Customers look over Apple's iPad 2 at the Apple store in San Francisco on Friday. Apple may sell 600,000 of the second version of the iPad when it debuts this weekend, extending the device's lead in a crowding market. (David Paul Morris/BLOOMBERG)

Across America on Friday, people lined up for blocks to buy an incremental update to an established product. In the gadget market, that’s not ordinarily rational behavior.

But Apple’s iPad and the iPad 2 that arrived in stores Friday are not ordinary gadgets.

The first woke up a tablet-computing market that had been occupied only by heavy, slow devices running versions of Microsoft’s Windows operating system. The second, priced at $499 and up like the first, doesn’t do all that much more: It’s a lot thinner, a little lighter, has a faster processor and adds two cameras.

But maybe it doesn’t have to. A survey for ChangeWave Research conducted in February — well before Apple chief executive Steve Jobs introduced the iPad 2 in San Francisco on March 2 — found that 82 percent of would-be tablet buyers had an iPad on their shopping lists.

Going by a first glance at an iPad 2 loaned by Apple — a high-end, $829 WiFi-plus-3G model compatible with AT&T’s network, loaded with 64 gigabytes of memory — this device’s immediate contributions will be bringing video calling to more places and slightly lightening travelers’ luggage.

The iPad 2’s front and back cameras support Apple’s FaceTime software, which provides convenient video calling — over WiFi only, not 3G — to friends using a recent Mac, an iPhone 4 or the current iPod touch. Fortunately, FaceTime isn’t the only option. Skype’s Internet-calling application also worked properly with the iPad 2’s cameras, although the program (which Skype has yet to tune up for the iPad) only occupied a small chunk of the iPad 2’s 9.7-inch screen most of the time.

These cameras can take still photos as well but should be used for that purpose only in an emergency: Their grainy, low-resolution pictures were little better than the output of the first generation of cameraphones.

(If you suspect that Apple won’t offer a flash or higher resolutions — the front camera records 640 by 480 pixel shots, the back 720 by 960 — until it can build those features into an iPad 3 that it will introduce after months of anticipation, you’re wising up to the ways of this company.)

The iPad 2’s thinner profile is even more obvious. Apple touts it as being a third thinner than its predecessor, at just over a third of an inch thick. And at 11 / 3 pounds, it’s notably lighter, too.

The standard case Apple sells, a nifty, folding, magnetically attached screen protector called the Smart Cover, makes the iPad 2 seem even thinner next to an iPad clad in Apple’s older, thicker case.

Inside the iPad 2, Apple has packed in a battery that it says delivers the same 10 hours of nonstop Web use as the first model, plus a significantly faster processor called the A5.

This new chip’s power did not seem obvious in everyday browsing or even when playing around with older applications such as Google Earth. (Web browsing on the iPad continues to exclude video and animations in Adobe Flash, making many sites incomplete and a few unusable.) But applications written with the iPad 2 in mind suggest some interesting possibilities. Apple’s $4.99 GarageBand, for example, lets even the musically inept put on a passable demonstration of musicianship with “smart instruments” that make strumming a few chords on an onscreen guitar no trickier than the beginner level of Guitar Hero.

There’s no reason other tablet computers couldn’t learn Apple’s tricks. Current and upcoming tablets from companies such as Motorola and Research In Motion have fast processors, too. Many also offer features that Apple seems to have ruled out on the iPad, such an SD Card slot to allow additional memory and easy file transfer. Competing tablet operating systems such as Google’s Android also make it easier to switch among multiple applications at once, and they don’t subject developers to Apple’s restrictive stewardship of its App Store.

Yet none of these rival tablets, such as Samsung’s Galaxy Tab or Motorola’s Xoom, seems to have left much of a dent in the iPad’s shiny exterior.

Price is one reason. At $499 for a WiFi model with 16 GB of memory, the basic iPad 2, which is more than enough tablet for typical home use, beats the price of most competing name-brand models. (Barnes & Noble’s NookColor costs only $249, but that does little more than display e-books and browse the Web.)

If rivals can’t come under that just-under-$500 figure, they’re going to have to beat Apple in terms of elegance and ease of use. But to judge from the sluggish, overpriced Tab and the embarrassingly incomplete Xoom, that’s a lesson they have yet to learn. One of these companies will figure that out before long — but until then, Apple might have this market to itself for a little longer.