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# Gravity on different planets?

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Why is the gravitational pull different on different planets?

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Because their mass is different.

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Why is the gravitational pull different on different planets?

1, Gravitation is directly proportional to the quantity of mass concentrated.

http://www.school-for-champions.com/science/gravity.htm

2. Bigger more dense planets have stronger acceleration fields(objects fall faster over time) than less dense or smaller planets. This has been directly observed repeatedly, including in a famous golfing experiment.

Shepherd demonstrated that the moon's gravity was approximately one sixth of that of Earth's. He was a lousy golfer. He had a mean slice.

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• 1 month later...

Many, many years ago I made my physics teacher unhappy. I asked him to consider two huge magnetic masses in empty space - each repulsive. "what would be the relative masses in order to keep them at a stable distance?" I didn't get a reply.

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Is there a point somewhere in your post? :eek2:

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Not really. Just an anecdote.

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Gravity For an interesting historical read, I recommend picking up a copy of Philosophiae Naturalis Principia Mathematica by Issac Newton.
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Many, many years ago I made my physics teacher unhappy. I asked him to consider two huge magnetic masses in empty space - each repulsive. "what would be the relative masses in order to keep them at a stable distance?" I didn't get a reply.
Since then, have you answered you own question?

The answer is a simple, unit-dependent constant relating mass^2 to charge^2 (eg: kilograms^2/Coulombs^2, grams/charge of electron, etc.). It can be calculated from the Law of Gravitation and Coulomb’s_law.

Here’s what I get (highlight to view): ~ 1.347*10^20 kg^2/C^2 or 3.457*10^-12 g^2/e^2. For example, 2 equal masses, each with exactly 1,000,000 excess electrons, should each mass about 1.859 grams.

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I cannot get my mind around magnetism. I don't understand what a magnetic field actually is. On Wikipedia, it is an 'entity'. Helpful.

I understand how it comes about and what it does well enough (for my own satisfaction).

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I know exactly what you mean! I couldnt get my head around why/how magnetism works, so I asked my Physics teacher why two opposite poles attract eachother. He tells me because they both have magnetic fields that interact with each other and cause a force that attracts the two magnets... my response 'yeah, obviously - but why?' he says 'well when we did gravity you didnt ask my why it attracts..' and I realised that I had no explanation for why gravity pulls.

so that I can get my work done I just accept it, when I get to uni I will start asking questions again. :)

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Less than ideally competent science teachers

Many, many years ago I made my physics teacher unhappy. I asked him to consider two huge magnetic masses in empty space - each repulsive. "what would be the relative masses in order to keep them at a stable distance?" I didn't get a reply. …
… so I asked my Physics teacher why two opposite poles attract eachother. He tells me because they both have magnetic fields that interact with each other and cause a force that attracts the two magnets... my response 'yeah, obviously - but why?' he says 'well when we did gravity you didnt ask my why it attracts..' and I realised that I had no explanation for why gravity pulls. ...
Geokker and Jay-qu appear have experienced the unfortunate consequences of having had Less than ideally competent science teachers. Having spent several years tutoring people who were, in all likelihood, going on to teaching careers, I know this to be unfortunately an all-to-common occurrence. :)

Have heart. Study the Standard Model, bearing in mind that, at least for magnetism, it currently offers an entirely rigorous, if complicated and difficult to learn, explanation of all of the known forces except gravity (and is groping toward an explanation of that), in which field are merely descriptive labels, not fundamental properties.

Not to mention, you have at your disposal resources like wikipedia, and your friends here at scienceforums! :)

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Indeed I did have poor quality science teachers in school. I have a conspiracy theory why education is so poorly financed but that's for another forum!

Taking you up on your last sentence, what is a magnetic field?

I have a very basic grasp of atoms, electrons, electromagnetic forces etc. Where my understanding flails about is trying to imagine what's going on between two massive objects in space causing them to drift together or magnetic fields.

It's all very well to explain the effects of electrons, but what is actually being exchanged - if anything?

I can push about a bit of metal with a magnet - what is pushing? Don't say 'the magnetic field!' - What IS it? Phontons - how can something have no mass? Must I accept a religious answer?

I assume no one knows this. Had Einstein lived long enough to explore it, perhaps we'd have a glimpse.

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Taking you up on your last sentence, what is a magnetic field?

I'm all ears to...

My teachers are great for getting what I need for passing my exams, but extending beyond that there arnt much good - My chemisty teacher didnt know what anti-matter was, and my Physics teacher hates QM because its to abstract... :)

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… what is a magnetic field? … It's all very well to explain the effects of electrons, but what is actually being exchanged - if anything?
According to the Standard Model, a magnetic field is a description of the potential interaction of fermions – predominantly electrons, up quarks, and down quarks – via the exchange of bosons responsible for magnetic force – photons.

If you try to think about this in classical physical terms, considering the fundamental particles of the Standard Model to be localized and have physical dimensions, it makes no sense – the “particles” of Particle Physics are actually quantum wave functions, effectively “as large as they have to be” to produce the observed interactions.

:) This marks the point where my understanding of the formalism of quantum mechanics in inadequate to explain more, and, like a less than ideally competent Science teacher, I have to just wave my hands and say “if you understood this stuff, you could explain it.” I truly wish I could go on, and intend to gain the understanding necessary, but the necessary mathematical formalism is hard.

Much as I’d like to avail myself of a traditional, classroom-based education, it appears that, at least for the next few years, I’ll have self-educate in my spare time. A good starting point, about as far as I’ve gotten so far, it to gain a familiarity with the fundamental particles and their interactions.

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