What is Chi

[Tovath]

Now we all know that Ranma uses chi in his attacks. Does anyone know how it is alike and different from magic.

[Metroidvania]

Ki is always internal, and sometimes (chi) spiritual in format, and is usually formed by meditation after training one's body extensively, at least, from what I've read. I'm sure others have more in-depth explanations.
Magic on the other hand, is wild. It can be either internal, linked to another power source. (i.e. SM or Slayers), or even so common that anyone can use it.
Do you mean to leave the terms so broad?
Because if you do, magic differs almost infitesimally in its explanations, and chi/ki usually has many different definitions as well.
In other terms, did you mean to be a bit more specific, as to help with better comparisons?

[Pale Wolf]

There are no differences.
Rumiko never bothered to define the power source she was giving to Ranma. Nor did Naoko do so (assuming this is your R/SM cross).
You decide.

[Tovath]

Metroidvania No I didn't mean to be real broad it just came out that way because I am not sure how to ask it. how about this in healing Ranma and the others seem to be able to use their chi to heal them selves and we know that Hotaru can heal other people how is what they do different.
Wolf I think Rumiko never defined chi because it is well known in Japan unlike over here I think

[Bliss]

It also depends on the culture, philosophy and religion you're coming from. The Taoist concept of Qi is different from say the Buddhist, or the Confucian ideal.
Here is a generalized overview that should help, although if you wish for something further, I can only help on the Chinese concept, not the Japanese version which I think is what you're looking for.

[Pale Wolf]

Wolf I think Rumiko never defined chi because it is well known in Japan unlike over here I think

It is well-known in Japan, and has nothing to do with throwing balls of energy, creating hurricanes, or poking things till they explode.
In other words, she hijacked a term and then went wild with it. So really, Ranma's chi has jack-all to do with the real meaning except that it's associated with martial arts.

[Alathon]

It's an eastern myth, along the lines of "humors" and other concepts that medicine has abandoned as it has advanced.

[Knight of L-sama]

It is well-known in Japan, and has nothing to do with throwing balls of energy, creating hurricanes, or poking things till they explode.

Street Fighter II, Dragonball, more wuxia movies than you can poke a stick at. Most of that stuff has some basis in old Chinese legends somewhere. Modern authors, movie makers and others just took ideas that were already there and ran with them.

[Bliss]

*shrugs* I know the Chinese still believe in using Qi to heal, it's what 'traditional Chinese medicine' is all about... balancing the Qi in your body via herbal medicine, accupuncture and the like... And you can use it as a diagnostic method, as the Cantonese call it, Da Mok, or feeling the flow of the Qi in your body.

[Pale Wolf]

Street Fighter II, Dragonball, more wuxia movies than you can poke a stick at. Most of that stuff has some basis in old Chinese legends somewhere. Modern authors, movie makers and others just took ideas that were already there and ran with them.

The latter has some association with the concept. The tossing of energy blasts as in the first two really doesn't. They just used the concept as an excuse to toss in pyrotechnics. Same as magic - the myths and ideas are pretty much never as flashy as the representations of magic you tend to see in anime like Slayers.

[Cheb]

how about this in healing Ranma and the others seem to be able to use their chi to heal them selves

Take the definition of Qi effects from Wikipedia and blow it to unreal proportions. You'll get Ranma.
Reading deeper into that page gives you an idea that there is no clear border between Ki and magic, because the real-world (so to speak) basis is very vague. I'd even dare to say that all Ranma techniques fit the domain [Spirit magic (aka Shamanism) -> Air] of the Slayers universe.
It's almost sure thing that Ki(Qi) and the "force" Jedi use are absolutely one and the same thing.
Do not forget also that using "Ki" is a great pun in Japanese, so of course we do see it in a comedy. I, personally, did try to translate directly from Japanese when I was making a Russian fansub for the episodes where Ranma &Ryouga learn their Ki attacks. I should say, there are a lot of "Ki"-based puns, including Nabiki flipping up Akane's skirt: "I just want to be sure who spoiled the air (Ki)" - after Ranma's umpteenth failed attempt to produce Shishi Hokou Dan.

[stratagemini]

Chi, is (according to Tai Chi) The energy that permeates all things, it's no so much external as it is omnipresent. It moves in spirals through and around the limbs flowing out from the hara (the belly where it's generated) and disperses into the earth through the feet. In spiralling it allows tai chi masters to become unmoveable and to put far more force into their strikes and redirect foes easier.
When we speak of Chi attacks in Tai chi it's using the power of your chi to do things normal humans can't do, like become immovable or send opponents flying with a feather light touch, or become nigh invulnerable and able to withstand having 2x4s swung at you and broken on you without noticing.
In Ranma 1/2 Ranma takes this a step further later on. There are infact myths of munks able to find support on a single twig in teh water with solely their chi, or ninja walking on water with only their chi (in reality they used a rather clever device called a water walker to achieve the effect).
In Ranma they exaggerate this to the extreme using Chi to allow people to Fly, or release attaks of concentrated Chi.
these two have a basis in martial arts myths. the Kiai or battle cry is supposed to be an emotion fueled attack to knock your opponents off balance with the power of your chi, though in this case Chi can also be said to represent concentrated Emotional power.
Chi deosn't really have a set definition. the best I've heard so far is that it "Allows the body to push past it's limits and in some cases shatter them." genma's Sen Ken schools use classic types of Chi manipulation, making your footfalls inaudible for instance, and almost fading from notice are both classic uses.
That Ranma has a Chi Attack is actually more based out of fighting games than martial arts. In traditional martial arts Chi is useful to improve your performace in various ways, and hinder your opponents performance.
I hope that helps.

[Bliss]

*grins* There's also the aura aspect, to fortify internal energy to wrap around the body as a protective layering... or at least that's what it's believed to happen in some cases of Shaolin, or the like, to concentrate the flow of energy into a certain part of the body to create a layer of protection...
There's also the idea of Qi as a way to determine power and used as a psychological attack. There are myths about being able to sense someone's strength by sensing the amount of 'Kill Intent'...*shrugs* Again, that's mostly a myth....
Qi for most people is like the yoga breathing/meditation exercises, rather than some sort of 'magic' to be utilized to accomplish the impossible.

[Tovath]

Wow I'm surpised at the response I got thank you every one

[Climhazard]

Most of that stuff has some basis in old Chinese legends somewhere.

Actually, how i can understand, most of stuff that NWC(and others) able to do, heavily based on Shugendo or, more precisely, on abilities of shugenja's. At least their abilities sound pretty similar... Shugenja supposedly able to manipulate their internal energy, possesed high physical strength, can jump very high(or even fly), shatter stone's by scream, and even can do stuff that sound very similar to Neko-ken. etc, etc, etc.