How to find Density

Presented by…Your favorite teacher

Linear measurement (How to measure a line using

metrics)• What tool?

Meter stick or metric ruler

• What unit? Meter (m)

We usually use centimeters (cm) for things that will fit on our desk.

• For example: The length of the cell phone is about 8cm.

Mass…the amount of matter in an object

• What tool? Triple Beam Balance

• What unit? grams (g)

It’s a fact…

• Weight will change according to how much gravity is pulling down on you.

• Weight will change when an object moves into outer space.

• Weight and mass are two different things.

Finding the volume of a regularly shaped object, such as a box.

What tool?

Metric Ruler

Formula? V = L x W x H

What unit? •m3 for something large, like the gray cabinet in the classroom. •cm3 for something small, like the volume of a building block.

What is density?• Density is a comparison of how much

matter there is in a certain amount of space.

• If we calculate the density of these cubes, we can compare how much mass each cube has per cubic centimeter. That will tell us which cube is more dense.

Which one is more dense?

• Demonstration: People standing in a square

• How about this: Which square is more dense?

Which one is more dense?

• Now which one is more dense?

What is the formula for density?

• Density = mass OR mass ÷ volume.

volume

• Units for density: g/cm3

• Why are these the units for density? In our classroom, we usually calculate density in g/cm3 (This is because our triple beam balances only measure in grams, so we usually find the density of small things.)

• Does the unit really matter? YES!!!

• Match the illustration with the correct unit.

8 cm

8 cm2

8 cm3

•Answers:

8 cm3

8 cm2

8 cm

Let’s try a density problem together

• Frank has a big paper clip. It has a mass of 9g and a volume of 3cm3. What is its density?

Answer: 9g ÷ 3cm3 = 3 g/cm3

• Frank also has an eraser. It has a mass of 6g, and a volume of 3cm3. What is its density?Answer: 6g ÷ 3cm3 = 2 g/cm3

Work on these problems with your neighbor.

Jack has a rock. The rock has a mass of 3g and a volume of 15cm3. What is the density of the rock?

0.2 g/cm3

• A block has a length of 3.1cm, a width of 3.1cm, and a height of 6.2cm.

• It has a mass of 238g.

What is the box’s density?A: 3.99 g/cm3

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• Check out this picture from

your book. 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?

Liquid Layers – Try with your neighbor

• Which liquid has the highest density?

• Which liquid has the lowest density?

• Which liquid has the middle density?

Liquid Layers – Try on your own!

• Imagine that the liquids on the right have the following densities:– 15g/cm3 10g/cm3

– 3g/cm3 9g/cm3

– 7g/cm3 12g/cm3

• Match the colors to the correct densities.

3g/cm3

7g/cm3

9g/cm3

10g/cm3

12g/cm3

15g/cm3

Review• What is mass?

• When finding mass, what tool do you use?

• When finding mass, what unit do you use?

• What is volume?

• When finding the volume of a regularly shaped solid, what tool do you use?

• What final metric unit do you use?

• What is the formula?

Review

• What is density?

• What is the formula for density?

• What metric unit do we frequently use in class for density?

• What happens if you pour together liquids that have different densities?

• Will the liquid on the top have the highest or lowest density?

• Will the liquid on the bottom have the highest or lowest density?

Super Scientist Question of the Day

• Jake has a book, a ruler, and a balance.

• How can Jake find the density of the book with the tools he has?