Some substances such as wood and cork float in water. Other substances such as iron and concrete sink. Why? It all has to do with density, explains 3-2-1- Contact magazine.
To measure the density of an object, you have to compare its weight with its size. But what if one is iron and the other is Styrofoam? The iron cube weighs more. That's because iron has more matter packed into it. Iron is more dense.Substances less dense than water - such as wood - float in water. Substances more dense than water - such as gold - sink.
By itself, size has nothing to do with whether an object sinks or floats. If the substance is less dense than water, it will float no matter how big it is. So a tiny block of wood will float in your tub. And a huge log of wood will float on a lake.