Walking round Tate Modern the other day, looking at its rearranged galleries, I found myself obsessed with hanging - not in the curatorial sense of hang (to arrange paintings and sculptures in a gallery according to historical and aesthetic principles), but in the more ordinary sense of suspending something. Suddenly there seemed to be works hanging everywhere. In one room, Juan Muñoz's Hanging Figure apes the pose in Degas' great painting Miss LaLa at the Cirque Fernando, swaying gently in the air-conditioning about 10 feet above your head. In another room, Louise Bourgeois' sculpture Fillette also dangles from the ceiling - a phallic joint of meat, weighed down by its testicular ball joints. There are Calders here, too, and, in a large gallery devoted to minimalism, Robert Morris's Untitled - a strange fibreglass square suspended on four slender wires, like a kiosk selling vacancy. And upstairs, in a space dedicated to recent acquisitions, Pae White's Morceau Accrochant floats in the air, a precisely marshalled constellation of multicoloured discs that owes rather more than it ought, to my eyes, to Cornelia Parker's work.
I blame Sam Taylor-Wood for this lapse into tunnel vision. Last week I went to see her retrospective show at the Baltic in Gateshead, and spent most of the time in front of two series of photographs, which appear to show the artist magically suspended in space. In both cases Taylor-Wood has digitally erased the harness and wires that held her in place, so that the resulting image appears to show an uncanny levitation. If this was just a conjuring trick with gravity it wouldn't be terribly interesting, but what makes both series so compelling is the uncertainty of Taylor-Wood's postures, which place her ambiguously between floating and falling. In some images she seems to reach pleadingly towards the ground, as if she longs to recover her footing. In others she reclines on the air as if it were a hammock. It isn't easy to say whether she's unconscious or languorous, hung out to dry or flying - and all of those ambiguities are emphasised by Bram Stoker's Chair, a series in which she appears to rest on a precariously balanced chair that, unlike her body, casts no shadow.
It doesn't exactly hurt the spectator's pleasure in these pictures that she has an attractive body, though I can't help feeling that it hurts the art a little, giving a high-fashion gloss to images that are already in danger of looking too beautiful. It could easily distract you from the pathos of these pictures, and the strange, mixed feelings that suspension conjures up, even when the means of suspension has been airbrushed out of the record. What they do - by ostentatiously pretending that gravity has relaxed its hold on the body - is make you feel simultaneously wistful at its dull grip and a little grateful that it keeps us grounded so effectively.
Those sensations are always slightly different when the wires are visible, I think, even if they are related. Alexander Calder's interest in mobiles grew out of a fascination with circuses and - like Degas' picture of Miss LaLa - they key into a longing that gravity might possibly be transcended. Unusually - because of the lateral struts of many of his mobiles - they are reasonably successful at making you forget the inherent peril of most hanging works. Similarly, Parker's floating sculptures - perfectly aligned on an invisible plane beneath very fine metal wires - give the sensation of objects buoyed up by some invisible medium rather than vulnerably poised over a void. In both cases the wires are a means to an end, and we mentally push them into the background.
But in most hanging sculptures the wire is where much of the tension - rather literally - is concentrated. The prospective future of most hanging sculptures is downwards. We know that their destiny is to fall and that the wire is the only thing preventing them. So while we feel that a free-standing sculpture is somehow where it wants to be, a hanging sculpture always carries the sense that its place is provisional.
We might imagine that it fears the fall or yearns for it, but there is always something precarious about its condition. Bourgeois' Fillette and Muñoz's Hanging Man both look as if they are undergoing some kind of torture, and yet it's an ordeal that might easily count as a kind of rescue. How can we tell that they're not being prevented from falling towards something worse? What you can say for sure is that they have a way of reminding you of the weight of the world.