1. Density
Mrs. Reese

2. 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.

3. Density
All substances (solids, liquids, or gases) have unique densities.
Density is a GREAT way to indentify unknown substances!

4. Which one is more dense? Demonstration: People in a square
How about this: Which square is more dense?
right

5. Which one is more dense?
Now which one is more dense?
left

6. What is density? Density = mass OR mass ÷ volume. volume
Units for density: g OR g
cm ml
SI units
ALWAYS REMEMBER UNITS!

7. What if I need mass or volume?
Mass = D x V mass =density x volume
V = mass volume = mass ÷ density.
density

8. 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.

9. There is ALWAYS an exception!

10. 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!

11. Water vs. Ice

12. 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.

13. 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!

14. What can float on water? Density of water is 1.0 g/ml
If 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.

15. 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.

16. 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?
Top->Bottom: 3g/cm3,5g/cm3,6g/cm3,10g/cm3