Density

Mrs. Reese

What is density?

1. Density is the measurement of the compactness of an object.

2. Density is a physical property that is determined by the ratio of a substance’s mass to its volume.

3. Mass is how much matter is inside of an object.

4. Volume is how much space something takes up.

Density

All substances (solids, liquids, or gases) have unique densities.

Density is a GREAT way to indentify unknown substances!

Which one is more dense?

Demonstration: People in a square

How about this: Which square is more dense?

Which one is more dense?

Now which one is more dense?

What is density?

Density = mass OR mass ÷ volume.

volume

Units for density: g OR g .

cm3 ml

ALWAYS REMEMBER

UNITS!

How can density be affected?

There are some factors such as change in temperature or state of matter that can affect the density of matter.

As a GENERAL RULE, solids tend to be more dense than liquids or gases because their atoms are more compacted within equal volume.

EX: Liquid gold has a density of 17.3 g/ml while solid gold has a density of 19.3 g/cm3.

There is ALWAYS an exception!

There is ALWAYS an exception…

When you freeze water, the density of the ice is LESS than the density of water (even though they are both the same substance). When you freeze ice, it crystallizes and leaves more gaps which increases the volume (by about 9%) and therefore the density goes down.

THUS, ICE CAN FLOAT IN WATER!

Water vs. Ice

How can density be affected?

Example: Hot air balloon

When you heat a gas, it expands (increasing its volume) and therefore decreasing its density. Warmer air rises because its density is less than the surrounding air.

CAREFUL! What Won’t Affect Density?

Cutting an object into pieces WILL NOT change its density. You have not changed the particle compaction in any way!

Example: If the density of a piece of American red oak wood is .74 g/cm3. If you cut the piece of would in half, the density would NOT decrease by two, IT WOULD STAY THE SAME!

What can float on water?

Density of water is 1.0 g/mlIf the density is greater than 1.0 g/ml, then

the object will sink in water.If the density is less than 1.0 g/ml, then

the object will float in water.

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?

Liquid Layers – Try with your neighbor

Which liquid has the highest density?

Which liquid has the lowest density?

On your own…

Your friends at your lunch table all have different stuff in their lunch. Liquid A has a density of 1.07 g/ml, Liquid B has a density of 0.98 g/ml, Solid C has a density of 1.12 g/cm3, and Mush D has a density of 1.03 g/cm3. You decide to make a gross combination of the four in your water bottle. Which order will they appear in, from bottom to top?

a) Solid C, Mush D, Liquid A, and Liquid B on top?b) Solid C, Mush D, Liquid B, and Liquid A on top?c) Solid C, Liquid A, Mush D, and Liquid B on top?c) Liquid A, Liquid B, Solid C, and Mush D on top?

5 special steps-that’s all you need!

Let’s try a density problem together

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

Frank also has an eraser in the shape of a cube. It has a mass of 3g, and each side of the eraser is 1.0 cm long. What is its density?

Work on these problems with your neighbor.Jack has a rock. The rock has a mass of

6g and the volume of the water level went up from 50 ml to 53 ml when placed inside. What is the density of the rock?

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?

Al’Licia has a watch. It has a mass of 4g and a volume of 2cm3. What is the density of the watch?

Now, try these on your own. ON CLEAN SHEET OF PAPER….A cube made of very old hard wood, has a mass

of 45g and measures 6cm a side, will it sink or float?

Mia has a wallet. It has a mass of 15g and a volume of 5cm3. What is the density of the wallet?

A block has a mass of 20g and measures 2cmX4cmX2cm, will it sink or float?

Try these on your own…

From their density values, decide whether each of the following substances will sink or float when placed in sea water, which has a density of 1.025 g/mL.

Gasoline 0.66 g/mL Asphalt l.2 g/mL

Mercury 13.6 g/mL Cork 0.26 g/mL