I Why does Kepler's Third Law exist?

[sophiecentaur]

Keep being curious. Keep asking questions.

That's easy to say but we all know that learning by just asking questions seldom gets us very far. That is not much further than pop Science on the TV which may be 'enough' to enjoy the edited bits of Science but it never allows one to make valid predictions or conclusions.

To know the appropriate questions to ask, you must first have learned a significant amount. Q and A is very high risk.

 

[topsquark]

That's easy to say but we all know that learning by just asking questions seldom gets us very far. That is not much further than pop Science on the TV which may be 'enough' to enjoy the edited bits of Science but it never allows one to make valid predictions or conclusions.

To know the appropriate questions to ask, you must first have learned a significant amount. Q and A is very high risk.

I agree. It sounds to me like he's at the beginning of all of this. A teacher in an organized course is the best thing for him. I guess I'm assuming he already knows that and would be taking a course at some point so I didn't bring that up.

-Dan

 

[Vanadium 50]

The inverse square law of light is an equation too, but it can be intuited with a model and some geometry.

You mean A = 4\pi r^2? Looks like an equation to me!

 

[DaveC426913]

You mean A = 4\pi r^2? Looks like an equation to me!

It is.
But the phenomena itself can be intuited with the use of a visual aid, like so:

Sure there's technically a bit of simple math there, but 99% of the meaning of the equation is embodied in the geometry of the diagram.

 

[PeroK]

I am studying with the OU ...

I strongly suspect the OU physics course will include some equations.

 

[sophiecentaur]

A teacher in an organized course is the best thing for him.

I think you could be being a bit more polite than I. I would suggest that "best' should be replaced with "essential" for whoever wants PF advice. It is mostly hard stuff and very little of it avoids Maths.

Even @DaveC426913 's diagram is 'maths' - just dressed up in a more friendly way.

 

[DaveC426913]

Even @DaveC426913 's diagram is 'maths' - just dressed up in a more friendly way.

Agree. I just think it's the level of maths the OP is looking for.

 

[Martyn Arthur]

I continue to be profoundly grateful for your patience of you all, the recent posting reassured me that I am not being regarded as a 'nuisance'.
May I please approach this from a different perceptive, forgetting Kepler and equations completely?
Separately [as a comparison] the relationship between the distances between Earth, the Sun, and the Moon are, without any 'apparent' reason such that eclipses are caused to occur.
It could then follow that the explanation for the two of the two minor bodies relative to the sun is a simple consequence of the compound gravitational forces acting in accord with the gravitational constant.
There is a gravitational constant, it is what it is, and we do not seek further.

Likewise is it the case that the defined relative orbiting situations, in a particular mode/sequence, are a physical result of the gravitational constant et al.

From my perspective, objectively / simply of trying to understand.
I am trying to pitch this in the most basic format. is the specific relationship between orbital relationships defined by science [then as defined by Kepler, not forgetting ever Newton, or is it just the way it is?
Martyn Arthur...thanks ongoing for the patience and understanding of you guys,
Martyn Arthur [agan]

 

[DaveC426913]

It could then follow that the explanation for the two of the two minor bodies relative to the sun is a simple consequence of the compound gravitational forces acting in accord with the gravitational constant.
There is a gravitational constant, it is what it is, and we do not seek further.

That our Moon often eclipses the Sun is a matter of coincidence - there's no deeper factors*. There's lots of Moons, and they inhabit a wide range of distance from their primaries.

*(I mean, except for the usual limits on multiple body systems: a moon can't get too far from its primary or it won't have a stable orbit, and it can't get too close or it will disintegrate.)

 

[sophiecentaur]

Separately [as a comparison] the relationship between the distances between Earth, the Sun, and the Moon are, without any 'apparent' reason such that eclipses are caused to occur.

You are seeing something significant here but is it really? Should there be an "apparent reason" why two sixes turn up together? There is a perfectly reasonable explanation of the way the Solar System was formed in a rough disc shape (do some Googling about it). That means that most of the objects orbit round the Sun near to its equatorial plane. Also, most of the planets rotate (and their moons) with axes much the same as the axis of those orbital planes. To get an eclipse, all that's necessary is for a large (or just large enough) object to pass between the Sun and another object. That will cause the object (or part of it) further away to be briefly in shadow. Solar Eclipses are very impressive because the Sun is a major part of our visual experience and the eclipse is total (but not always). Every so often, other objects go across the Sun (from our POV). Transits of Venus are quite common.

 

[sophiecentaur]

is the specific relationship between orbital relationships defined by science [then as defined by Kepler, not forgetting ever Newton, or is it just the way it is?

Everything in our lives is "the way it is". Science attempts to apply models to help us predict what will happen or explain what has happened in terms of those models. That's all. You will appreciate that most of those models involve Maths and Maths is a lot more reliable than arm waving.
Hopefully you will get more familiar and competent with Maths or your personal picture of Science will be limited to stuff that Science Journalists provide.

 

[Martyn Arthur]

erm... reference "the gravitational force is proportional to mass, as is acceleration, according to Newton's laws of gravity and motion respectively. The motion of bodies under the force of gravity, whether parabolic projectile motion or elliptical orbits, is therefore independent of the mass of the body."
Given the standard equation F = G(m1m2)/R^2 how can the mass of a body under the force of gravity be irrelevant?
An increase in the mass of a body orbiting the sun would change the relationship.

 

[sophiecentaur]

erm... reference "the gravitational force is proportional to mass, as is acceleration, according to Newton's laws of gravity and motion respectively. The motion of bodies under the force of gravity, whether parabolic projectile motion or elliptical orbits, is therefore independent of the mass of the body."
Given the standard equation F = G(m1m2)/R^2 how can the mass of a body under the force of gravity be irrelevant?
An increase in the mass of a body orbiting the sun would change the relationship.

You would normally read, along with this statement that it only applies for small bodies on much larger ones - as with artillery shells and the Earth or the Earth orbiting the Sun. It's valid for so many situations that people can be a bit sloppy about using the caveat.
Your version of the Force equation is more like the correct one. It's only correct when the bodies can be considered to be point masses.

 

[Martyn Arthur]

That's fair thanks, now reading well ahead into my course I read that the K3 relationship is defined as a consequence of the gravitational effect on orbiting bodies, which seems to tie in with my understanding that K3 demonstrates a factual situation, a relationship that is a consequence of the gravitational consequence of the masses of bodies orbiting, here the sun.
Please I just want to understand, is it the case that K3 demonstrates that the orbital periods of bodies orbiting the sun are a direct consequence of the relationship between the masses of those bodies and the mass of the sun.
Hence there is a rule that would extend to all bodies with an orbital relationship.
Hence if the mutual gravitational force is too weak the orbiting body exits the orbit, if too great it crashes into the central object, else it occupies an orbital period commensurate with the model prescribed by K3.

 

[sophiecentaur]

Sorry but you are demonstrating that , without the Maths as a model, one can drop into a black hole at any minute.
If you gave the Sun twice the mass, K3 would still apply - just with reduced orbital radii. The ‘equation’ is the only way to communicate something like this. You keep demonstrate this. Wait till you have the Maths and it will all be clear.

 

[Martyn Arthur]

Guys, I thought this forum was for anyone seeking to understand.
If you were giving an introductory talk to a class of 14-year-olds in a school how would you explain things, or having regard to a couple (just a couple of earlier comments) is this below this forum?
My undergraduate stating second-year course says the relationship is essentially due to the effect of gravitational forces why do you find it so impossible to quantify the core figures, or indeed are they not known?

 

[sophiecentaur]

What “core figures’” are unidentified? We know G and the mass of the Sun. Afaik, you can build a pretty good solar system. Taking each planet on its own and its orbit radius (assuming circular).
You need to improve that for elliptical orbits and further by including planetary interactions.
Or do you want a model that starts with primeval disc of gas and dust and yields the present structure? There are too many variables for that. Also, all exoplanet systems are different. So they where do you want to go with this? The answer is not 42. ;-)

 

[Doc Al]

Enough already. This thread is done.