Q & A: Gravity vs. Magnetism

Thanks to Welshineire for taking this forum to the next level of intellect - it won't be long before Stephen Fry drop's by to answer some of our deep and well thought out questions.

Anyway, Welshineire's thread of magnetism got me thinking - what is the difference between Gravity and Magnetism and do they use the same laws of physics?

Well, here is a little Q&A that I personally wrote up.....

Q:
where does gravitational/magnetic force originate from and why does all matter get pulled by gravity(which is magnetic i believe) yet only certain metals only appear(ferrous)to get attracted to magnets and other forms of matter like wood or plastic,etc don't seem to get pulled by magnets? chris (age 10) Halifax, Canada ...AND... I wanted to ask what the difference is between a magnetic force and a gravitational force. If there's no difference, I'd like to know how come the Earth's gravitational pull is able to attract non - magnetic materials e.g human beings, yet no matter how much powerfull a magnet is it can never attract non - magnetic(non- ferrous) material.
- curious starvos (age 12)
Kenya
A:
Chris & Starvos -

Since your questions are roughly the same, I'll answer them both at once. Gravity and magnetism are not the same thing. In fact, they are completely separate forces. Gravity is a force that acts between any two objects with mass. No matter what they are made of, both objects get pulled towards each other just because they have mass. The reason it seems like gravity only pulls you towards the earth is because the earth is so big that the pull from you on it isn't enough to do much to its motion.

Unlike gravity, which occurs between any objects, magnetism depends on specific properties of objects. Magnetism can either pull the two objects together or push them apart, depending on which way the magnets point. Most importantly, it depends on what is going on with the electrons in the material, since each electron is like a tiny magnet itself. Most materials are almost insensitive to magnetism because the electrons act like magnets pointing every which way, more or less equal numbers pulling or pushing.

In some materials, the electrons can lower their energy by lining up magnetically into magnetic domains. In each domain, most of the electrons pull and push together, so you can get big forces. In some materials (permanent magnets) the domains can all be lined up so you get really big magnetic forces. If you measure very carefully, however, you find that there are small magnetic forces between magnets and 'non-magnetic' materials like pieces of copper or pieces of wood or people. Some of those 'non-magnetic' things are attracted to magnets and others are repelled.

By the way, only some ferrous materials are magnets, and only a few magnetic materials are ferrous.

Both magnetism and gravity can affect objects at a distance. Both get weaker as the objects get farther apart. This is why you are affected by the pull of gravity from the earth, but not from distance planets. It's also why two magnets may move together if you set them near each other, but if you set them far apart nothing will happen. However, as two objects get far apart, the gravity between them goes down by a factor of four when you double the distance, but the magnetism goes down by (at least) a factor of eight. On the scale of the solar system, with planets far apart, gravity is much more important than magnetism.

For more information on these forces, you can search this site.
-Tamara (and mike)
(published on 10/22/2007)

Follow-Up #1: magnetism and gravity

Q:
Why is magnetism only one direction, should there not be a third direction or more. why only north to south. Does it have another dimension. Why are we trying to explain gravity through means of mathematics, has maths evolved enough.
- brett kendall (age 46)
johannesburg, south africa
A:
Brett- Magnetic fields can align along any direction. We call the two poles of a magnet "north" and "south" as a way of keeping track of which would be attracted which way in the presence of the Earth's magnetic field. When the Earth's field reverses, those names will be awkward.

Math has certainly evolved enough to do a very good job of describing gravity. For most purposes Newton's calculus and force laws, more than 300 years old, work well. For greater accuracy, one needs General Relativity, but even that uses math that had already been developed before 1917.

It may be that for extremely small distances and extreme situations, a new theory (perhaps a string theory) will be needed, and some new math will have to be developed.

Mike W.

(published on 01/28/09)

Follow-Up #2: Repulsion of gravity?

Q:
I know it sounds like sci-fi but if you have opposite poles to magnetism and they either repel or attract each other would it be possible that the same is true for gravity or am I talking apples and oranges here? Maybe we just haven't discovered it yet, or maybe it's a theory that we just haven't figured out how to achieve physically yet?
- Derrick (age 30)
Lake Charles, LA USA
A:
This a very interesting question. We know that two like-sign electrons, or positrons repel each other whereas an electron is attracted to a positron. This is the nature of the Coulomb force of electricity: like-sign charges repel, unlike sign charges attract. The extension to the forces between magnets is straightforward. We also know that two chunks of ordinary matter attract each other. You might ask the question, 'does a chunk of ordinary matter attract or repel a chunk of anti-matter' ? Curiously, the answer is they still attract each other. Now the reason for this is pretty obscure and has to be explained by quantum field theory.
The electromagnetic force is transmitted by exchange of spin 1 quanta called photons. The gravitation force is transmitted by exchange of spin 2 quanta called gravitons. The difference between spin 1 and spin 2 makes all the difference.
See: http://en.wikipedia.org/wiki/Graviton for information on the graviton

If you don't follow all of this, don't worry. I had to go and ask our local quantum field theorist guru for an explanation a few years back when a similar question came up.

LeeH

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I hope everyone found this thread helpful. Here's a link to read more - http://van.physics.illinois.edu/qa/listing.php?id=19810

QI re. Gravity, fact fans.......

http://www.comedy.co.uk/guide/tv/qi/episodes/7/12/

I liked this:

In 1784, Britons George Biggin and Letisha Sage performed not only the first hydrogen balloon flight, but could also be argued to be the first members of the "Mile High Club" by having sex in their balloon. It was organised by an Italian called Lunardi who was meant to go with them, but he got out thinking the balloon would not support three people. He got out just as it took off in St. George's Fields, and as the balloon flew over Piccadilly people could see Sage on all-fours, although she tried to make excuses claiming she was not having sex. The balloon travelled 14 miles, landing in Harrow.
The incident became a huge scandal, with people asking having sex in a balloon was possible at all. The wager books, which contain lists of all the bets made in London clubs, contained one bet which read: "Lord Cholmondeley has given two guineas to Lord Derby to receive 500 guineas whenever his lordship 'plays hospitals' with a woman in a balloon 1,000 yards from the Earth."

I in fact had elective surgery to remove my animal magnetism.. The crotch of my work trousers still attracts flies though

Really very informative thread.I like this thread.

Tiara