What is Density

What does it mean to be dense? Example: Think about Population Density. Two Countries have the same number of people living them. Which one is more densely populated?

Country “A” vs. Country “B”

What does it mean to be dense? Example: Two Countries are the exact same size. Which one is more densely populated?

Country “A” vs. Country “B”

Population Density vs. Density Population Density is a measure of the amount of people in an amount of land. Density is a measure of the amount of matter in an amount of space.

Density is a Derived Unit Which means it is: A Calculated measurement (NOT a Pure measurement) that depends on… The amount of matter in an object, which is called MASS. The Amount of Space occupied by an object, which is called VOLUME.

So what is density? A material's density is defined as its mass per unit volume. It is, essentially, a measurement of how much mass would be in EACH cm3 or ml of the object.

The object to the below has a MASS of 8.25 ounces Now remove the RED block from the object. The object to the right has a VOLUME of 11 Blocks That means the DENSITY of the object is 0.75 ounces per block What’s the MASS of the RED block? What if we took a BLUE one instead? What would be the MASS of the BLUE block? 0.75 ounces 0.75 ounces

Every object around us is made of Molecules. Different types of molecules can have different masses and different sizes There is little or no space between the molecules of objects. (The molecules are always touching) By changing the number or type of molecules in an object you can change the density of the object.

Imagine that a Beach ball represents a molecule Imagine that a Beach ball represents a molecule. The size of the beach ball can change depending on how much force is applied to it. To understand what is happening inside an object: imagine that we fill the entire classroom with beach balls (from wall to wall – floor to ceiling) Is it possible to make this “object” more dense by adding another beach ball?

YES. Since the walls give a little, we can force one or two more beach balls into the same space. This is also true of molecules Is there another way to make this more dense?

To calculate Density: MASS of the Object D = Volume of the Object

Notice that neither label will cancel out. So both must be kept. To calculate Density: Example: 1) Mass = 4.50 g 2) Volume = 80.0 ml STEP 1 = Mass Volume Notice that neither label will cancel out. So both must be kept. 4.50 g Step 2 = = 0.056 g/ml 80.0 ml

1 ml of Liquid will fit into a cube 1cm x 1cm x 1cm (1 ml = 1 cm3) Density’s Label Mass is always measured in grams Volume of Liquids and Gases are measured in Milliliters Volume of Solids are measured in cm3 This means: 1 ml of Liquid will fit into a cube 1cm x 1cm x 1cm (1 ml = 1 cm3)

Density’s Label Density of Liquids or Gases: g/ml Density of Solids: g/cm3

Use the Scale How to measure Mass? For Liquids and Gases you will need to subtract the mass of the container

How to measure Volume? Cubes: V = L x W x H Cylinders: V = x r2 x H π Liquids: Use the GRADUATED CYLINDER. Solids: Use Displacement (Direct or Overflow) Use volume formulas Cubes: V = L x W x H Cylinders: V = x r2 x H π

Example 1 What is the Density of the following Solid Object? MASS cm MASS 150.00 g W = 2.00 cm L = 2.45 cm

Answer (Example #1) V = 13.48 cm3 M d = = = 11.13 g/cm3 V STEP ONE Mass = 150.00 g Volume = L x W x H STEP TWO V = (2.45 cm) x (2.00 cm) x (2.75 cm) STEP THREE V = 13.48 cm3 150.00 g M d = = = 11.13 g/cm3 V 13.48 cm3

Example 2 What is the Density of the following Solid Object? D = 6.00 cm H = 8.00 cm r = ½ of D MASS 175 g

Answer (Example #2) V = 226.08 cm3 M d = = = 0.774 g/cm3 V STEP ONE Mass = 175 g Volume = π x r2 x H STEP TWO V = (3.14)x (3.00) x cm (3.00) x cm (8.00) cm STEP THREE V = 226.08 cm3 175 g M d = = = 0.774 g/cm3 V 226.08 cm3

Example 3 What is the Density of the following Irregular Object? MASS of Object = 54.00 g Volume of Overflowed H2O = 22.7 ml

Answer (Example #3) V = 22.7 cm3 M d = = = 2.38 g/cm3 V Mass = 54.00 g Volume = Volume of Overflowed H2O One ml = One cm3 Since the OBJECT is SOLID use this Label V = 22.7 cm3 54.00 g M d = = = 2.38 g/cm3 V 22.7 cm3

Volume of Displaced H2O = 5.0 ml Example 4 What is the Density of the following Irregular Object? MASS of Object = 8.25 g Volume of Displaced H2O = 5.0 ml Volume Before = 7.5 ml Volume After = 12.5 ml

Answer (Example #4) V = 5.0 cm3 M d = = = 1.65 g/cm3 V Mass = 8.25 g Volume = Volume of Displaced H2O One ml = One cm3 Since the OBJECT is SOLID use this Label V = 5.0 cm3 8.25 g M d = = = 1.65 g/cm3 V 5.0 cm3