# TOC: 9/26/2013 Density Starter:

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TOC: 9/26/2013 Density Starter:
Review your definition of density and rewrite it in your own words.

Practice : What is density?
Density is a comparison of how much matter there is in a certain amount of space. Each substance has its own unique density, based on the size of particles and how many particles can “fit into” a given space.

Which one is more dense? WHY???
It has more particles in the same amount of space

Which one is more dense? Now which one is more dense? WHY???
It has less space for the same number of particles

How do you calculate density?
Density = mass OR mass ÷ volume. volume M = mass D = density V = volume Density = mass volume Mass = density x volume Volume = mass density

Density can also be described as the amount of mass contained in a given volume.
Units used for a solid: g/cm3 Units used for a liquid: g/mL

Mass(g): the amount of matter in a substance. (Then what is weight?)
Weight(g): The gravitational pull on an object. You would weight less on the moon, but your mass would be the same. Volume(cm3 or L): the amount of space an object takes up

Liquid Layers If you pour together liquids that don’t mix and have different densities, they will form liquid layers. The liquid with the highest density will be on the bottom. The liquid with the lowest density will be on the top.

Liquid Layers Which layer has the highest density?
Which layer has the lowest density? Imagine that the liquids have the following densities: 10g/cm3. 3g/cm3. 6g/cm3. 5g/cm3. Which number would go with which layer?

Water The density of water is 1.0g/mL
If something is more dense than water, it will sink. If something is less dense than water, it will float. Generally, liquids are less dense than solids and gases are less dense than liquids.

Application: Let’s try a density problem together
Example 1: Frank has a paper clip. It has a mass of 9g and a volume of 3cm3. What is its density? D = m v D = 9g 3 cm3 D = 3 g/cm3

Work on these problems with your neighbor.
Example 2: Jack has a rock. The rock has a mass of 6g and a volume of 3cm3. What is the density of the rock? Example 3: Jill has a gel pen. The gel pen has a mass of 8g and a volume of 2cm3. What is the density of the gel pen?

Answers Example 2 Example 3 D = 6 g D = 8 g 3 cm3 2 cm3 D = 2 g/cm3

Mass, Volume, or Density? Example 4: If 25 mL of oil has a density of 2 g/mL, what is its mass? Mass = D x v M = 2 g/mL x 25 mL M= 50 g

Mass, Volume, or Density? Example 5: If a pencil weighs 4 grams and has a density of 2 g/cm3, what is its volume? Volume = m D V = 4 g 2 g/cm3 V = 2 cm3

Connection Practice Time!!!
Complete the worksheet: Mass, Volume, or Density? Show the formula Show what numbers (with units) you are using give your final answer (WITH UNITS) 16

Exit What is the formula for density? D=m÷v
What are the units for the density of a solid? g/cm3 What happens if you pour together liquids that have different densities? They form liquid layers

And the final two… What can you say about the density of the top layer? It is the lowest In general, what are less dense than liquids? gases