#1
3 small ideas/queries all of which really lie on one theory. Firstly does the rotation of the earth around the sun and the centrifugal forces involved in it mean that gravity will have less effect at night than during the day. Second does the rotation of the earth mean that gravity is weaker near the equator as the centrifugal forces from the earth’s rotation will be higher and thirdly, is does the increase in centrifugal force (due to the distance from the centre of the earth’s rotation) have a effect on the gravity further out from the earth’s surface (I realise the distance from the earth’s mass directly effects the gravity further out but was wondering if this would also play a part).

Hope this all makes sense and that someone can either give me a solid reason I am wrong or prove me right. Thanks.
#3
for the 2nd question, i believe gravity gets stronger the closer you are to the center of a mass
i'm probably wrong lol i took physics 2 years ago
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#4
gravity gets weaker as you get closer to the center of the earth, till it finally becomes zero


your second assumption is true the value of gravity does change with latitude and is weaker at the equator

i don't understand your 1st and 3rd questions
Last edited by fretburn at Nov 25, 2009,
#5
yes because at the centre there will be no mass left to pull you in, this isnt necesary to my Q though. It may be Centripetal though.
#6
Quote by Tgalea
3 small ideas/queries all of which really lie on one theory. Firstly does the rotation of the earth around the sun and the centrifugal forces involved in it mean that gravity will have less effect at night than during the day. Second does the rotation of the earth mean that gravity is weaker near the equator as the centrifugal forces from the earth’s rotation will be higher and thirdly, is does the increase in centrifugal force (due to the distance from the centre of the earth’s rotation) have a effect on the gravity further out from the earth’s surface (I realise the distance from the earth’s mass directly effects the gravity further out but was wondering if this would also play a part).

Hope this all makes sense and that someone can either give me a solid reason I am wrong or prove me right. Thanks.



You're way off. Centrifugal force doesn't occur in space, which earth is also in, and therefore doesn't 'make' gravity. The generally accepted theory is that all matter with mass has gravity, therefore the greater the mass, the higher the gravity. Hence why a black hole can suck in light particles, as it has infinite mass (therefore infinite gravity) and zero volume. Btw, infinite doesn't mean 'goes on forever' in this case, it simply means it's not measurable, but it is extremely large, and vice versa with zero volume. So basically, first question no, second question no, third question no.

EDIT: to clarify, APPARENT gravity is weaker at the equator. But only infinitesimally so. But if we talk about apparent gravity in such small terms, you might as well say a pencil pulls you towards it. Maybe it exerts a slight pull. But does it really matter?

How matter HAS mass is another question which they haven't really figured out yet.
Last edited by smokin_joe at Nov 25, 2009,
#8
I wasn't suggesting it 'created' gravity, rather it simply created a force that went against gravity.
#9
In response to the second question, gravity is weaker at the equator, only due to the Earth not being completely spherical, and slightly squashed (being wider at the equator). This means that the surface is slightly further away from the centre of mass of Earth, thus experiencing a weaker gravitational pull.

Also, I don't think the 'centrifugal' force (Newton's 1st Law) has much effect on the net force experienced on Earth, as the gravitational force is a lot stronger.

Tl;dr: You're wrong.
#10
to answer everything,

it will change but the change will be too negligible to consider

(damn you got those rusty cogs in my head running again, physics class revisited)
If you want to get laid, go to college,
If you want education go to a library

-Frank Zappa-
#11
Quote by fretburn
gravity gets weaker as you get closer to the center of the earth, till it finally becomes zero


your second assumption is true the value of gravity does change with latitude and is weaker at the equator

i don't understand your 1st and 3rd questions


You couldn't be further from the truth.

The centre of the earth can be seen as a gravitational potential well. The closer you get to the centre the deeper you are in the well. The only point where the force of gravity is zero is at infinity away from it
#12
Quote by Tgalea
I wasn't suggesting it 'created' gravity, rather it simply created a force that went against gravity.



I assume you're talking about (as someone mentioned above) centripetal force? This is correct, however only in terms of classical physics (Newton's laws etc).


Here's some numbers for you.
The increase in gravity from the equator to the poles is this: 9.789 m/s^−2 to 9.832 m/s^−2. This is the 'gravity' generated by the 'centrifugal' force of the Earth spinning. In anyone's books, those are small numbers.

And also, this is not true gravity, nor is it true centrifugal/centripetal force. The requirements for both of them are not met. If you're saying that the force of the rotation of the earth has some kind of measurable effect on localized gravity, then yes you're correct. But as mentioned above, pointing it out is like saying that even if I am 10000000000000000000000000000000000000000000000000000000000000000 kilometres away from earth, it still has a gravitational pull on me. Right, but meaningless at the same time.
Last edited by smokin_joe at Nov 25, 2009,
#13
Quote by country_juggler
You couldn't be further from the truth.

The centre of the earth can be seen as a gravitational potential well. The closer you get to the centre the deeper you are in the well. The only point where the force of gravity is zero is at infinity away from it


it it? i think there is a formula to calculate the field of gravity of a given object,
hence the point of zero gravity is very definitly finite
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#14
thanks smoking_joe for a really usefull reply, I think I did mean centripetal forces too. However back to the gravity at the centre of the earth I agree with the gravity decreasing up to the point of 0 at the very centre.
#15
Quote by Tgalea
3 small ideas/queries all of which really lie on one theory. Firstly does the rotation of the earth around the sun and the centrifugal forces involved in it mean that gravity will have less effect at night than during the day. Second does the rotation of the earth mean that gravity is weaker near the equator as the centrifugal forces from the earth’s rotation will be higher and thirdly, is does the increase in centrifugal force (due to the distance from the centre of the earth’s rotation) have a effect on the gravity further out from the earth’s surface (I realise the distance from the earth’s mass directly effects the gravity further out but was wondering if this would also play a part).

Hope this all makes sense and that someone can either give me a solid reason I am wrong or prove me right. Thanks.

Gravity depends only on the Earth's mass, your mass, and your distance to its center of gravity. Centrifugal forces are insignificant.
Quote by HannibalX
it it? i think there is a formula to calculate the field of gravity of a given object,
hence the point of zero gravity is very definitly finite

Wrong, gravitational force can never equal 0.
Quote by fretburn
gravity gets weaker as you get closer to the center of the earth, till it finally becomes zero


your second assumption is true the value of gravity does change with latitude and is weaker at the equator

i don't understand your 1st and 3rd questions

No, just wrong, the closer you are to the centre of the Earth, the stronger the gravitational force becomes.
Last edited by damian_91 at Nov 25, 2009,
#16
For those saying that the force of gravity is stronger at the center of the Earth... you need to go back to your physics class.

Gravity becomes zero at the center because all of the Earth's mass is outside of your location. Therefore, it is pulling you equally in all directions. Thus, the net gravitational force on you is zero because the force vectors cancel each other out. However, it doesn't really matter, because the pressure at that depth will kill you anyway

As more information I offer the following link:
http://www.newton.dep.anl.gov/askasci/phy00/phy00646.htm
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Last edited by Prowler901 at Nov 25, 2009,
#17
Quote by Prowler901
For those saying that the force of gravity is stronger at the center of the Earth... you need to go back to your physics class.

Gravity becomes zero at the center because all of the Earth's mass is outside of your location. Therefore, it is pulling you equally in all directions. Thus, the net gravitational force on you is zero because the force vectors cancel each other out. However, it doesn't really matter, because the pressure at that depth will kill you anyway

As more information I offer the following link:
http://www.newton.dep.anl.gov/askasci/phy00/phy00646.htm

You need to go back to your physics class. Gravitational force is exerted by the CENTRE of mass, which is the centre of the earth. Since you can't occupy the same physical place as the centre of the earth, your distance to it will never be 0, but as it tends to 0, the gravitational force tends to infinite.
edit: nevermind, that's considering the Earth as a punctual object.


>.>


<.<


Last edited by damian_91 at Nov 25, 2009,
#19
somethign i heard on telly yesterday, it is believed gravity does not exist but rather something with a large mass (such as the sun) weighs down on space time creating a sort of bowl effect and is why things like the Earth revolve around it. aparently this is part of eintein's theory any nerds confirm that for me?
#20
Quote by smokin_joe
as it has infinite mass (therefore infinite gravity) and zero volume. Btw, infinite doesn't mean 'goes on forever' in this case, it simply means it's not measurable, but it is extremely large, and vice versa with zero volume. So basically, first question no, second question no, third question no.

wat?

Black holes are points of infinite density, not "infinite mass" or "zero volume"

Quote by imthehitcher
somethign i heard on telly yesterday, it is believed gravity does not exist but rather something with a large mass (such as the sun) weighs down on space time creating a sort of bowl effect and is why things like the Earth revolve around it. aparently this is part of eintein's theory any nerds confirm that for me?


That is something like Einstein's theory of why gravity is attractive, he certainly believed that gravity existed.
Last edited by Dirge Humani at Nov 25, 2009,
#21
First of Gravity exists. Einstein's theory includes a reason for why gravity may exist. He believed it was the distortion of space-time due to mass which caused gravity. This idea kind of falls down in the world of quantum though. People hypothesise the existence of gravitons which are particles which some how transfer gravitational potential.
#22
Quote by Dirge Humani
wat?

Black holes are points of infinite density, not "infinite mass" or "zero volume"



That is something like Einstein's theory of why gravity is attractive, he certainly believed that gravity existed.

sorry not that it didnt exist but that we don't know what it is.
#24
Quote by Dirge Humani
We know what it is, but not why it is.


i guess that was the point being made then
they also made the point that standing on the edge of the black hole you could see all of time or something as crazy as that
#27
Quote by evillemon
Centrifugal force doesnt exist.

|Neither does centripedal, its just the resultant of 2 other forces,



stratkat
#29
1) Gravity has the same effect at night
2) Now if the Earth was a sphere then it's gravity would maintain the same at all points. However due only to the fact that it bulges around the equator the gravity is marginally less (and i do mean marginally, it'd be a tiny fraction of a difference)
3) I dont understand

and gravity is obviously largest at the centre of the Earth, how could you even imagine otherwise :S. Putting it in the simplest way possible, if gravity increases the further away from the object and is seen to be exerted from the centre of mass then it's obvious that the closer you are to the centre more powerful gravity is. Well when i say powerful, gravity is one of the weakest forces we know of, but still, you get my drift.
#30
Okay, lets start out with this, gravity is the attraction of 2 objects with mass, therefor, it there are even 2 single atoms, gravity will always be present, center of the earth or not.

^That is right, in the center of the earth, you are being pulled from all directions.
And how could someone even think that gravity had a different effect at night?

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#31
As far as I know, the earth's gravity is dependant on how fast it is rotating and not much else. The only exceptions to this that I could see would be on the north and south pole's of the planet for the reason that everything is spinning on them instead of around them. That's just me though. I only took one year of any kind of physics.
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#33
Quote by Sewn Up
As far as I know, the earth's gravity is dependant on how fast it is rotating and not much else. The only exceptions to this that I could see would be on the north and south pole's of the planet for the reason that everything is spinning on them instead of around them. That's just me though. I only took one year of any kind of physics.


Gravity is dependant on mass and not much else. =/ Otherwise as you say there would be no gravity at the axical north and south pole. Gravity is simple the attraction of any object with mass. You are attracted by gravity to the screen you are reading it on and it is attracted to you. However because the mass of the screen and of you is so little it has an insignificant effect.
#34
....howwould it have a large mass to start with if gravity didnt exist. Also, back to my initial points about gravity from day to night and from equator to the north pole, I spent a bit of my physics lesson this week calculating the forces that would act. I dont have the exact numbers on me now but I remember a few examples I calculated using my friends mass of 90kg. From day to night I calculated that his mass would change by 1.8 grams, I agree that this is rather insignificant indeed but more interesting is the change in mass between the equator and the poles (considering only centripetal forces) which was calculated to 300g.
#35
Quote by Tgalea
3 small ideas/queries all of which really lie on one theory. Firstly does the rotation of the earth around the sun and the centrifugal forces involved in it mean that gravity will have less effect at night than during the day. Second does the rotation of the earth mean that gravity is weaker near the equator as the centrifugal forces from the earth’s rotation will be higher and thirdly, is does the increase in centrifugal force (due to the distance from the centre of the earth’s rotation) have a effect on the gravity further out from the earth’s surface (I realise the distance from the earth’s mass directly effects the gravity further out but was wondering if this would also play a part).

Hope this all makes sense and that someone can either give me a solid reason I am wrong or prove me right. Thanks.


I don't think gravity has less effect in night, you still have Earth's gravitational forces. I don't think the equator has weaker gravitational forces, the center of the Earth is what holds this all together, and every spot of Earth, including the equator, is the same distance from the core. And to the third, I think it does. Sorry for my stupidity, I just thought I might be able to get this right, but I'm not going to.
#36
and i'm not suggesting that gravity changes from day to night just the centripetal force of the earths rotation round the sun either adds force in the direction of gravity (mid day) or works against it (midnight) changing the RESULTANT force.
#37
Centripetal. OP is irrelevant.
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#38
Well think of it this way. Here are the two gravitational forces during the day:

<--- Sun's gravity
Earth's gravity --->

And at night:

<---Sun's Gravity
<---Earth's Gravity

Sooooo...

But there isn't really a measurable difference and it's a bad question if it's meant to test your understanding of net forces.

And yes gravity is weaker near the equator since the earth is slightly bulged there. Since the gravitational force is GMm/r^2 a bigger r results in a smaller force.