There is mass, distance and time

[traveler]

There is mass, there is distance, and there is time. Measure away to your little heart's content, your measuring devices will always fall short, hence there will always be something left to "prove."

 

Mass, distance, and time!

[mooeypoo]

Welcome back, traveler.

[traveler]

Welcome back, traveler.

 

Why thank you, Mooeypoo.

 

BTW, why do we consider the mass of the Earth as a point with a radius to a chosen "edge" of the object (Earth), but we stop there at the "edge" as to what is included in that object?

 

5 5 4 4 3 3 2 2 1 1 1 1 2 2 3 3 4 4 5 5

 

It's all a system.

Edited October 29, 2008 by traveler
multiple post merged

[mooeypoo]

Because that's what you define as an *OBJECT*.

 

So when you measure the object (which you have defined), you measure by your own definition. Because you are the one who defined it.

 

The sun, for instance, is harder to measure because it is gas - its "surface" is less defined. So how do you measure the "size" of the sun? You *DEFINE* the edges. You DEFINE what those edges are, so you can measure the object *YOU DEFINE*.

 

Has nothing to do with coincedence or universe or systems... or.. anything really.

 

Definitions.

[traveler]

Because that's what you define as an *OBJECT*.

 

So when you measure the object (which you have defined), you measure by your own definition. Because you are the one who defined it.

 

The sun, for instance, is harder to measure because it is gas - its "surface" is less defined. So how do you measure the "size" of the sun? You *DEFINE* the edges. You DEFINE what those edges are, so you can measure the object *YOU DEFINE*.

 

Has nothing to do with coincedence or universe or systems... or.. anything really.

 

Definitions.

 

That's the problem with defining objects as points, though, that "defined border" is a distance away from its center. That creates a bunch of problems of which include a point must also be defined, and in order to define a point it has to have a dimension, which can be halved, which makes another point a distance away form the original "point." You can't even define the point let alone define an "edge." It also creates a torque problem, because the distance changes, and torque=force times distance. Mass has force, so changing the distance changes the torque, which changes the power, as power=work/time. Another problem is that the mass at the "edge" is not at the center "point," so what do you call the sun-earth object?

[iNow]

Traveller. Stop trolling.

You've been back less than a day and already you've derailed a thread.

[swansont]

Hijacked part of thread has been moved (and infraction issued)

[mooeypoo]

That's the problem with defining objects as points, though

Which is why we don't define objects as points. Ever heard of integrals? Integrations in general? We *don't* define objects as 'points' (unless they're REAAAAAAAAAAAALLY tiny compared to the distance we measure from, and then it's done for simplicity, because the difference between a reeeeeeeeeeeeeeeeeeeeaaally faraway tinytiny object and a point-object is negligible) we look at objects as per their complexity.

 

Of course, if your life view is that everything is simplistic and uncomplicated, then you would ignore that, too, I imagine.

 

Despite what you decide to do, though, scientists don't ignore that complexity.

 

 

that "defined border" is a distance away from its center.

Again. If you look at spheres, then yes, the "border" is a distance away. If you look at non homogeneous objects, then that "border" is calculated differently. It all depends what you want to calculate, and what that object IS.

 

If we're talking about a spherical rock flying through space, it would probably be easiest to treat it as a sphere, measure its "borders" as distances from its center, etc. But what if we talk about other shapes, or, even, things that 'fall apart' and 'change shape' as they go. Like comets.

 

As it approaches the sun, a comet heats up and parts of it melt; it disintegrates, leaving a trail behind it. So: where does the comit end? In the "bulk" of it or in the tail? do you includwe the tail or not? Do you include PARTS of the tail? what about the surface? it's not easy to separate between the tail and the surface - where do you draw the line?

 

The answer isn't simple, and it depends, most of the time, on what you're checking.

 

That creates a bunch of problems of which include a point must also be defined, and in order to define a point it has to have a dimension, which can be halved, which makes another point a distance away form the original "point." You can't even define the point let alone define an "edge."

 

huh?

 

What.. what point definition? why half? what are you talking about?

There are definitions and conventions; that's how you define things, otherwise you speak philosophy and not science, and you cannot be understood by anyone.

 

It also creates a torque problem, because the distance changes, and torque=force times distance. Mass has force, so changing the distance changes the torque, which changes the power, as power=work/time. Another problem is that the mass at the "edge" is not at the center "point," so what do you call the sun-earth object?

 

Riiiiight... welcome back, traveler.

 

~moo

[Edtharan]

BTW, why do we consider the mass of the Earth as a point with a radius to a chosen "edge" of the object (Earth), but we stop there at the "edge" as to what is included in that object?

Because it simplifies the maths.

 

It does mean that we aren't 100% accurate in the calculations, but for most objects and situations this does work fine. However, there are objects and situations where this is not good enough, and in those instances the more complicated calculations are needed and we don't treat an object (like the Earth) as a single point.

 

An example is looking for oil. One way to look for oil is to look at how the Gravity changes as you pass over more or less dense regions of the Earth's crust.

 

In this you can't treat the Earth as a single point, but you have to treat it as an object with its mass spread out to its volume (and with variations in the density of this mass).

 

So, treating an object as a single point is done because it is convenient.

[mooeypoo]

The fact that we have different conventions for different tests shows that those limits are our own invention.

 

The Sun is a good example, again. When we calculate the motion of the planets around it, we tend to treat it as a round sphere. Like Edtharan pointed out, this is purely for convenience. In such examinations the 'layering' of the sun doesn't quite matter, just its total mass.

 

However, when we test things like the neutrino emissions of the Sun, or its 'sun spots', we *cannot* treat it as a homogenous sphere, we have to take into account the layers, and the gaseous "atmosphere" (over-simplification) of the Sun.

 

It would obviously be more convinient to take the Sun as a sphere in this case too, but it the innacuracy would be too great to "settle with" (unlike the first instance, where the "innacuracy" is so tiny, it's negligible). So we can't settle for convinience, and we have to take the complexities of the structure of the Sun. And we do.

 

So these things are not "black and white" as you tend to present them, traveler. We don't do just one thing all the time. We vary, and those variations depend on what we look for and how much error margin it will produce.

 

Up to highschool kids are taught that Newton's laws are F=ma and such, even though that's *not quite* Newton's law. Newton's law in the "better" form (or rather, the original, more accurate form) is more like

[math]F=m\frac{d^2x}{dt^2}[/math] (and even that's not quite it, the actual one, if I remember correctly, came from momentum. Physics expert, correct me if I wrong).

 

But highschool/elementary-school kids are not in a high-enough level to handle Newton's laws in its true form, so for simplicity, they're being taught the simplified *inaccurate* form. We CONSCIOUSLY chose to over-simplify things - on the expense of accuracy! - for children and teens, because we prefer they understand the general concept first, and then, later, in college/university/advanced courses deal with the much more complex (but accurate) representation of that law.

 

 

It's all about what you want to check, and what is the convenient way of getting it.

 

~moo

[D H]

BTW, why do we consider the mass of the Earth as a point with a radius to a chosen "edge" of the object (Earth), but we stop there at the "edge" as to what is included in that object?

We do things like that as a simplification to teach students who don't have a grasp of higher mathematics needed to model things more accurately. We do that professionally as a simplification when all using a more detailed model does is add complexity. For example, modeling the sun as anything but a point mass is downright silly when planning a spacecraft trajectory from the Earth to Mars.

 

Or, in short

Because it simplifies the maths.

 

 

An example is looking for oil. One way to look for oil is to look at how the Gravity changes as you pass over more or less dense regions of the Earth's crust.

When I first read this I was going to add some scream icons, but then I read the next paragraph:

 

In this you can't treat the Earth as a single point

Whew.

but you have to treat it as an object with its mass spread out to its volume (and with variations in the density of this mass).

The math for doing this is far beyond most undergraduate students. The University of Texas has an ongoing modern pyramid building project involving a large number of slaves graduate students. In this project, called the Gravity Recovery and Climate Experiment, the slaves graduate students struggle valiantly to build very detailed, non-point mass models of the Earth using some rather hairy mathematics. You can read more about GRACE here.

[mooeypoo]

The math for doing this is far beyond most undergraduate students. The University of Texas has an ongoing modern pyramid building project involving a large number of slaves graduate students. In this project, called the Gravity Recovery and Climate Experiment, the slaves graduate students struggle valiantly to build very detailed, non-point mass models of the Earth using some rather hairy mathematics. You can read more about GRACE here.

 

BTW, D H, I know I'm a puny undergrad, but this is really interesting; we just learned in class something about distribution of mass (and charge, they seem to have the same general concept). The professor didn't get into it too much but he did say that dipole moment (quadruple moment, etc) define the general shape and 'distortion' of the mass. Is that what you are talking about (simply, of course, I'm sure its a lot more complicated than that) ?

 

btw.. hairy mathematics or hairy mathematicians? .. both can.. be.. uh.. challenging.

Edited October 30, 2008 by mooeypoo

[D H]

The professor didn't get into it too much but he did say that dipole moment (quadruple moment, etc) define the general shape and 'distortion' of the mass. Is that what you are talking about (simply, of course, I'm sure its a lot more complicated than that) ?

That's the end result. The zeroth moment is simply the total mass. Since there is no such thing as negative mass, the dipole moment of any mass distribution about the distribution's center of mass is necessarily zero. So the first non-trivial components of a multipole expansion of a mass distribution are the quadrupole moments (2nd degree). This model of the Earth's gravity field goes up to degree and order 2159 (plus a partial expansion to degree 2190).

 

Using these models is relatively easy. All it takes is a good spherical harmonics algorithm. The hairy mathematics is coming up with the models in the first place. The Earth is not a rigid body. There are short and long term variations in the Earth's mass distribution. Over shorter periods of time, earth tides (the entire earth, not just the oceans, heaves and buckles do to the moon and sun, by about 0.35-0.5 meters) and ocean tides really make a mess of things. Over longish periods of time, mass northward during northern hemisphere winter and back toward the equator in northern hemisphere summer. One of the goals of GRACE is to uncover climate changes based on subtle variations in how a couple of satellites orbit the Earth.

[Norman Albers]

There is mass, there is distance, and there is time. Measure away to your little heart's content, your measuring devices will always fall short, hence there will always be something left to "prove."

 

Mass, distance, and time!

 

Yes, depending on your frame of reference.

[mooeypoo]

That's the end result. The zeroth moment is simply the total mass. Since there is no such thing as negative mass, the dipole moment of any mass distribution about the distribution's center of mass is necessarily zero. So the first non-trivial components of a multipole expansion of a mass distribution are the quadrupole moments (2nd degree). This model of the Earth's gravity field goes up to degree and order 2159 (plus a partial expansion to degree 2190).

wow. Neat. Is that because of the mountains/vallies of the surface of the Earth (like, does it go this deep in terms of accuracy)?

 

Using these models is relatively easy. All it takes is a good spherical harmonics algorithm. The hairy mathematics is coming up with the models in the first place. The Earth is not a rigid body. There are short and long term variations in the Earth's mass distribution. Over shorter periods of time, earth tides (the entire earth, not just the oceans, heaves and buckles do to the moon and sun, by about 0.35-0.5 meters) and ocean tides really make a mess of things. Over longish periods of time, mass northward during northern hemisphere winter and back toward the equator in northern hemisphere summer. One of the goals of GRACE is to uncover climate changes based on subtle variations in how a couple of satellites orbit the Earth.

So, if I got this right, this distribution is a function of time, too? (again, I'm reeeeeeeeally simplifying things, I'm sure, but just conceptually it's really interesting).

And.. if we're on the subject - are those tides oscillating in some frequency (in relation to how close we are to the Sun, or our positions with the other planets) or is it completely varied due to the complexity of all the planets orbits compared to ours and the Sun's mass?

 

This is really interesting, if there are any mods awake, I'd appreciate cutting this part under a new thread

[swansont]

This is really interesting, if there are any mods awake, I'd appreciate cutting this part under a new thread

 

Done — posts copied. Discussion of earth tides and mass distributions, etc. should follow up in the new thread.

 

http://www.scienceforums.net/forum/showthread.php?t=36153

 

Let me know if other posts should be added.

[Sovereign]

There is mass, there is distance, and there is time. Measure away to your little heart's content, your measuring devices will always fall short, hence there will always be something left to "prove."

 

Mass, distance, and time!

 

When you say there is mass/distance/time do you mean they exist?

What is your definition of exist?

[Norman Albers]

"First there is a mountain, then there is no mountain, then there is...", George Harrison. There is mass, more and less. It is energy tied up in some sort of bundle, as opposed to light energy at c. The rest is relative to your measuring frame.

[elas]

In the concluding chapter of ‘Concepts of Mass’ by Max Jammer, it is clearly stated that ‘mass’ is a composite of at least two entities (Jammer defines these in terms of energies). Mass cannot exist without dimensions (distance). Time is the measurement of change (history).

It follows that if we accept the ‘conservation of energy’ law then we must accept the ‘conservation of mass’ and the overall ‘conservation of dimensions’ (divisions of infinity), and finally the ‘conservation of time’ (it is always ‘now’ anything else is history).

Surely, the conclusion to be drawn from conservation of mass, dimensions, and time; is that infinity is ‘steady state’ subject to equal and opposite local changes (such as the creation and decay of universes etc).

Edited November 1, 2008 by elas

[Norman Albers]

Yes, but there is energy-mass conversion so don't we say, there is conservation of mass-energy?

[traveler]

It really boils down to merely distance and ideas. Distance is inevitable, are ideas?

[Norman Albers]

Entanglement is.

[mooeypoo]

It really boils down to merely distance and ideas. Distance is inevitable, are ideas?

What does that even mean?

 

 

If something's standing still, there's no.. distance... or change in distance... or.. if you're standing inside something there's no distance between you and that something.

 

I don't quite get what you're saying here.

[traveler]

What does that even mean?

 

 

If something's standing still, there's no.. distance... or change in distance... or.. if you're standing inside something there's no distance between you and that something.

 

I don't quite get what you're saying here.

 

Nothing "stands still." That is an illusion.

[swansont]

Nothing "stands still." That is an illusion.

 

As long as there is no acceleration, you can't say, absolutely, who is moving.