Ok, I'm about halfway through this "novella", and while I find the story itself very pertinent, I still haven't seen it define what a gravity knife actually is -- what differentiates it from other classes of knives. Admittedly, I've taken to half skimming, as I didn't intend to make a significant time investment in learning this.

Here are some pertinent -- essential -- details, from mid-way through the article. First, I guess I should add that the article talks earlier about the problem of knives being perhaps deliberately mis-classified as gravity knives (without actually defining this).

Gravity-knife arrests may be popular for another reason. Most, like Neal’s, result from simple observation of a “pocket clip,” often readily visible. All officers need to do is keep their eyes peeled, and they can add another misdemeanor to their tally — or, if they’re lucky, a felony.

Matt Galluzzo, a former assistant district attorney in Manhattan, now a defense attorney in private practice, says that for many officers, a gravity-knife arrest is simply a hard collar to pass up. “You don’t have to fight the guy, you don’t have to chase him,” Galluzzo says. “It’s an easy way to make an arrest. And they’re under pressure to make arrests.” A poster on Officer.com, a verified online message board for law enforcement officers, put it bluntly in 2013 when he advised a rookie to be on the lookout for “GKs”: “make sure they have a prior conviction so you can bump it up to that felony!!!”

Most of the D.A.s in the state “have never prosecuted a gravity-knife case, or haven’t prosecuted one in 30 years,” according to a spokesperson for the District Attorneys Association of the State of New York. Even just beyond the city limits, gravity-knife prosecutions are exceedingly rare. While the population of the Bronx is roughly equal to that of Suffolk County on Long Island, the Bronx prosecuted more than 10 times as many likely cases in 2013 as its counterpart across the water.

Even worse, critics charge, is that officials have prosecuted knife users aggressively while doing little to address the source of those same knives, which are sold openly at reputable retailers all over the city. New York State assemblyman Dan Quart, a Democrat from Manhattan, says there’s an obvious contradiction at play: “You can walk in and purchase one of these knives over the counter,” he says, “and then walk out and get arrested.”...

The racial breakdown of stops is also striking. Of the thousands of arrests that resulted from stop-and-frisk encounters, 86 percent of the total involved black or Hispanic suspects. And a Voice analysis also shows that white suspects are significantly more likely to be let go, even when they’re caught carrying knives. Only 35 percent of white suspects found with knives — virtually any of which might meet the NYPD’s ecumenical definition — are arrested, while 56 percent of black and Hispanic suspects are ultimately booked.

Ah, and finally, a definition of what a gravity knife is:

The original gravity knife — the type legislators targeted when they banned them half a century ago — bears no resemblance to the kind that landed Richard Neal and thousands of others in jail over the last decade. Developed by the German military for use by paratroopers during World War II, the idea behind a gravity knife was simple: An unlucky parachutist who found himself in a tight spot — tangled in a tree, for example — would be able to access the knife even with injuries or limited mobility. Simply press a button and the blade would literally fall out of the handle and lock in place...

The legislature didn’t target gravity knives at the time — they were still rarely seen in the U.S. But after switchblade bans went into effect, the knife industry saw an opportunity. Even though they were nearly identical in design, gravity knives lacked a spring, a key characteristic of the newly illegal switchblades. So manufacturers stuck with warehouses full of worthless knives simply removed the springs and went on selling, calling the new products “gravity knives.”