38801@attbi_s71>:
Jan Pantelje wrote:
On a sunny day (26 Apr 2006 00:15:50 -0700) it happened "Nishu"
<amitk_dni@yahoo.co.in> wrote in
<1146035750.353397.149180@e56g2000cwe.googlegroups.com>:
At noon, the sun and earth pull the objects on the earth's surface in
opposite directions. At midnight the sun and earth pull these objects
in same direction. Does it mean weight of the object increases at
night??
Probably we lay down at night because we are pullede harder towards the ground ;-)
Look correct to me though.
Untutored Pantelje fails to realize that the Earth and everything on it
is in free fall in the gravitation of the sun and moon, so we "feel" no
non tidal forces from those bodies.
Untutored? Well if you had what i had you would make more sense.
No tidal forces?
Gimme a break.
Idiot.
What part of "non tidal forces" did you fail to comprehend?
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| User: "Jan Panteltje" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 10:17:22 AM |
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On a sunny day (Wed, 26 Apr 2006 15:06:23 GMT) it happened Sam Wormley
<swormley1@mchsi.com> wrote in <P%L3g.918707$x96.908272@attbi_s72>:
Jan Panteltje wrote:
On a sunny day (Wed, 26 Apr 2006 13:58:42 GMT) it happened Sam Wormley
<swormley1@mchsi.com> wrote in <m0L3g.121946$oL.38801@attbi_s71>:
Jan Pantelje wrote:
On a sunny day (26 Apr 2006 00:15:50 -0700) it happened "Nishu"
<amitk_dni@yahoo.co.in> wrote in
<1146035750.353397.149180@e56g2000cwe.googlegroups.com>:
At noon, the sun and earth pull the objects on the earth's surface in
opposite directions. At midnight the sun and earth pull these objects
in same direction. Does it mean weight of the object increases at
night??
Probably we lay down at night because we are pullede harder towards the ground ;-)
Look correct to me though.
Untutored Pantelje fails to realize that the Earth and everything on it
is in free fall in the gravitation of the sun and moon, so we "feel" no
non tidal forces from those bodies.
Untutored? Well if you had what i had you would make more sense.
No tidal forces?
Gimme a break.
Idiot.
What part of "non tidal forces" did you fail to comprehend?
What part of the original question did you fail to grap?
He asked 'bigger smaller', and in fizix the small differences count.
I remember years ago I said: 'A lightbeam is not affected by a magnet'.
Immediatlely I was put right......
These SMALL differences help us along, look at the gravitational field
changes in the rotating superconductor experiment at ESA.
Now are not we quiet now? hehe
It (the OP) was a very good question, and deservers a correct answer.
Not your insinuations and non-language constructs.
Y'old parrot, after all your verbatim quoting I wasa sorta hoping youde graspe
some oftit.
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| User: "Sam Wormley" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 10:25:01 AM |
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On a stormy day Jan Panteltje wrote:
What part of the original question did you fail to grap?
He asked 'bigger smaller', and in fizix the small differences count.
I remember years ago I said: 'A lightbeam is not affected by a magnet'.
Immediatlely I was put right......
These SMALL differences help us along, look at the gravitational field
changes in the rotating superconductor experiment at ESA.
Now are not we quiet now? hehe
It (the OP) was a very good question, and deservers a correct answer.
Not your insinuations and non-language constructs.
Y'old parrot, after all your verbatim quoting I wasa sorta hoping youde graspe
some oftit.
The crux of the question--do you feel your own weight while
in free fall? No you don't.
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| User: "Jan Panteltje" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 10:51:34 AM |
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On a sunny day (Wed, 26 Apr 2006 15:25:01 GMT) it happened Sam Wormley
<swormley1@mchsi.com> wrote in <hhM3g.122046$oL.8629@attbi_s71>:
On a stormy day Jan Panteltje wrote:
What part of the original question did you fail to grap?
He asked 'bigger smaller', and in fizix the small differences count.
I remember years ago I said: 'A lightbeam is not affected by a magnet'.
Immediatlely I was put right......
These SMALL differences help us along, look at the gravitational field
changes in the rotating superconductor experiment at ESA.
Now are not we quiet now? hehe
It (the OP) was a very good question, and deservers a correct answer.
Not your insinuations and non-language constructs.
Y'old parrot, after all your verbatim quoting I wasa sorta hoping youde graspe
some oftit.
The crux of the question--do you feel your own weight while
in free fall? No you don't.
He says:
'
At noon, the sun and earth pull the objects on the earth's surface in
opposite directions. At midnight the sun and earth pull these objects
in same direction. Does it mean weight of the object increases at
night??
'
So, when the object is between sun and earth (because of earth rotation,
so on the side of the earth that faces the sun, daytime), it is 'of center'
from earth gravitational center, and closer to the sun, and thus more attracted
by the sun, and thus lighter (presses less against the earth surface).
(From the frame of reference of earth, you weight it).
And vice versa.
This correct? I think so.
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| User: "FED UP" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 01:44:25 PM |
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To the original questions...yes we are heavier.
Our mass of course is unchanged.
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| User: "tadchem" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 04:45:10 PM |
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That depends on the phase of the moon. The moon has about 2.2 times
the gravitational effect on the surface of the earth as the sun.
You 'weigh' least when the sun and moon are both overhead (noon of a
new moon) and most when they are both directly underneath you (at
midnight of a new moon.)
At a full moon you weigh more at noon (the moon *under* you and the sun
overhead) than at midnight (the *sun* under you and the moon overhead).
Google "tide-raising force"
When you feel you understand this try:
http://tidesonline.nos.noaa.gov/
Tom Davidson
Richmond, VA
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| User: "" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 04:14:25 PM |
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This is a good question, and the naive answer is "no" because the earth
is in freefall, but only the center of the earth is in freefall, so
there is a solar time of day effect. Ignoring the moon, since that
wasn't part of the question, your total weight is due to the earth, the
tidal effect of the sun, and your centripital acceleration due to the
rotation of the earth.
-Bruce bbowen@pppppppacbell.nnnnnnnet
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| User: "" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 04:49:50 PM |
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This is a good question, and the naive answer is "no" because the earth
is in freefall, but only the center of the earth is in freefall, so
there is a solar time of day effect. Ignoring the moon, since that
wasn't part of the question, your total weight is due to the earth, the
tidal effect of the sun, and your centripital acceleration due to the
rotation of the earth.
-Bruce bbowen@pppppppacbell.nnnnnnnet
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| User: "" |
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| Title: Re: Are we heavier at night? |
26 Apr 2006 04:49:38 PM |
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This is a good questions, and the naive answer is "no" because the
earth is in freefall, but only the center of the earth is in freefall,
not the surface, so you're weight is a summation of the earth's force,
the tidal force of the sun, and your centripital acceleration due to
the earth's rotation. Also the moon has an effect, but it wasn't
included in the question.
-Bruce bbowen@pppppppacbell.nnnnnnnnet
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