Density

Which weighs more? Which one of these weighs more??? A kg of bricks or a kg of feathers? Both of the objects are 1 kg… so they both weight the same. So why do we want to say bricks???? A kg of bricks may not weigh more, but it does have a higher density!!!

What is density? Density is the amount of mass an object has per unit of volume. How tightly or loosely packed the molecules in a substance are. All substances have densities, solids liquids and gases.

Differences in Densities Two objects with the same volume and different masses will have different densities. Take a look at the picture below and decide which object is more dense.

Differences in Densities Which one of these boxes is more dense??? Box B… Why? The same amount of matter (mass) is packed into a smaller space (volume)

What about liquids? Differences in densities can be seen in liquids to. When liquids of different densities are mixed together, the denser liquids will sink below the less dense liquids. Oil, least dense. Water. Syrup, most dense.

Another Example

What about Solids IN Liquids? If a solid is placed in a liquid it will either sink or float. Solids with a higher density than the liquid they’re placed in will sink. Solids with a lower density than the liquid they’re placed in will float.

Examples? Wood will float in water, so wood is less dense than water. A block of lead will sink in water, so lead is more dense than water. Lead is less dense than mercury. So….

Lead will FLOAT in Mercury!

Ice in Water? Which has a higher density? Ice or water? Ice floats in water, so water must have the higher density… but why? Water EXPANDS as it freezes!!

Do Now Define Density Describe what happened to a solid with a low density when it is placed in a liquid with a high density

To calculate Density: Equation: Mass (g): Volume (cm3): Triple Beam Balance Volume (cm3): Measure (L x W x H) Water Displacement (Graduated Cylinder)

Density’s Label Mass is always measured in grams Volume of Liquids and Gases are measured in milliliters Volumes of Solids are measured in cm3

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

Example 1 What is the Density of the following Solid Object? MASS cm MASS 160.0 g W = 2.0 cm L = 4.0 cm

Answer (Example #1) V = 16.0 cm3 = 10.0 g/cm3 Mass = 160.0 g Volume = L x W x H V = (2.0 cm) x (4.0 cm) x (2.0 cm) V = 16.0 cm3 160.0 g D = = 10.0 g/cm3 16.0 cm3

Do Now Calculate the density of an object with a mass of 47 g and a volume of 73 cm3 Calculate the mass of an object with a volume of 38 cm3 and a density of 1.4 g/cm3 Calculate the volume of an object with a mass of 25 g and a density of 2.8 g/cm3

WHICH HAS A GREATER DENSITY? Size and Density How will an object’s density change if it is cut into two or more pieces? Mass = 16.0 g Volume = 4.0 cm3 Density = ________ Mass = 4.0 g Volume = 1.0 cm3 Density = ________ 4.0 g/cm3 4.0 g/cm3 WHICH HAS A GREATER DENSITY? = 1g particle = 1cm3 THEY ARE THE SAME! 19

Factors Affecting Density Temperature When temperature increases, objects expand, causing the density to decrease. Pressure When pressure increases, objects compress, causing the density to increase. 20

Temperature and Density Heat Added Object Expands Temp Density Indirect RELATIONSHIP: As temperature INCREASES, density DECREASES 21

As pressure INCREASES, density INCREASES Pressure and Density Pressure Added Object Compresses Press Density Direct RELATIONSHIP: As pressure INCREASES, density INCREASES 22