In a vacuum room, where is no air resistance, the bowling ball will have the same acceleration as the feather. That means to say that both will have the same speed at any time and reach the floor at the same time.
Density is the mass per unit volume.
Common units for density are g/cm3 or kg/m3. SI unit is kg/m3.
Density of a pure substance is fixed, regardless of it’s size!
Floating and Sinking
A denser (heavier) substance will sink in liquid which is less denser (lighter).
A less dense substance will float in a liquid which is denser.
If substance has the same density as the liquid, it will be suspended in the liquid.