If an object is less dense than that of a fluid, then why doesn't it float completely over the fluid level? Why does some part of the object remain submerged in it? Can there be an object that can float 100% on water? (If this involves surface tension (Is that what it's called?), please clear that up, too. Don't understand that concept yet. But it would be better if your answer didn't include that.)
Fluid Density – Why Doesn’t an Object with Less Density Than a Fluid Float 100% Above the Fluid Level?
densityfluid-staticsforcesfree-body-diagrampressure
Best Answer
The buoyant force on an object is equal to the weight of the fluid that the object displaces. If you hold an object just at a fluid surface, there is gravity acting on it, which is opposed by the force that you have to apply to the object to hold it stationary, but there is no buoyant force on it because it hasn't displaced any fluid. As you lower the object into a fluid, the force of gravity pulling it down is constant but the buoyant force on the object increases as it displaces more fluid. At some point, a floating object will displace enough fluid for the buoyant force pushing the object up to equal the force of gravity pulling it down, and the object will float with some portion of the object above the fluid.
Regarding this phenomenon, density is a bit of a "red herring". While it is true that objects that are less dense than a given fluid will float in the fluid, it is also true that objects that are more dense than a fluid can float in the fluid. For a cargo ship at sea, the hull of the ship is made of steel, which is approximately 7 times as dense as sea water, yet the ship still floats because the ship's hull has a shape that allows it to displace its weight of water before it sinks in that water.