 Let's assume you have bought some jewelry and want to know whether it is made of gold and is not fake. How can physics help you with this? First you have to weigh the jewelry and determine its mass, then you have to find out the volume V of the jewelry. To do this you use Archimedes principle. This states that the amount of water displaced is exactly equal to the volume of the immersed body. So take a measuring cup of water, throw in the jewelry and look at the milliliter scale to see how high the water has risen. Convert the value into cubic meters. Now the density, row of the jewelry material can be calculated. Simply divide the mass by the volume. The gold has a density of 19,300 kilograms per cubic meter. If you also get this value then the jewelry is made of real gold.