Density •describes how closely packed the particles are in a solid, liquid or gas. •amount of mass per unit volume. • All matter contains small particles called atoms. • The difference between the different states of matter is how the particles are arranged: in a solid – particles are tightly packed in a regular structure in a liquid – particles are tightly packed but free to move past each other in a gas – particles are spread out and move randomly Density also depends on the material. For example: A piece of iron with the same dimensions as a piece of aluminium will be heavier because the atoms are more closely packed. Calculating density •density (ρ) is measured in grams per cubic metre (g/m3) •mass (m) is measured in grams (g) •volume (v) is measured in cubic metres (m3) Mass -The amount of matter an object has. -Unit of measurement = -What tool do we use to find mass? Volume • If the object is a regular shape, the volume can be found by using a ruler and then using the equation: • Volume = length × width × height • If the object has an irregular shape, the volume can be measured using a displacement/eureka can. • The displacement can is filled with water below a narrow spout and allowed to drain until the water is level with the spout. Volume The quantity of space an object occupies. -Unit of measurement = so which one do you use when? -What tools can we use to find volume? Finding Volume of an Irregular Shaped Object (8Am) -Can’t use a ruler!!! -Find volume by water displacement method. -Volume of water with object – volume of water before object -Don’t forget to read the graduated cylinder from the bottom of the meniscus!!! What is the reading on this graduated cylinder? How about this one? Last one! What is the density of a material of 0.45 cubic metres (m3) if it has a mass of 0.2 kg? = 0.44 kg/m3 There are different ways to investigate density. In an experiment to determine density of liquids and solids, it is important to: • record the mass accurately • measure and observe the mass and the volume of the different objects • use appropriate apparatus and methods to measure volume and mass and use that to investigate density Note and make a point to remember : • Density of water = 1.0 g/cm3 OR 1.0 g/ml Errors when determining densities When taking measurements: 1)This the top pan balances used by different people may not be identically calibrated 2) resolution of the measuring cylinders may be different, causing different values for the volume to be recorded Why is Density Important? -Any ideas? -Consider 1 kg of iron and 1 kg of cotton…. -Every element has its own unique density. How could that help?
