iron is 7.9 times greater than water
No, a piece of iron will sink in water because its density is greater than that of water.
The density of iron is higher than that of water, so the iron nail sinks in water due to gravity pulling it downwards. The weight of the iron nail is greater than the buoyant force acting on it from the water, causing it to sink.
Iron has a greater density.
Earth has an even greater density than Mercury. Presumably, planets a core of dense materials (for example, the density of iron is 8 times that of water), which compensates a lighter (less dense) crust.
No, even if the density of the iron is less than water, the density of the iron box as a whole would still be greater than water, making it sink. Density is determined by the total mass of an object divided by its total volume, not just the material it is made of.
A block of iron will float in mercury due to the higher density of iron compared to mercury. In water, the iron block will sink because the density of iron is higher than that of water. The buoyant force acting on the iron block is determined by the density of the surrounding fluid.
Many metals such as iron, lead, and gold have a greater density than water and will sink when placed in water. Other examples include platinum, mercury, and uranium.
The density of iron is larger than water because iron atoms are more tightly packed together, resulting in a greater mass per unit volume compared to water. This is due to the difference in atomic structure and mass between iron and water molecules.
The ships are not made of solid iron. They contain much empty space where the cargo and or passengers go. So the overall density of a ship: its TOTAL mass divided by its TOTAL volume is less than that of water.
Iron.
The iron nail sinks in water because its density is greater than that of water. The katori floats because its shape and material make it less dense than water, allowing it to displace enough water to generate a buoyant force greater than its weight.
I am assuming that you mean float (or sink) rather than "slow". Knowledge of density will not help - unless the object is compact. The density of iron is greater than that of water but ships made of iron will float.