Density, Mass & Volume

Why do you think ice floats in water? Lets explore why!

Archimedes 287 B.C. – 212 B.C.

A little history… King Hieron II of Syracuse had given the goldsmith a particular amount of gold to melt down and make into a crown. When the crown was made and returned to the King, the King was suspicious that the goldsmith had stolen some of the gold and replaced it with an equal weight of silver. The king turned to Archimedes for help… Legend says that Archimedes discovered the principle of displacement while stepping into a full bath. He realized that the water that ran over equaled in volume the submerged part of his body. The legends goes further and tells that Archimedes was so excited with his discovery that he hopped out of the bath, and rushed naked into the street yelling triumphantly, "Eureka!" "Eureka!" (Greek word for 'I have found it!).

Mass Mass is the amount of matter, or stuff, that something is made of. ***Mass is always measured in grams (g)

***Volume is always measured milliliters (mL) or cm3 Volume is the amount of space that something occupies or the amount of space that something contains. ***Volume is always measured milliliters (mL) or cm3

Volume of Regular Shapes Volume = Length x Width x Height

Volume of Irregular Shapes Use displacement (the amount of water that is raised when a solid object is placed in the water)

How do you calculate water displacement for irregular objects? 23mL – 20mL = 3mL Amount you end with – Amount you start with = Volume of the object Volume of the object is 3 cm3

Density Density is the amount of matter (mass) in a given space (volume) ***Density is always measured in g/cm³

How do you calculate density?

To find density of an object you must know the volume and the mass of that object.

To find the density 1- Find the mass of the object 2- Find the volume of the object 3- Divide Density = Mass Volume

Problem 1 The mass of a silver bracelet is 48g, it occupies a volume of 4cm3, what is its density?

Problem 2 A 9g sample of a substance occupies a volume of 3cm³. What is its density?

Problem 3 A rectangular block of Lead (Pb) measures 2.0 cm X 3.0 cm X 4.0 cm. If the mass of the Pb block is 48g, find its density.

Problem 4 A cube of gold (Au), which has all equal sides, has a side length of 2.0cm. If the sample is found to have a mass of 88.0 g, find the density of Au.

Have you wondered why hot air balloons rise? When the air is heated, it becomes less dense until the balloon's total density is less than that of the atmosphere; A hot air balloon is literally floating on the denser, colder air. Why is cold air denser than hot air?

Do you know why volcanoes erupt? The main reason that magma rises to the surface to erupt at volcanoes is because it is less dense than the rocks that surround it.

A ship floating on water is a great illustration of the difference between mass and density. A ship must have a density of less than 1.0 g/cm3 (the density of water), or it will sink. Ships have a large mass, because they are made of steel, but because they have a large volume, their density is less than 1.0 g/cm3. If enough mass is added to them such that their density goes above 1.0 g/cm3, they will sink.