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Old Jul 7th 2018, 10:37 AM   #11
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________Try to make a definition

You must admit it is pretty bad when science cannot even give a universal quality definition of up and down in 2018 to students?

Requesting forum ridicule, let me give it a shot.


Up: Pointing away from a detected center of a gravity well.


Down: Pointing toward a detected center of a gravity well.



A good definition means the words also work in the real world not just in theory. I have not thought of a scenario yet, that these do not fit, can anyone tell me one? Can these definitions be more accurate or shorter?

This works for a professor putting up and down arrows on a blackboard or in the space station. Inside the space station these definitions tell you without a detected gravity well center there is no up or down which is of course correct. If you look outside you see the Earth and know its gravity well is in its center so that is down. You are up above this.

Also looking out to the moon, you can tell up and down on the moon, with these definitions. It also means the black hole at our Galaxy center, after now detecting it, is down and we are up from it. Pointing at it with a telescope we assume it must be a gravity well (theoretically detected).

Another part of these definitions is that if you are standing in Kansas you know down is the center of the earths gravity well. You also know that a Chinese man, on the other side of the world, that up and down is defined the same. Note: pointing does not require acceleration in any form.

Once completed by members of forum perhaps we can post suggest to at least Wickipedia a modern universal definition of Up and Down? And have it supported by the people of this forum?
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Old Jul 7th 2018, 03:20 PM   #12
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Originally Posted by lancew561 View Post
You must admit it is pretty bad when science cannot even give a universal quality definition of up and down in 2018 to students?

Requesting forum ridicule, let me give it a shot.


Up: Pointing away from a detected center of a gravity well.


Down: Pointing toward a detected center of a gravity well.
But what happens when you need to define up and down both in London and Beijing? Your proposed direction for up is different in each city. You can locally define up and down but there is no Universal definition. Once you pick a coordinate system then you have to stick to it.

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Old Jul 7th 2018, 08:51 PM   #13
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_____________Point of Origin_________

Yes Up/down does change at different points but if you set coordinates in London then take them to Bejing they would function the same would they not?

Down is still the center of a sphere gravity well. What you see when you look up/down is a different matter.

It makes math input the center of chosen gravity well in the coordinates.
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Old Jul 7th 2018, 09:41 PM   #14
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Originally Posted by lancew561 View Post
Yes Up/down does change at different points but if you set coordinates in London then take them to Bejing they would function the same would they not?

Down is still the center of a sphere gravity well. What you see when you look up/down is a different matter.

It makes math input the center of chosen gravity well in the coordinates.
If I am understanding you correctly you are saying that if we set "up" (+ r direction) in London then we still need to refer to "up" to that in London. If that is so then, yes, you've got it. (ie. Beijing's "up" is not the same as that in London.)

But what if we have two objects, such as the Earth and Moon? In this case we can set various directions of up in any arbitrary direction. (In this case you might define up to be in the direction perpendicular to the plane of revolution.) The nice thing is you can define up to be in a "nice" direction, that is in any direction that might simplify the Math.

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Old Jul 8th 2018, 04:34 AM   #15
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And yes I do believe definition is most important frankly seeing science for years using many terms which are really not well defined to old or modern physics.

Yes I agree with this,

Originally Posted by lancew561 View Post
If so then define what Up and Down is?
But I think your example is not a good one since it refers to a general term which depends heavily upon context.

Up/down is a direction chosen (picked out) by the author for some purpose.
It is up to the author to explain the context of his purpose.

Without this the term is meaningless in both English and Physics.

I could give lots of examples, but I also consider this to be off topic and deserving of a thread in its own right.

I say off topic because I don't fully understand what the OP means and Jim (who is usually very down to earth (pun intended) about his utterings) has not come back on this one.
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Old Jul 8th 2018, 08:36 AM   #16
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____________How about this?_______________

After reconsideration Quark is correct it has the same problem as Einstein special relativity.

It is relative to the observers point of reference.

Down: At observers coordinates pointing toward a detected gravity well center is down.

Up: At observers coordinates pointing away from a detected gravity well center is up.

Pointing toward plane of object rotation is actually creating a horizontal line through the center of the gravity well. Problem is not all gravity wells are known to rotate?

Wish we didn't have to limit the definitions to the observer coordinates but I cannot think of another way can anyone else?

If you read the title of this thread is not knowing what up and down is relevant to the discussion?
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Old Jul 8th 2018, 08:54 AM   #17
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Originally Posted by lancew561 View Post
After reconsideration Quark is correct it has the same problem as Einstein special relativity.

It is relative to the observers point of reference.

Down: At observers coordinates pointing toward a detected gravity well center is down.

Up: At observers coordinates pointing away from a detected gravity well center is up.

Pointing toward plane of object rotation is actually creating a horizontal line through the center of the gravity well. Problem is not all gravity wells are known to rotate?

Wish we didn't have to limit the definitions to the observer coordinates but I cannot think of another way can anyone else?

If you read the title of this thread is not knowing what up and down is relevant to the discussion?
Some uses of the terms up and/or down have to do with gravity, but not all.


Consider a geophysicist standing on the Earth's surface, holding a map.

He desires to travel up, on the map or the Earth's surface?

Which way is that?

On the surface it is in the direction of increasing latitude, along an equipototential gravitation line.

On the map it is towards the North or top of the map.

But if he tupns the map through a right angle so North is now to one side, up is now to his left or right.

Returning to the Earth's surface.

Having reached his destination, the geodicist sets up a theodolite.

Is the vertical through his theodolite pointing up and down by your definition?

Or is it normal to the geoid (ie gravity) at that point?

But now he is standing at in a valley between two mountains.

He next desires to go to the top of one of the mountains.

Should he go up or down?

Last edited by studiot; Jul 8th 2018 at 08:58 AM.
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Old Jul 8th 2018, 09:06 AM   #18
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There are often issues with defining naming conventions for coordinate systems.
The key is in the word "convention"
Different people may choose different conventions.
The issue arises when it is assumed that the convention is known or just so obvious that is just unnecessary to bother defining it in detail.

As Studiot says it is important that any situation requiring a co-ordinate system includes a clear definition of the system chosen for that situation.
It is probably impossible to define a convention that will work for every situation.

I work in aerodynamics,
Experimentalists (generally) define the positive longitudinal direction as being the direction the aircraft is moving relative to the air,
Computational Aerodynamists (typically) define the positive longitudinal direction as being the direction the air is moving relative to the aircraft.
This does cause confusion when the two meet!
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Old Jul 8th 2018, 09:10 AM   #19
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______________Why we need a definition_____

This is a perfect example of why we require a definition.

By these new definitions there is no such thing as up or down on a map only top, bottom, right or left. Toward the north is not up but just toward what the map calls north. We all know north is not up.

By these definitions up means away from center of gravity point and yes we use the words Up/Down now incorrectly all the time.

Studiot makes a really great point of how the terms have been misused forever due to a lack of quality definition.
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Old Jul 8th 2018, 09:58 AM   #20
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Originally Posted by lancew561 View Post
This is a perfect example of why we require a definition.

By these new definitions there is no such thing as up or down on a map only top, bottom, right or left. Toward the north is not up but just toward what the map calls north. We all know north is not up.

By these definitions up means away from center of gravity point and yes we use the words Up/Down now incorrectly all the time.

Studiot makes a really great point of how the terms have been misused forever due to a lack of quality definition.
Thank you both.

Although I agree that some terms have been used in an unfortunate manner, you did not fully appreciate what I said, and made no response to my question about the theodolite.

This was a rather technical subtlety so I will find a better one.


Woody, interesting occupation.


Thank you for using the word aircraft.


This illustrates nicely my point that there are more meanings than words and we deal with that in a variety of ways.

One way is for some words to have more than one meaning.

Another way is for there to be a hierarchy of terms, each level being more restrictive.

Yet another way is the use of auxiliary words.

Which way does an aircraft go when taking off?

I do not think anyone would be confused by saying up.


But the term aircraft is an example it is a general term that includes winged aeroplanes, balloons and helicopter type craft.


When one takes of it may go straight up or at a climb.


Immediately we have an example of an auxiliary word used with up.




I honestly don't know of anyone being confused by what is meant by up, although it can be difficult to know which way that is when diving.




But the term vector brings much confusion as does the term field.
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