When Gandalf plummeted down the abyss in Moria at the beginning of TT, I was disgusted by the bad physics there.
Seemingly, a wizard in flowing robes experience a greater acceleration of gravity (or less air resistance?) than a sword!
Possibly, terminal velocities are reached faster in Middle-Earth, and thus, being more massive, Gandalf is able to overtake his sword.
However, even though the Balrog's wings seemed largely ineffectual, they're still huge, creating a lot of air resistance, and the sword ought to have passed beyond the
balrog prior to Gandalf overtaking it.
There does, of course, exist the slim possibility of Gandalf being able to manipulate the local gravitational fields a bit (him being a wizard and all), but if that were the case, PJ
really should have shown him chanting as he fell..(or perhaps not

)