Gravity on different planets?

[shanowa]

Why is the gravitational pull different on different planets?

[Tormod]

Because their mass is different.

[damocles]

Originally Posted by shanowa

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.

http://www.xs4all.nl/~carlkop/golf.html

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.

[geokker]

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.

[Tormod]

Originally Posted by geokker

I didn't get a reply.

Is there a point somewhere in your post?

[geokker]

Not really. Just an anecdote.

[C1ay]

Gravity For an interesting historical read, I recommend picking up a copy of Philosophiae Naturalis Principia Mathematica by Issac Newton.

[CraigD]

Originally Posted by geokker

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.

[geokker]

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).

[Jay-qu]

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.