Gravity on a flat Earth.

So,
Indeed you can determine g at a certain point with observation and fixed gravity g= 9.8 ms2, but it also tells you the distance to the earth's center from that point.
It gives us the radius of the earth, your observation matches the radius of the Earth!
Because at the surface 9.8 ms2 matches exactly the Earth radius of 6.371 km

The mass of the Earth, and the radius of the earth  squared in relation with the the acceleration of gravity proofs the Earth is in fact a sphere!

Thank you.

If you want to play smart get your facts straight. The mass of the earth was calculated using this gravitational formula, not vice versa! (There was no scale big enough, unfortunately...)

Yeah he's been told that numerous times.

I'm betting he's gonna go the same way as physics teacher did.

There are people here on this thread disguised as "round earthy" don't want to call names but....kami 
Kami you used in your first reply the "standard gravity factor and this is based on 9.8ms2 !!!
You used a calculation from a internet calculator that inprent this factor, o man this is getting ridiculous.
(an alternate unit is the g per second), nobody was responding to this so i knew from this point i am dealing with impostors, so called roundies from the flat earth society

Like i said, g= is not constant meaning it depends on your distance to the Earth's center and the mass of bigM.
The Earth is a sphere, the earth is not flat and certainly not an infinite plain to make your crazy idea of UV possible.
I have a very busy day, but kami and boys serieus i was very cautious with your first reply to me, because i have a very big hart.

But i think i'm gonna play it differently,
I will post my last command later on.

 

"Agreed your original question has been answered Bal, perhaps you would like to start another thread with another argument.

you know all the posters arguing with you on this are RE right?

Why spoil it."

-What?
Please kid go do your homework.

Missed this.

Ohh Noes!!1!!1!!33!!

I was called a kid on teh internets, whatever shall I do now.

Guys?

Seriously tho messing with Kami on maths your gonna get burned.

He clearly didnt assume a 9.8m/s2 g, thats why he came to a different number than 9.8m/s2. Not sure where you got that from.

Did you take physics in highschool?

The mass of the earth was calculated using this gravitational formula, not vice versa! (There was no scale big enough, unfortunately...)

Read it.

You lost, try again.

Dumbshoe.

"If you want to play smart get your facts straight. The mass of the earth was calculated using this gravitational formula"



-Wrong use Kepler's law.
Mearth= 4pi2a3: T2G
4 times pi squared times the half-axis of the elliptical orbit cubed = the orbital period squared times the gravitational constant. ( oops i forgot something in the equation, i bet you can't see what it is )
keeps getting crazier...
Have patience, tonight i have enough time and i will show you how wrong you are Kami, round earthy

For now, let's start with the beginning first.
s=v*t
You used the unit g/s a standard gravity factor for calculating the acceleration.
Your online calculator tool has the factor 9.8ms2 !! built in, you guys don't know what i meant with my reply (alternate unit is the g/s

But enough for know i will come later with my last reply...
Disputeone.
Parroting kami isn't making your claims better, just stand by and let kami and i do the talking ok.   

The mass of the earth could also have been calculated by the moons orbital period. I'm not sure if OT was, but that's how they calculate the mass of the gas giants.

"The mass of the earth could also have been calculated by the moons orbital period. I'm not sure if OT was, but that's how they calculate the mass of the gas giants."

-Yes , we can calculate the mass of the Earth using the Moon's orbit in kepler's laws.
T2= 4Pi2 divided by G(M+m)*a3.

This formula is directly derived from newton's formula of gravitational attraction.

The only thing i typed in my "online calculator tool" was 20/2.5^2, the rest was done with paper and pen; no preprogrammed 9.81m/s^2. You might notice, as disputeone already mentioned, that i came to a completely different value on g, based on your premises.

But okay, enlighten me. Calculate the mass of the Earth without using Newton's formula of gravitational attraction.
Of course, you are free to use the original kepler laws
(1. planets move in conic sections, 2. A line joining a planet and the Sun sweeps out equal areas during equal intervals of time, 3. The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.)

The formula correlating the orbital period to masses is derived from Newton's formula though, so you can not use that one.

Feel free to call names and show me wrong. Best start with this calculation

I'm no expert, but there is probably a way to derive Kepler's third law without universal gravitation.

If you observe then going in elliptical paths, you immediately known that the centripetal acceleration gets weaker with distance etc.

I'm no expert, but there is probably a way to derive Kepler's third law without universal gravitation.

If you observe then going in elliptical paths, you immediately known that the centripetal acceleration gets weaker with distance etc.

That is true, kepler did that. But he did (and could) not correlate those paths to the masses of the planets in any ways, he just figured that the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit (which is his third law).

"If you want to play smart get your facts straight. The mass of the earth was calculated using this gravitational formula"

Sorry to be throwing spanners around and getting them stuck in the works, but, look at the time-line:

Kepler's work (published between 1609 and 1619) improved the heliocentric theory of Nicolaus Copernicus, explaining how the planets' speeds varied, and using elliptical orbits rather than circular orbits with epicycles.

And

Isaac Newton showed in 1687 that relationships like Kepler's would apply in the Solar System to a good approximation, as a consequence of his own laws of motion and law of universal gravitation.

Both from Kepler's laws of planetary motion.
But, at this time "G", the Universal Gravitational Constant was not known, not even approximately.

Were the size of the earth and it's density known, the mass could be easily calculated, but!
The size of the earth was known to Newton, but the density of the earth was not, so he estimated (guessed) that it might be about the same as the surface rocks - roughly 2,900 kg/m³, but he was quite wrong.

In the following "g" is the acceleration due to gravity on the earth's surface, at a radius "R" and "G" is the Universal Gravitational Constant.

It was not till Henry Cavendish came along in 1797-1798 with the intention of measuring the density (specific gravity) of the earth, and hence it's mass. The "Gravitational Constant" never appears in Cavendish's work, though "G" can readily be found from his work.
So "G" was not known for over a century after Newton''s work. The historical order of these values would be:

• The value of "g" by Galileo, though greatly refined by Robert Hooke, Isaac Newton and others.
  
  
• Kepler's laws of planetary motion.
  
  
• Newton's Law of Universal Gravitation F = G x m x M/R², but "G" was not yet known, though G x M was.
  
  
• Cavendish, in 1797-98, "measured" the density of the earth and hence "M" and "G" could finally be determined.
  

Certainly, historically then, "The mass of the earth was calculated using this gravitational formula"

Eratosthenes calculated the earth circumference and thus the radius, somewhere 200 BC.
With the Earth circumference and known density we can easily figure out the Earth's mass, without the gravitational acceleration and gravitational constant!
My point is, the Earth's radius is  6,371 km, proven by the flat Earth itself by pointing out g=9.8ms2 at the surface. Lol
Or are you assuming Eratosthenes was wrong too?
Can you explain why?

We don't have to explain Kepler here, i could no problem.
But this makes things a little easier.

And i could calculate the Earth's mass with Erathosthenes findings
Strange all these equations point out the Earth is a sphere...really strange.

Well back to work sorry bothering you.

Kami

Maybe you could answer my question, what's wrong with my equation?
I made mistake on purpose there can you point it out please?
Hard putting them in a online calculater isn't it

Kami

Maybe you could answer my question, what's wrong with my equation?
I made mistake on purpose there can you point it out please?
Hard putting them in a online calculater isn't it

Which equation do you mean?

Then, by all means, tell me how I can measure the density of the earth. I have no problems with Eratosthenes' work, but I am fairly certain that the (average) density of the earth was derived from its measured mass, not vice versa.

V=4/3 *Pi r3 , and we know 1 m3 Earth rock weights approximately 5000 kg.
Put a big piece of rock (1m3) on a scale, with this number we can determine roughly the Earth's mass

We know the volume, we know the radius and we can weigh a m3 of rock !
Calculate with a m3 of rock and you will see you that you are close determining the Earth's mass without g and G.

Kami,

"Mearth= 4pi2a3: T2G
4 times pi squared times the half-axis of the elliptical orbit cubed = the orbital period squared times the gravitational constant. ( oops i forgot something in the equation, i bet you can't see what it is )"

Kami,

The flat earth society has no theory, it's a believe.
Everything points in the direction of a round beautiful blue dot.
It's not a manner of perception, Mathematics proves the earth is a sphere.

Even without knowing the Earth's mass, we know the Earth is a sphere, because of Eratosthenes.
Why are you doing this, are you agnostic wtf!

I leave it be.

Kami,

The flat earth society has no theory, it's a believe.
Everything points in the direction of a round beautiful blue dot.
It's not a manner of perception, Mathematics proves the earth is a sphere.

Even without knowing the Earth's mass, we know the Earth is a sphere, because of Eratosthenes.
Why are you doing this, are you agnostic wtf!

I leave it be.

I agree with you there, whole-heartedly. But just because you believe in a round earth does not mean that you are free from error.

Kami,

"Mearth= 4pi2a3: T2G
4 times pi squared times the half-axis of the elliptical orbit cubed = the orbital period squared times the gravitational constant. ( oops i forgot something in the equation, i bet you can't see what it is )"

The upper one is correct (i suppose), considering you assume a nearly circular orbit and the mass of the satellite to be neglible compared to earth's mass. In the lower one you forgot the "Mearth". And yes, this is exactly what one can find by simple googling without putting an effort into this.

V=4/3 *Pi r3 , and we know 1 m3 Earth rock weights approximately 5000 kg.
Put a big piece of rock (1m3) on a scale, with this number we can determine roughly the Earth's mass

We know the volume, we know the radius and we can weigh a m3 of rock !
Calculate with a m3 of rock and you will see you that you are close determining the Earth's mass without g and G.

It is just that the earth is much denser at the core than on the surface and that the density of earth rock is approximately 2.9t/m^3, not 5 (compare rabinoz' post). If you take some surface layer and propose that its density is roughly equal to earth's without knowing a single thing about the interior, then you might have an approximation that is correct by order of magnitude, but nothing more. To get a good estimate of earth's mass you need to analyze its gravitational field OR somehow measure its density (i dont know much about this but i think it could be possible to do this by analyzing seismic waves or something similar; this is just a guess though and those methods are quite recent, the mass of the earth has been known by then).

Dunning- kruger.

Oh my, the irony is so strong it burns.

Quote from: BalGehakt on November 01, 2016, 04:44:18 AM

Kami

Maybe you could answer my question, what's wrong with my equation?
I made mistake on purpose there can you point it out please?
Hard putting them in a online calculater isn't it

Which equation do you mean?

Then, by all means, tell me how I can measure the density of the earth. I have no problems with Eratosthenes' work, but I am fairly certain that the (average) density of the earth was derived from its measured mass, not vice versa.

The density and mass were found more or less together in 1797-98 by Henry Carpenter - look him up in Wikipedia.
The Universal Gravitational Constant could then be calculated from that mass.

The density and mass were found more or less together in 1797-98 by Henry Carpenter - look him up in Wikipedia.
The Universal Gravitational Constant could then be calculated from that mass.

That is interesting, although I can't seem to find him.. could you provide a link?

Kami,

Kami said,
"In the lower one you forgot the Mass of the earth"


My equations,
-Upper one,
Mearth= 4pi2a3: T2G
4 times pi squared times the half-axis of the elliptical orbit cubed = the orbital period squared times the gravitational constant. ( oops i forgot something in the equation, i bet you can't see what it is )

Lower one i said,
T2= 4Pi2 divided by G(M+m)*a3
The Big M stands for the mass of the earth.Thus the correct equation..
The first one i gave is incorrect, can you see it?
You don't have to answer this.I really don't mind, this from my textbooks, i don't think you are able simple Google it

On topic,
Round Earth is also just a believe? Explain please why you think that.

And,
"You cant calculate the mass of the Earth exactly without g, only roughly with a m3 rock"

Let's use your analogy,
My first question was, how did the flat Earth community came up with this figure 9.8ms2?
Just by observing....and we know we can neglect the changing of g over a SHORT distance.
So s=v*t is sufficient, you say.
Wrong!

Roughly 9.8ms2, because you can neglect short distances like 100 meters above the surface.
But with rocket science you cant neglect even minimal change in g.
I want to measure a falling object from 2000 m to the ground.
Do you need to know the distance to the earth's center or not, roughly isn't enough.
No you can't, only roughly without the distance to the center of the Earth squared......, again if you want to be sure, you need to know the object's distance to the Earth squared!

g=9.8ms2 at the Earth's surface is like saying the Earth is round.
With simple geometry you can calculate the Earth circumference, this is math and proof the Earth is a beautiful round ball.
Why is this just belief the Earth is round, kami?

Sorry for the rough text.
Don't have a lot of time ....

Logic dictates that the earth would be denser than rock, since denser items would sink to the middle.

Kami,

Kami said,
"In the lower one you forgot the Mass of the earth"


My equations,
-Upper one,
Mearth= 4pi2a3: T2G
4 times pi squared times the half-axis of the elliptical orbit cubed = the orbital period squared times the gravitational constant. ( oops i forgot something in the equation, i bet you can't see what it is )

Lower one i said,
T2= 4Pi2 divided by G(M+m)*a3
The Big M stands for the mass of the earth.Thus the correct equation..
The first one i gave is incorrect, can you see it?
You don't have to answer this.I really don't mind, this from my textbooks, i don't think you are able simple Google it

Did not see the second equation. The m there stands for the mass of the second object; as I said, if this is neglible (so M+m roughly equals M), then the upper one is correct.

On topic,
Round Earth is also just a believe? Explain please why you think that.

Let us not argue about words. Certainly the earth appears to be a globe and all evidence points to it, but you can not rule out that we all live in a matrix constructed by our alien overlords making us believe that the earth is round. Not saying this is true, but you can not know anything for sure in physics, there are just assumptions that were verified to such a high degree of certainty that we believe them to be true (for example we believe that wenn you jump, you fall down. This has happened every time. But it could be that when you jump next time, you will fly into space and die. Granted, the possibility is very, very small, but not entirely zero).

Let me make that clear: I am not arguing against a globe earth.

And,
"You cant calculate the mass of the Earth exactly without g, only roughly with a m3 rock"

Let's use your analogy,
My first question was, how did the flat Earth community came up with this figure 9.8ms2?
Just by observing....and we know we can neglect the changing of g over a SHORT distance.
So s=v*t is sufficient, you say.
Wrong!

Roughly 9.8ms2, because you can neglect short distances like 100 meters above the surface.
But with rocket science you cant neglect even minimal change in g.
I want to measure a falling object from 2000 m to the ground.
Do you need to know the distance to the earth's center or not, roughly isn't enough.
No you can't, only roughly without the distance to the center of the Earth squared......, again if you want to be sure, you need to know the object's distance to the Earth squared!

g=9.8ms2 at the Earth's surface is like saying the Earth is round.
With simple geometry you can calculate the Earth circumference, this is math and proof the Earth is a beautiful round ball.
Why is this just belief the Earth is round, kami?

Sorry for the rough text.
Don't have a lot of time ....

Your first question was answered correctly. Certainly, when you go into rocket science F=m*g will not suffice anymore, but for all surface-based observations (and even airplanes) this suffices. The inaccuracies due to varying g over the first 10 kilometers are 0.3%. That is really small compared to other possible errors like air resistance and minor things like a not exactly timed clock, a slightly incorrectly measured height, etc.

As no flat-earther has ever done rocket science (and some believe rockets do not work in vacuum), we can safely say that a flat earther could calculate the value g=9.81m/s^2 with a simple, repeatable experiment.

"Your first question was answered correctly."

-True, if you are a flat earth believer or a round earth agnostic :p
By observation over a short distance we can measure the gravitational acceleration to be 9.8ms2, i agree!
But Don't you want to know why it falls ?
Because your observation only tells you how fast it falls and tells you the acceleration over this short distance, but not why it falls.
Also if you do your observation all around the world you will see the acceleration at the earth's surface varies between 9.789 ms2 and 9.822 ms2, The biggest difference in the force of gravity NEAR THE EARTHS surface is caused by the centrifugal (centrifugal) force, which cancels out the force of gravity for a small part.

g= not uniform( the gravitational field around the Earth is not a constant and g depends on the distance of the object to the Earth's center, the Earth is not an infinite plain and the light of the Sun takes 8 minuten to reach our surface of the Earth, do you agree with these facts so far?

I have to be more specific i guess.

My main concern is this, you said "we never put the Earth on a scale".
This tells me you are trying to somehow push all scientific work done in history and modern science today is based on wrong "assumptions". (i meant wrong mathematical equations).

I want to know where did it go wrong in history.
Because if you don't agree with g=G*Mearth/r2 i think it's reasonable to ask why.
I have learned that g comes from the earth center the mass that warpes space-time, and everyone else in modern science as well.

-How does gravity work according to you?

-We had a discussion my brother and i, about the scientific work done by Ligo, and the discovery they made in 2015.
Physically detecting gravitational waves, generated by black holes.
What's your opinion on this discovery?

-The matrix analogy....
Hmmm, yes nice science fiction story, don't want to go deeper in this analogy if you don't mind.

More questions later.

Ok lbye bye

" Certainly the earth appears to be a globe and all evidence points to it, but you can not rule out that we all live in a matrix constructed by our alien overlords making us believe that the earth is round."

-Yep your agnostic.
Joure smart and resourceful, the answer is not hidden.
It would be easy for you to know the Earth is round, i want to know why doubt?
What sort of knowledge do you posses that i don't have to be agnostic about the shape of the Earth

Shit i just said i don't want to go deeper in this analogy.....

"because there was no scale big enough unfortunately"

-This is not science, it's woowoo
I don't know what to say, it doesn't make sense to me.
Math and physics proved g=G*Mearth/r2.
Eratosthenes method is even enough to determine the Earth's circumference and thus proving the Earth is round.

What am i doing wrong?

Disputeone


"Yeah he's been told that numerous times.

I'm betting he's gonna go the same way as physics teacher did." And that makes you chuckle right 


No, i'm quitte tough.
And I practice my English.
And i like talking to people,btw i acknowledge my lack of mutual understanding, but i think this is not all my fault!

But Don't you want to know why it falls ?

I do! But to be fair, while the bending of spacetime does explain gravity, why do masses bend spacetime?
For every answered question a new, unanswered one will appear

g= not uniform( the gravitational field around the Earth is not a constant and g depends on the distance of the object to the Earth's center, the Earth is not an infinite plain and the light of the Sun takes 8 minuten to reach our surface of the Earth, do you agree with these facts so far?

Yes.

My main concern is this, you said "we never put the Earth on a scale".
This tells me you are trying to somehow push all scientific work done in history and modern science today is based on wrong assumptions.

I am just saying that the statement "we derived g from G and M" is wrong, the scale was just a joke

I want to know which wrong assumptions in history.
Because if you don't agree with g=G*Mearth/r2 i think it's reasonable to ask why.
I have learned that g comes from the earth center the mass that warpes space-time, and everyone else in modern science as well.

I am a huge fan of general relativity, which contradicts this assumption on large scales. Otherwise, I agree with you

-We had a discussion my brother and i, about the scientific work done by Ligo, and the discovery they made in 2015.
Physically detecting gravitational waves, generated by black holes.
What's your opinion on this discovery?

It is awesome, though not as awesome as the media put it. Gravitational waves have been proven for several years now, they have just been directly detected the first time. Most newspapers seem to confuse this.

-The matrix analogy....
Hmmm, yes nice science fiction story, don't want to go deeper in this analogy if you don't mind.

I don't mind. I do not believe it either. I just wanted to state that nothing is 100% certain.