“Norbit” may be billed as a comedy, but absent of laughs or surprises, it’s essentially a physics experiment about mass in motion. Encased in a blobby fatsuit as the movie’s Brobdingnagian female, Eddie Murphy demonstrates the displacement of (a lot of ) water, sudden impact with smaller objects (i.e., Norbit), and the bulging-sagging coefficient. Again and again and again. “Make it big” goes one comedy axiom, ground here into a fine powder.

The butt of the movie’s joke, Rasputia, is actually its bully. Though reaching new heights of fat-bashing, “Norbit” taps the venerable comic teaming of a domineering shrew and a henpecked hubby, both of whom are played by Mr. Murphy. Our afroed, bespectacled milquetoast Norbit, introduced as a vulnerable orphan, was all too eager to marry someone big and strong for protection.

Some years on, rivalry brews when Norbit’s childhood sweetheart from back at the orphanage, Kate (Thandie Newton), returns to town. The gold-hearted, bony woman is in her own dubious relationship, putting misguided trust in her shifty fiancé Deion (a weary-looking Cuba Gooding Jr.). Like Rasputia’s three huge brothers, who run a protection racket in town, Deion has an eye on the orphanage’s valuable land. Meanwhile, Norbit pines anew for Kate. Cowering and squashing ensue.

More interesting than the plot is how Mr. Murphy’s customary multiple-role, partly improvised performance gives “Norbit,” like his other films, a glimpse into the actor’s psyche. Mr. Murphy is an actor who churns through and reworks old bits and fragments of personas, notably his Jekyll-and-Hyde turn in 1996’s “The Nutty Professor,” in which Mr. Murphy ceremonially sacrificed his 1980s devilish fast-talker persona in the person of Buddy Love. Swapped in was the tamer, family-friendly Sherman Klump, who not only won out at the end of “Nutty Professor,” but pushed Mr. Murphy into family territory (“Doctor Doolittle,” “Daddy Day Care,”) that nearly wrecked his career.

Norbit follows as another negation of that blue-streak cool — a kindly dork who feels the tug of true love. Scheming, preening, and rolling, Rasputia is the old Murphy attitude made grotesquely manifest, in perpetual one-sided battle with her meek marital counterpart, and perhaps a purge of Mr. Murphy’s recent family fare.

But one despairs a little when examining this particular instance of Mr. Murphy’s vaudeville auteurism, a practice that long ago crossed from obsessive to unnerving. What to make of an actor who, by portraying a couple, is therefore playing at being carnally involved with himself? The ultimate expression of vapid, pointless comedy, or a narcissist’s cry for help?

Whatever the case, Mr. Murphy squanders his talents again in a slapdash movie that looks precut into preview trailers and that peddles Rasputia’s tag-line (“How you doin’?”) as insistently as a gimmicky sitcom. Sporadic worthy bits, like Norbit’s enraged little nerd-outs and Rasputia’s halfheard impromptu elaborations on her lines, are a treat, but they lie buried in cruddily shot scenes on town-square and house sets that look like an afterthought.

Sadly, that ingenious fat suit has the effect of obscuring the skill in Mr. Murphy’s physical comedy. Not that the character allows much expression other than orneriness and momentary shock at just how much she will have to beat Norbit for his latest screw up. The less mention made of a third, less advertised character — the crude but caring Chinese head of Norbit’s childhood orphanage (also a Szechuan restaurant) — the better. Rasputia may have the threadbare excuse of a tradition of drag that long precedes Mr. Murphy (or Martin Lawrence), but the ethnic impersonation known as “Wong” never sits well.

Ms. Newton, playing the gullible sweetheart who inevitably misunderstands Norbit’s intentions at some point, is regrettably asked to discard all traces of her flair for feistiness. Plainly, nothing must stand in the way of the freakshow main event. Even Rasputia’s three brothers, two of them former football players, make little impression with their Popeye physiques. One exception, woefully underused, is a pair of precisely tailored town pimps (Eddie Griffin and Katt Williams) sympathetic to the wimp’s plight, who dispense a confidently loony patter.

Director Brian Robbins most recently brought a breezy touch to the insipid Tim Allen vehicle “Shaggy Dog,” which is no mean feat (though still no good movie). But here Mr. Murphy must have taken over completely. “Norbit” feels like a film in which every day, after hours and hours of makeup, there simply was no time left for anything else.