The piano (or whatever) would only be accelerating due to gravity if it were going downhill in a sufficiently steep manner. Don't think there are many hills in a starship.
Tell that to Joachim
Any object shaken loose from the ceiling of the bridge (or the cargo bay or the engine room) will probably accelerate away from the wall at one or two meters per second tops, depending on what sort of force dislodged it in the first place. A FALLING object will hit the ground at five or six times that speed and, depending on its mass, will flatten whoever it lands on since the downward force is constant.
The same object tumbling through the bridge could be deflected with one hand and, if necessary, secured to the floor with a single strip of duct tape until it can be disposed of.
Gravity only accelerates in one direction: down.
And zero gravity accelerates in NO direction, ever. That simply means that unless the ship suffers the total failure of its inertial dampeners (in which case your crew is screwed with or without gravity) the ship isn't going to move much unless something hits it. Thus you're able to prevent falling injuries
, crushing injuries
, and other shenanigans
that goes on whenever the ship is hit by something.
Also, the ground makes a whole lot more friction than air (or vacuum!)
Which is part of the problem, you see, as nine times out of ten the GROUND is the thing those redshirts are crashing into when the ship gets hit. When your unlucky tactical officer gets blown into the air from an exploding console, he isn't going to get a concussion or a broken arm from flipping over the railing and landing on his head. He might actually CATCH the railing and climb back into what's left of his console (which, thanks to the lack of oxygen, is no longer on fire).