# The earth is round

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#### TheEngineer

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##### The earth is round
« Reply #90 on: October 18, 2006, 11:48:06 PM »
Sigh...Gravity is indistinguishable from acceleration.  Einstein postulated this in Relativity.  I see now where you may be getting confused.  Let's look at the car example:
A car accelerates at 2g.  This is caused not by gravity, but by the transmission of power through the driveline.  Sitting in the car, I feel an acceleration of 2g.  Now, without any reference to the movement of the car, it is equivalent to say that the acceleration I feel is actually caused by a 2g gravitational field pulling me into the seat.

Gravity=acceleration, NOT, that all acceleration is caused by gravity.  You can't distinguish between the two.  This is what the equivalence principle is about.
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Failure to understand such a concept portrays no science skills.

I could not have said it any better myself.
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If someone actually took the effort to look into what I wrote maybe they would understand.

They would understand that you have no idea what you are talking about.
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If people here actually believe such nonsense

Now Relativity is nonsense?

Look, if you think equivalence is wrong, more power to you.  I'm sure you could get the Nobel Prize in physics by debunking Relativity.  I eagerly await your nomination.

"I haven't been wrong since 1961, when I thought I made a mistake."
-- Bob Hudson

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#### Earthisround99

• 44
##### The earth is round
« Reply #91 on: October 18, 2006, 11:58:36 PM »
You guys keep saying that bib thinks he is smarter than einstein. Well thinking the earth is flat really makes you sound like you are above him. I am sure Einstein would roll over in his grave knowing people think the earth is flat.
he earth is a cube!

#### TheEngineer

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##### The earth is round
« Reply #92 on: October 18, 2006, 11:59:56 PM »
Oh, great argument.

"I haven't been wrong since 1961, when I thought I made a mistake."
-- Bob Hudson

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#### Earthisround99

• 44
##### The earth is round
« Reply #93 on: October 19, 2006, 12:03:18 AM »
One more thing before I go. I don't wanna fill up this topic too much cause there are some good arguments going back and forth.

At Bib: No matter what you say to them they will make up some bs anwser and say they are right.
he earth is a cube!

#### TheEngineer

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##### The earth is round
« Reply #94 on: October 19, 2006, 12:05:22 AM »
Quote from: "Earthisround99"

At Bib: No matter what you say to them they will make up some bs anwser and say they are right.

I will say I'm right because Einstein says so.

"I haven't been wrong since 1961, when I thought I made a mistake."
-- Bob Hudson

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#### Who da man

• 25
##### The earth is round
« Reply #95 on: October 19, 2006, 12:05:23 AM »
Im sick of all this aguing, why dont we all just say its a cube and get on with our lives?
person without religion is like a fish without a bike

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#### Earthisround99

• 44
##### The earth is round
« Reply #96 on: October 19, 2006, 12:09:01 AM »
That is the most intelligent thing ever posted on this board. It is a fucking a cube.
he earth is a cube!

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#### bibicul

• 259
##### The earth is round
« Reply #97 on: October 19, 2006, 12:15:46 AM »
Uff, TheEngineer... To accelerate an object is to change its velocity, which is accomplished by altering either its speed or direction (like in case of uniform circular motion) in relation to time.

Do you see that 'direction' word? Yes, that's right - acceleration can be changed by changing the object's direction.

Your statement is made 'without any reference to the movement of the car'. Unfortunately I care about the movement of the car and so do physics professors who say that the TOTAL acceleration of a body is found by vector addition of the opposite of the actual acceleration (in the sense of rate of change of velocity) and a vector of 1 g downward for the ordinary gravity (or in space, the gravity there). Of course, this TOTAL ACCELERATION can be broken in TWO (obviously), depicted in a figure by two different arrows, one of them being acceleration due to gravity.

Like I said before, Einstein never said that "acceleration=gravity and vice-versa."

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#### bibicul

• 259
##### The earth is round
« Reply #98 on: October 19, 2006, 12:28:13 AM »
TheEngineer, I figured out why you are making this mistake... you are confusing the acceleration due to gravity and acceleration in general with the inertial and gravitational masses - which HAVE been proved to be the same by... yes, Einstein, in his... Theory of relativity!

Here are links for you to remember what you were taught in school:
http://en.wikipedia.org/wiki/Gravitational_mass

Enjoy!

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#### woopedazz

• 421
##### The earth is round
« Reply #99 on: October 19, 2006, 12:34:11 AM »
i think if everyone just calmed down a little, they would realise that we are all arguing for exaclt the same thing:

as engineer wrote:
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Gravity=acceleration, NOT, that all acceleration is caused by gravity. You can't distinguish between the two. This is what the equivalence principle is about.

this is exactly wat i as arguing wen i wrote gravity=acceleration, its exaclt wat enginner has been saying (he is quoted above), and its exactly wat bibicul was trying to say, albeit a little vaugely at first, but nonetheless he was in semi-agreement.

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#### woopedazz

• 421
##### The earth is round
« Reply #100 on: October 19, 2006, 12:37:43 AM »
and not in all cases is it true that equations are true in both "directions" as gravity=acceleration (for all cases), but acceleration=gravity for only some cases.

this is somewhat similar to matrices where AB does not neccessarily equal BA

in the UMAT this year there were a number of questions referring to "gooks are mooks, some mooks are pooks, some pooks are kooks; does this mean that all gooks are kooks?"and variations including "does this mean that all kooks are mooks?"

#### TheEngineer

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##### The earth is round
« Reply #101 on: October 19, 2006, 12:45:39 AM »
This is just getting stupid.  Seven pages and you still don't get it.
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Among numerous postulates, Einstein proposed the equivalence principle which states that no experiment can distinguish the acceleration due to gravity from the inertial acceleration due to a change of velocity. To illustrate that principle, Einstein used thought experiments involving elevators. He compared different phenomena related to accelerations observed inside an elevator.

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10.3 - Inertial versus Gravitational Acceleration of Masses.
Before considering the problem of photons moving with respect to an accelerated frame, let us study a mass m moving horizontally. The mass enters an elevator which has an upward acceleration a in outer space at the moment its vertical velocity with respect to the source of the mass is zero. The elevator is accelerated by a rocket placed under it to produce a force F (shown by upward arrows on figure 10.2A). Due to that force F, the elevator (and the observer) accelerates following Newton's law:
F = Ma    10.2
where M is the mass of the elevator (including the observer's mass) and a is its acceleration given by:
10.3
After a time interval Dt, the mass will hit the opposite wall. It will have traveled a vertical distance DhA relative to the moving elevator. Obviously, the mass will have traveled an absolute vertical distance of zero since there is no gravitational field.

Figure 10.2A                            Figure 10.2B

Let us consider a similar elevator located at rest on Earth as illustrated on figure 10.2B. The Earth's gravitational field accelerates the mass m toward the Earth's center. After a time interval Dt, when the mass hits the opposite wall of the elevator, it will have traveled an absolute vertical distance DhB.

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Einstein, following his usual æsthetics of simplicity, assumed the ``dilemma'' was its own solution - namely,  you can't  tell an accelerated reference frame from a reference frame in a gravitational field. This is known as the  equivalence principle:

No experiment performed in a closed system can tell whether it is in an accelerated reference frame or a reference frame in a gravitational field.

If you wake up in a closed box and you experience ``weight'' (as one normally does on Earth), there is no way to be sure you are actually being attracted by gravity, as opposed to being in a spaceship (far from any stars or planets) which is accelerating at one ``gee.'' What's more, if Einstein is right, no matter how clever you are you will not be able to measure any phenomenon from which you can tell the difference. The two cases are perfectly equivalent, hence the name of the Principle.gif

So far this Principle agrees with experiments, which has led people to look for ways to make the statement, ``A gravitational field is the same thing as an accelerated reference frame,'' sound reasonable. To make any progress along these lines we have to turn to an analysis of our notion of ``acceleration'' - i.e. of the nature of space and time, and therefore of geometry.

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The key idea of general relativity, called the equivalence principle, is that gravity pulling in one direction is completely equivalent to an acceleration in the opposite direction. A car accelerating forwards feels just like sideways gravity pushing you back against your seat. An elevator accelerating upwards feels just like gravity pushing you into the floor.

http://www.pbs.org/wgbh/nova/einstein/relativity/
http://hyperphysics.phy-astr.gsu.edu/Hbase/relativ/grel.html
http://www.einstein-online.info/en/spotlights/equivalence_principle/index.html

How about doing some research, you are doing nothing but displaying your ignorance each time you post.

"I haven't been wrong since 1961, when I thought I made a mistake."
-- Bob Hudson

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#### woopedazz

• 421
##### The earth is round
« Reply #102 on: October 19, 2006, 12:49:50 AM »
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How about doing some research, you are doing nothing but displaying your ignorance each time you post.

i sincerely hope that ur talking to him... :?

#### TheEngineer

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##### The earth is round
« Reply #103 on: October 19, 2006, 12:50:15 AM »
Yes, I am.

"I haven't been wrong since 1961, when I thought I made a mistake."
-- Bob Hudson

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#### bibicul

• 259
##### The earth is round
« Reply #104 on: October 19, 2006, 01:10:59 AM »
woopedaz, thanks for trying to calm some people down. I think that your last 2 or 3 posts explained fairly well what's going on right now.

TheEngineer, please read the vector argument that I made and think of what you learned in middle-school. I never said that you cannot calculate a total acceleration using g as one of the two vectors, but I also said that you can break it into 2, with g being PART of the total acceleration (given by adding up the 2 vectors, and therefore AN acceleration, not TOTAL acceleration and not a force, as was previously believed).

Also, if you don't stop with the insults I don't think that we should continue arguing.

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#### martianman

##### The earth is round
« Reply #105 on: October 19, 2006, 02:33:59 AM »
nobody's insulting you, you ass. stfu already and go live on your round earth or whatever.. sheesh

martian man

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#### GeoGuy

##### The earth is round
« Reply #106 on: October 19, 2006, 06:13:00 AM »
Quote from: "bibicul"
Like I said before, Einstein never said that "acceleration=gravity and vice-versa."

Biblicul, Einstein said that the effects felt by an object in a gravitational field are identical to those felt by any accelerating object. Meaning that it is impossible to distinguish between gravity and acceleration. This is why we're saying that acceleration equals gravity.

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#### bibicul

• 259
##### The earth is round
« Reply #107 on: October 19, 2006, 06:30:39 AM »
Yes, the EFFECTS THAT WE FEEL are identical, but what causes that effect is represented by two vectors, one being the gravitational acceleration towards the center of the earth and the other being the opposite of the actual acceleration (in the sense of rate of change of velocity).

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#### GeoGuy

##### The earth is round
« Reply #108 on: October 19, 2006, 07:21:07 AM »
From wiki:

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It is important to note that gravitation is not gravity. Gravitation is the attractive influence that all objects exert on each other, while "gravity" specifically refers to a force which all massive objects are theorized to exert on each other to cause gravitation. Although these terms are used interchangably in everyday use, it is important to note that in theories other than Newton's, gravitation is caused by factors other than gravity. For example, in general relativity, gravitation is due to spacetime curvatures which causes inertially moving object to tend to accelerate towards each other.

What we've been saying is that not only does general relativity state that gravity and acceleration are equal, but in so doing does away with the concept of "gravity" entirely.

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#### bibicul

• 259
##### The earth is round
« Reply #109 on: October 19, 2006, 07:28:20 AM »
Quote from: "GeoGuy"
From wiki:

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It is important to note that gravitation is not gravity. Gravitation is the attractive influence that all objects exert on each other, while "gravity" specifically refers to a force which all massive objects are theorized to exert on each other to cause gravitation. Although these terms are used interchangably in everyday use, it is important to note that in theories other than Newton's, gravitation is caused by factors other than gravity. For example, in general relativity, gravitation is due to spacetime curvatures which causes inertially moving object to tend to accelerate towards each other.

What we've been saying is that not only does general relativity state that gravity and acceleration are equal, but in so doing does away with the concept of "gravity" entirely.

Where does general relativity state that gravity and acceleration are equal (and by equal I assume you mean "the same concept") and moreso, how does it do away the concept of gravity entirely? Are you referring to the fact that gravity is no longer considered a force but an acceleration?

#### beast

• 2997
##### The earth is round
« Reply #110 on: October 19, 2006, 07:34:23 AM »
Quote from: "bibicul"
Quote from: "GeoGuy"
From wiki:

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It is important to note that gravitation is not gravity. Gravitation is the attractive influence that all objects exert on each other, while "gravity" specifically refers to a force which all massive objects are theorized to exert on each other to cause gravitation. Although these terms are used interchangably in everyday use, it is important to note that in theories other than Newton's, gravitation is caused by factors other than gravity. For example, in general relativity, gravitation is due to spacetime curvatures which causes inertially moving object to tend to accelerate towards each other.

What we've been saying is that not only does general relativity state that gravity and acceleration are equal, but in so doing does away with the concept of "gravity" entirely.

Where does general relativity state that gravity and acceleration are equal (and by equal I assume you mean "the same concept") and moreso, how does it do away the concept of gravity entirely? Are you referring to the fact that gravity is no longer considered a force but an acceleration?

Don't know how to use an internet forum and you question my intellect...

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#### GeoGuy

##### The earth is round
« Reply #111 on: October 19, 2006, 07:38:38 AM »
Quote from: "bibicul"
Where does general relativity state that gravity and acceleration are equal (and by equal I assume you mean "the same concept") and moreso, how does it do away the concept of gravity entirely? Are you referring to the fact that gravity is no longer considered a force but an acceleration?

Einstein used his theory of relativity to show that gravity, in the Newtonian sense (which is, apparently, how you see it), does not exist. And the effects we feel from gravitation are simply accelerations due to the curvature of space-time. In other words, gravity is acceleration.

Edit: I put certain parts of my original quote in bold for a reason.

#### beast

• 2997
##### The earth is round
« Reply #112 on: October 19, 2006, 07:43:14 AM »
http://en.wikipedia.org/wiki/General_relativity

" So what people standing on the surface of the Earth perceive as the 'force of gravity' is a result of their undergoing a continuous physical acceleration caused by the mechanical resistance of the surface on which they are standing."

Fairly straight forward.

#### TheEngineer

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##### The earth is round
« Reply #113 on: October 19, 2006, 02:05:07 PM »
Quote from: "bibicul"

TheEngineer, please read the vector argument that I made and think of what you learned in middle-school. I never said that you cannot calculate a total acceleration using g as one of the two vectors, but I also said that you can break it into 2, with g being PART of the total acceleration (given by adding up the 2 vectors, and therefore AN acceleration, not TOTAL acceleration and not a force, as was previously believed).

Why are you resolving the acceleration vector into components? One of them is not g.

"I haven't been wrong since 1961, when I thought I made a mistake."
-- Bob Hudson

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#### earthisroundgetoverit

##### The earth is round
« Reply #114 on: October 19, 2006, 02:16:44 PM »
get over it the earth is round...or do i need to catapult you guys into space to see it?? :twisted:

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#### Unimportant

• 1229
##### The earth is round
« Reply #115 on: October 19, 2006, 02:18:23 PM »
*drumroll*

....................and he's banned!

Congratulations!

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#### holybrain

• 89
##### The earth is round
« Reply #116 on: October 19, 2006, 02:54:27 PM »
Quote from: "Unimportant"
*drumroll*

....................and he's banned!

Congratulations!

I don't think he'll be banned, YStick hasn't been yet.
believe the Earth is round.
That doesn't mean the Earth is round.

"If you're going to yell at me every time I do something stupid, then I guess I'm just going to have to stop doing stupid things!" --Homer Simpson

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#### tycoonius

##### The earth is round
« Reply #117 on: October 19, 2006, 03:25:24 PM »
Hey. I hope this is the right thread to post this in. If you guys don't mind, I've just read through your FAQ, and I have a question that wasn't in there. I was hoping you could address it. Here it is:

If the Earth is totally flat, why is it that I cannot see past the horizon? It seems like if the Earth were totally flat, you could sail miles out to sea and still see some hint of the mainland off in the distance.

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#### GeoGuy

##### The earth is round
« Reply #118 on: October 19, 2006, 03:30:34 PM »
Even on a RE, obstructions in the atmosphere obscure your line of site long before it would be obscured by Earth's curvature.

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#### tycoonius

##### The earth is round
« Reply #119 on: October 19, 2006, 03:35:58 PM »
Quote from: "GeoGuy"
Even on a RE, obstructions in the atmosphere obscure your line of site long before it would be obscured by Earth's curvature.

Are sure about that? I've been out on a lake on a sunny day, and you can see pretty damn far. What do you mean by "obstructions" exactly?