It is all to do with the density. Water has a density of 1g/cm^3 (1 gram per centimetre cubed). Anything that has a density of less than this will float in water, but anything that has a density greater than this will sink.
An object will float if it is less dense than the water (or other liquid). If it is denser than the water, it sinks.
If a block of wood floats in water, it means that the density of the wood is less than the density of water. This is because objects with a lower density than water will float, while objects with a higher density will sink.
objects that are less dense float to the top.
It's far from clear what the actual question is. Some objects float in both salt and fresh water, some objects float in neither, and some objects float in one but not the other. Any object that floats in fresh water will float in salt water, but the reverse is not true.
Mass b > mass a
Styrofoam is lighter than water, so it floats. In nature, heavy objects are more effected by gravity, so they are forced down.
Iron sinks in water because it is denser than water. However, iron is able to float on the surface of water in certain conditions (such as with a carefully placed thin piece of iron) due to surface tension and the water's ability to hold up lighter objects like certain metals.
when some thing is less dense than the liquid it floats
less than water different objects have varying densities
You can tell that it is less dense than water which has a density of 1 cc
Objects that are less dense than water will float, while objects that are denser than water will sink. For example, wood, plastic, and cork typically float in water, while metals like lead and iron sink. The shape and size of an object can also affect whether it floats or sinks.
CO2 floats because its density is less then water. Anything will float if its density is less then water. That is; when a certain volume of CO2 (or anything else) weighs less then the same volume of water.