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Old Jul 8th 2018, 10:12 AM   #21
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__________Convention__________

Convention for Up/Down usage will now only be valid per the definition and hence everyone (maybe in 10 years) can apply the same usage.

If you are in a valley, it is down compared to the hill, since the hill is pointing farther away from the center of gravity well then the valley. So yes you can go up the hill. That fits the new definitions.

When in R&D for aircraft guidance transmitters i.e. the ground base VOR we spent quite a bit of effort just trying to define the logic value point for a control computer of high or low (back in 1980s). Like, when is 5 volt logic considered a high and when a low. If this had been defined before it would be a universal standard.
Is above 2.5 volts a high and below 2.5 a low or is there an undecided area for example.
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Old Jul 8th 2018, 10:41 AM   #22
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Originally Posted by lancew561 View Post
Convention for Up/Down usage will now only be valid per the definition and hence everyone (maybe in 10 years) can apply the same usage.

If you are in a valley, it is down compared to the hill, since the hill is pointing farther away from the center of gravity well then the valley. So yes you can go up the hill. That fits the new definitions.

When in R&D for aircraft guidance transmitters i.e. the ground base VOR we spent quite a bit of effort just trying to define the logic value point for a control computer of high or low (back in 1980s). Like, when is 5 volt logic considered a high and when a low. If this had been defined before it would be a universal standard.
Is above 2.5 volts a high and below 2.5 a low or is there an undecided area for example.

I still can't see where your examples are confusing anyone (except perhaps yourself ? )

Yes there are other words associated with up/down such as above and below, high and low and so on.


And some of these have nothing to do with gravity.


Here is another one.


I am pumping water uphill, against gravity.


So the flow is uphill.


So upstream is downhill and downstream is uphill!



Yes the mountain is above the valley, but not directly above in the sense that a line through from the mountaintop through the valley bottom does not intersect the centre of gravity you keep referring to.
Yet it I still considered down from the mountain to the valleu.


And no one is confused



And you still haven't addressed my theodolite question.
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Old Jul 8th 2018, 10:42 AM   #23
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____________theodolite____________

Theodolite usage pointing straight up/down fits the new definitions does it not?

If pointed at an angle, it is not pointing to true up, but at an angle to its reference point (center of gravity well). This means it is pointing partially up and partially down.
The definitions allow something to point up and down at the same time.

The word aircraft is almost self defining and better than most words at self description. A craft that travels through the air. Better if it was craft that travels through an atmosphere since now it can be on other planets. The word aircraft had to be updated since not totally universal.

Many science definitions (the good ones) have universal definitions do they not?

Yes you are pumping water uphill farther away from the center of gravity hence it is going up...........How can you have Up and Down without a gravity well?

I am not trying to confuse, but putting in an effort, hopefully including everyone I can, to provide a universal definition that lasts.

Last edited by lancew561; Jul 8th 2018 at 10:54 AM.
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Old Jul 8th 2018, 10:56 AM   #24
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But down stream is measured in the direction of flow, which is up hill.


But only up hill in this case, since I could be pumping horizontally or even downhill.

Which is why I say you have to have the context to complete the meaning.


And no it is clear that you do not understand what I said about the theodolite.

I will see if I can post a diagram.
There is a specific formula for the difference between the theodolite 'up' and the normal to the equipotential, although the difference is small enough to ignore in all but geodetic work.
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Old Jul 8th 2018, 11:25 AM   #25
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___________Edit the Definitions?______

I am not disagreeing with you studiot that the definitions may still require
some adjustment. Not trying to define this totally on my own.

Please do not tell me impossible because you are saying we cannot define up from down. Does that sound scientific to you? Rather believe with me that in this forum we might at least have a good chance?

Please go ahead and redefine up/down definitions where you see problems.


Lance
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Old Jul 8th 2018, 11:35 AM   #26
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Originally Posted by lancew561 View Post
I am not disagreeing with you studiot that the definitions may still require
some adjustment. Not trying to define this totally on my own.

Please do not tell me impossible because you are saying we cannot define up from down. Does that sound scientific to you? Rather believe with me that in this forum we might at least have a good chance?

Please go ahead and redefine up/down definitions where you see problems.


Lance
No I am saying you seek a cut and dried, black v white definition for a very general word with a wide range of usage.


That is not possible, but there are ways that we deal with this.


Context is the most important of these and context, by its very nature, cannot be included in a definition.
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Old Jul 8th 2018, 12:07 PM   #27
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_________Great News_____________

Studiot has just given the perfect examples of how many people for years have taken the words up/down in context and in error with science.

This further confirms the new definitions to be correct.......

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.


Any other suggestions welcome?
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Old Jul 8th 2018, 12:46 PM   #28
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I keep saying you should beware of gravitational references and here's why.

It is also the detail of the theodolite question I asked.


In the first sketch the Earth is shown as a dashed sphere.

But it is not a sphere. It is (almost) an ellipsoid.

So I have drawn the ellipsoid as a continuous line ( but with a common centre) and picked out a general point A on the surface.

The point of this is that a perpendicular at A on the ellipsoid

does not pass through the centre

as it would for a perpendicular if the Earth was spherical.

So now we have two candidate lines AO and AB for the line of up and down.


But wait on - it gets worse.


That was for a non spinning Earth.

But the earth is spinning.

So at the general point a body experiences not only the 'real' pull of gravity but a centrifugal force cf as shown in the second diagram.

These two combine vectorially as shown to create a third line AC along which the apparent gravity acts.

So which one of these three (AO, AB or AC) do you want to choose for your exact tight definition?
Attached Thumbnails
"What IS and What IS Not"-gravdirection1.jpg  
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Old Jul 8th 2018, 06:54 PM   #29
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__________Center of Gravity Well__________

In the definition there is no difference where the gravity well center is.

If shaped like a potato on the outside, it does not matter, since the gravity well center is used as the reference point for up/down. No matter where the center of gravity well is, by these definitions, it is the up/down point.

A reading of say down assumes at light speed that the center of gravity remains mostly constant while pointing at it otherwise it becomes more difficult to point to exact down with center fluctuations.
That is now what I think you are saying studiot?

This makes good sense and demands a correction to the up/down definitions like within an error of ? or other short worded method to correct
them. Will consider and does indicate a definition problem.

Something like subject to center of gravity well fluctuations.
Which is a bit long to add? etc.?
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Old Jul 8th 2018, 09:30 PM   #30
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Originally Posted by lancew561 View Post
Studiot has just given the perfect examples of how many people for years have taken the words up/down in context and in error with science.

This further confirms the new definitions to be correct.......

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.


Any other suggestions welcome?
But what if there were more than one object? Say, Earth and Moon. Which gravitational center do we use?

The point I was making earlier is that you need to choose an origin... it does not really matter what direction you choose so long as you always use that choice for the rest of the problem.

Now, consider just the Earth. If we choose "up" to be the direction opposite from the direction to the center of the Earth at that location then what is "up" on the opposite side? Your convention claims both are up though they clearly aren't pointing in the same direction.

It's best not to have a convention that covers all problems as you can't figure out a coordinate system to be the same for all problems. Just pick one and go for it.

-Dan
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