Density

Which is heavier? Steel or wood? The density of a substance tells you the mass of a particular volume of the substance

The standard unit of mass is the Kilogram Kg The standard unit of volume is the metre-cubed Unit of density is kilogram per metre-cubed It is more usually written as

Water will always have a density of Density depends on the substance and what it is made of rather than how big it is.

The story of Archimedes and the Crown Archimedes was asked by the king to solve a problem for him. He wanted to know if his crown was made of pure gold. Archimedes knew that he could prove that the crown was made of pure gold by finding its density. If the crown contained silver as well as gold it would be less dense than pure gold. He had to find a way to find the volume of the crown! When he climbed into the bath he noticed the level of the water rising so he realised he could use this method to find the density of the crown. He jumped out of the bath and shouted EUREKA!

Flotation – Whether an object floats or sinks Flotation – Whether an object floats or sinks. Fluid – A liquid or a gas. E.g. water or air Something will float in a fluid if it is less dense than that fluid. Something will sink in a fluid if it is more dense than that fluid. Eg. A stone in water. The coin is less dense than the mercury because it floats.

A ship floats in water because it contains a lot of air A ship floats in water because it contains a lot of air. If it springs a leak water will rush into the ship and it will sink. Flotation increases if the density of the fluid increases. Eg. There is a high concentration of salt in the Dead Sea.

It is not just solids that float. Liquids can float on other liquids It is not just solids that float. Liquids can float on other liquids. Why does oil float on water?