Is it true that Earth's gravity is less at the equator?

  • 27 Replies
  • 8883 Views

0 Members and 1 Guest are viewing this topic.

*

Offline common_sense_seeker

  • Sr. Member
  • ****
  • 213
    • View Profile
    • Believers In Gravity Shielding (BiGS)
Is it not counter-intuitive to think that the Earth bulges at the equator due to it's rotation, yet the surface gravity (0.99732g) is less than if you were at the poles? Surely the fact that there is more mass between an object at the equator and the center of the Earth should be a factor in the explanation? But there is no mention of this in the textbook reason, which is not very convincing in my opinion. Does anyone agree that this is highly counter-intuitive?
« Last Edit: 03/10/2008 12:08:56 by chris »

*

Offline rosy

  • Neilep Level Member
  • ******
  • 1018
  • Chemistry
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #1 on: 30/09/2008 11:33:44 »
Nope, makes perfect sense. Will try to find a diagram that explains it nicely when I get a minute.

*

Offline Bored chemist

  • Neilep Level Member
  • ******
  • 8739
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #2 on: 30/09/2008 19:24:22 »
CSS,
You must think it's really counter intuitive. You have posted at least 3 times about it.
Actually it makes perfect sense, but you don't understand it.
Please disregard all previous signatures.

*

lyner

  • Guest
Re: Is it true that Earth's gravity is less at the equator?
« Reply #3 on: 30/09/2008 21:27:00 »
Intuition is a really bad basis for Science, in any case. Work it out properly and it gives you the right answer. What more could you ask?

*

Offline LeeE

  • Neilep Level Member
  • ******
  • 3382
    • View Profile
    • Spatial
Re: Is it true that Earth's gravity is less at the equator?
« Reply #4 on: 30/09/2008 21:30:40 »
Groan...........
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

*

blakestyger

  • Guest
Re: Is it true that Earth's gravity is less at the equator?
« Reply #5 on: 30/09/2008 23:33:36 »
CSS - Gravity calculation involves mass and distance.

*

lyner

  • Guest
Re: Is it true that Earth's gravity is less at the equator?
« Reply #6 on: 01/10/2008 00:25:09 »
Quote
CSS: But there is no mention of this in the textbook reason,

And which textbook have you been reading?
I wonder whether you have actually read a serious textbook or if you would have understood what it said. Any graduate level book will explain the matter perfectly adequately - you may need to be able to follow the integration, though.

*

Offline Bored chemist

  • Neilep Level Member
  • ******
  • 8739
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #7 on: 01/10/2008 06:54:42 »
I think this is more "school playground" level than graduate level. Most kids understand that a merry go round throws you off because it spins. It seems css has failed to understand this (or he's a troll).
Please disregard all previous signatures.

*

Offline turnipsock

  • Hero Member
  • *****
  • 586
  • Beekeeper to the unsuspecting
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #8 on: 01/10/2008 11:00:00 »
where are the sun and moon in this?
Beeswax: Natures petrol tank sealant.

When things are in 3D, is it always the same three dimensions?

*

Offline common_sense_seeker

  • Sr. Member
  • ****
  • 213
    • View Profile
    • Believers In Gravity Shielding (BiGS)
Re: Is it true that Earth's gravity is less at the equator?
« Reply #9 on: 01/10/2008 13:36:09 »
Jeez, I willing to admit I've made a mistake if need be. I'll take a proper look at the standard solution in my own time. Just thinking out loud, that's all.

*

Offline Don_1

  • Neilep Level Member
  • ******
  • 6890
  • A stupid comment for every occasion.
    • View Profile
    • Knight Light Haulage
Re: Is it true that Earth's gravity is less at the equator?
« Reply #10 on: 01/10/2008 14:27:21 »
Would centrifugal force play a part in this?
If brains were made of dynamite, I wouldn't have enough to blow my nose.

*

Offline common_sense_seeker

  • Sr. Member
  • ****
  • 213
    • View Profile
    • Believers In Gravity Shielding (BiGS)
Re: Is it true that Earth's gravity is less at the equator?
« Reply #11 on: 01/10/2008 16:23:39 »
I think this is more "school playground" level than graduate level. Most kids understand that a merry go round throws you off because it spins. It seems css has failed to understand this (or he's a troll).

It's not as clear cut as may think. The Moon isn't spinning about it's own axis in the same way that the Earth is. But it still has gravitational anomalies that aren't easy to explain. It also has flattening, and has a lower average equatorial surface gravity. Therefore it can't be due to centrifugal force.

If the Earth stopped spinning, would it suddenly change to more surface gravity at the equator, due to the loss of centrifugal force?
« Last Edit: 01/10/2008 16:39:41 by common_sense_seeker »

*

Offline common_sense_seeker

  • Sr. Member
  • ****
  • 213
    • View Profile
    • Believers In Gravity Shielding (BiGS)
Re: Is it true that Earth's gravity is less at the equator?
« Reply #12 on: 01/10/2008 16:45:00 »
The standard argument would suggest that it would due to loss of centrifugal force. Would surface gravity then be greater at the equator than at the poles? The Moon isn't spinning though and this still has a lower surface gravity, suggesting that this may be the case for the Earth as well. Could the answer be due to irregularities of the gravitational field of the core, which are fixed?
« Last Edit: 01/10/2008 16:48:48 by common_sense_seeker »

*

Offline BenV

  • Neilep Level Member
  • ******
  • 1503
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #13 on: 01/10/2008 17:18:44 »
CSS - please don't start new topics to discuss subjects already under discussion in existing threads.  I've merged this one into the existing one.

Oh, and you've shown that you're not reading anyone's posts by yet again claiming that the moon doesn't spin.  The moon spins once per month, hence why it's always the same face towards us.  Place an apple on a table - orbit around that apple making sure you're facing it all the time - have you rotated - of course you have! 360 degrees!

People will be hard pushed to take you seriously when you repeatedly make very simple errors like that.
« Last Edit: 01/10/2008 17:24:40 by BenV »

*

Offline Bored chemist

  • Neilep Level Member
  • ******
  • 8739
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #14 on: 01/10/2008 20:13:48 »
"The Moon isn't spinning about it's own axis in the same way that the Earth is."
What, exactly, will it take to get it into your thick head that the moon is spinning?

"Jeez, I willing to admit I've made a mistake if need be. "
No, you are quite clearly not because you repeat the mistake, even after it has been pointed out to you.


"If the Earth stopped spinning, would it suddenly change to more surface gravity at the equator, due to the loss of centrifugal force?"
Yes; got a problem with that?

Of course there would be what politicians would decribe as "a period of adjustment" where everything came to a screeching halt from up to about a thousand miles an hour.
Please disregard all previous signatures.

*

Offline niall

  • Jr. Member
  • **
  • 10
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #15 on: 01/10/2008 23:07:59 »
OK, so, back to the point  [;)]

Its all very well saying "go and do the integration" but not everyone can do it and its only one way of "explaining" it. I think the main issue you are having, css, is that
Quote
there is more mass between an object at the equator and the center of the Earth
. I'm not sure, but, the Earth's rotation causes the bulging round the middle of the Earth. This means that its stretched and there is not more mass as the Earth is less dense. There is exactly the same mass as anywhere else on the Earth's surface but you are further away from the middle so the field is less.

*

Offline turnipsock

  • Hero Member
  • *****
  • 586
  • Beekeeper to the unsuspecting
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #16 on: 01/10/2008 23:25:52 »
The moon has stopped 'spinning' in relation to the earth. The Earth will eventually stop spinning in relation to the sun. The earths spinning is going to be further slowed by all these wind farms and tidal energy things, is our PM unaware of Newton's laws?
Beeswax: Natures petrol tank sealant.

When things are in 3D, is it always the same three dimensions?

*

Offline common_sense_seeker

  • Sr. Member
  • ****
  • 213
    • View Profile
    • Believers In Gravity Shielding (BiGS)
Re: Is it true that Earth's gravity is less at the equator?
« Reply #17 on: 02/10/2008 10:22:11 »
OK, so, back to the point  [;)]

Its all very well saying "go and do the integration" but not everyone can do it and its only one way of "explaining" it. I think the main issue you are having, css, is that
Quote
there is more mass between an object at the equator and the center of the Earth
. I'm not sure, but, the Earth's rotation causes the bulging round the middle of the Earth. This means that its stretched and there is not more mass as the Earth is less dense. There is exactly the same mass as anywhere else on the Earth's surface but you are further away from the middle so the field is less.

Good point. Only less dense matter at the equatorial bulge could explain it. I'm dubious about this though. I think centrifugal force would tend to make less dense material migrate away from the equator, like bubbles in a washing machine on spin mode.

*

lyner

  • Guest
Re: Is it true that Earth's gravity is less at the equator?
« Reply #18 on: 02/10/2008 15:43:55 »
neill - that is a fair comment about not everone being able to do the integration. BUT, if you're going to challenge the existing theory you have to have some basis. Anyone who can't do the integration is not really in a position to challenge its results.
Most of this stuff is not a matter of opinion. The results at cutting edge of Science are open to opinion but 'informed' opinion is the only opinion which is worth anything. Some of the views you can read in these forums are incredibly arrogant; they discount, at a stroke, all the seriously good work which has been done 'at the coal face' by people with wisdom, knowledge and skills. None of these seem to be part of css's repertoire.

To prove my point, look at his last post. The bubbles (less dense) in a washing machine are actually forced into the middle and the water (the more dense) goes to the outside. His comment is just nonsense. (Has he ever actually been in a spinning washing machine to see?)
If you want a really graphic demonstration of this effect, take a helium-filled party balloon on a string into a car. When the car goes round a corner the balloon will lean INTO the bend for the same reason.

*

Offline Bored chemist

  • Neilep Level Member
  • ******
  • 8739
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #19 on: 02/10/2008 19:00:59 »
OK css. The next mistake you have made and repeated (but claim to be willing to accept) is not to realise that the mass of the earth is exactly the same wherever you are.
So, to say the mass is more when you are at the equator is simply wrong. The whole thread doesn't make sense because the title is nonsense.
Also, as has been pointed out before, at the equator you are further away from most of that mass, so it has less efect and that reduces the net effect of gravity .
Again, as has also been pointed out, any child in the playground will tell you that things that are spinning tend to throw you off.
I don't understand how you could have been unaware of this (even before it was pointed out) but since you have now been told about it why don't you accept it?

The obvious conclusion is that you are either very stupid, trolling, or both.
« Last Edit: 02/10/2008 19:03:27 by Bored chemist »
Please disregard all previous signatures.

*

Offline RD

  • Neilep Level Member
  • ******
  • 8171
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #20 on: 02/10/2008 19:11:55 »
Just a thought...

As the Earth is mostly fluid, (only the crust and inner core are solid), wouldn't the equatorial bulge disappear if the earth stopped rotating ?, i.e. wouldn't the earth change from an oblate spheroid to a sphere without the centrifugal force caused by rotation ?.

*

Offline niall

  • Jr. Member
  • **
  • 10
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #21 on: 02/10/2008 21:41:42 »
That's exactly what I was trying to say RD! That's my point - and because of this the Earth is less dense below your feet at the equator so you can have more distance between you and the middle of the Earth but the same mass so less graviatational pull. As everyone else has pointed out there is also a centrafugal force that acts against the gravity. These two add up to less gravity at the equator, surely, end of discussion...

Sorry sophiecentaur, I didn't realise we were allowed to smack css down so hard - I was trying to be diplomatic! He's obviously got some of you pretty riled and it sound like this question has been posted before and the answer disputed?

*

Offline common_sense_seeker

  • Sr. Member
  • ****
  • 213
    • View Profile
    • Believers In Gravity Shielding (BiGS)
Re: Is it true that Earth's gravity is less at the equator?
« Reply #22 on: 02/10/2008 22:38:12 »
I'm bored to the core myself. I'll leave you all to your laughable tittle-tattle and publish a scientific paper instead. Bye. It's been fun.

*

lyner

  • Guest
Re: Is it true that Earth's gravity is less at the equator?
« Reply #23 on: 02/10/2008 23:42:22 »
niall
Enough's enough at times and css keeps coming back for more. I would never start off so hard with someone who is merely 'misguided'.

I am not sure where you're going with the idea about density being lower near the equator. Are you suggesting this is because of centrifugal force, pressure or what?
I have been trying to relate this to the possible differences in 'depth' of the Oceans over the Earth's surface.

c.s.s.
I look forward to the 'Scientific Paper'. If it were kept to the length of a short paragraph, it could find a place in the Beano, possibly.

*

Offline LeeE

  • Neilep Level Member
  • ******
  • 3382
    • View Profile
    • Spatial
Re: Is it true that Earth's gravity is less at the equator?
« Reply #24 on: 03/10/2008 00:38:12 »
I'm bored to the core myself. I'll leave you all to your laughable tittle-tattle and publish a scientific paper instead. Bye. It's been fun.

Goodbye.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

*

Offline Bored chemist

  • Neilep Level Member
  • ******
  • 8739
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #25 on: 03/10/2008 07:05:54 »
I'm bored to the core myself. I'll leave you all to your laughable tittle-tattle and publish a scientific paper instead. Bye. It's been fun.
My guess is that that post will be wrong on all 4 counts.
Please disregard all previous signatures.

*

Offline niall

  • Jr. Member
  • **
  • 10
    • View Profile
Re: Is it true that Earth's gravity is less at the equator?
« Reply #26 on: 03/10/2008 11:06:59 »
OK - sure, centrafugal force is greater at the equator and this acts in the opposite direction to weight (centrafugal not centrapetal, right?) I totally accept that. One anal point I would make is that this (technically) doesn't affect the gravitational force - the gravity is still there its just the cetrafugal force acts in the opposite direction i.e. you weigh less.
But the spin of the Earth will make it squat because of this, like spinning a balloon full of water. The gravitational pull of the sun and moon distort the shape of the Earth and give actual solid ground tides of ~20cm. So what I'm saying is that the Earth is a lot more pliable than we think...
Just had a thought. If you spin a water balloon it isn't less dense at the "equator" is it. It just squashes down and redistributes its mass...hmm curios. I guess I didn't have it quite right before. It may be less dense at the equator but probably not. But (as I think a lot of you have said, just differently...
If you shrank the Earth  down to the size of a football, keeping the same mass, and then stood in space where the old equator used to be and where the old north pole used to be, you'd be closer to the foorball at the north pole so gravity would be greater.

*

lyner

  • Guest
Is it true that Earth's gravity is less at the equator?
« Reply #27 on: 03/10/2008 18:02:39 »
Given a few hundred million years and a steady force acting on it, even the stiff old Lithosphere will move eventually. The stuff underneath behaves like a liquid - convection currents are constantly sloshing material around.
The present shape is the 'equilibrium condition' with the gravitational  imbalance being equal to the rotational force. It shouldn't be too hard to work it out - if I could be **sed.