1. Density notes and practice
Monday, August 31, 2015
Objective: Students will determine the density of objects using the equation, displacement and the density table.
Warm-Up
What would take up more space: a kilogram of feathers or a kilogram of steel? Which is more dense? Why?
Agenda
Density notes and practice
ROCKS - pass around

2. Density = amount of matter per unit volume
Density is the ratio of mass to volume
If the volume stays the same and the mass increases the density will increase
If the mass stays the same and the volume increases The density will decrease

3. DENSITY D = m/v (g/cm3) Mass usually expressed in grams
Volume usually expressed in cm3 or liters, etc.

4. Density is the measure of the “compactness” of a material
How close the atoms or molecules are to each other
More than “heaviness” - density includes how much space an object takes up!!
All substances have density including liquids, solids, and gases. It is a physical property of the substance.
Bread slice and compacted bread in large flask of water

5. “Compactness”
Hot air balloon - Describe how a hot air balloon works. Defend your argument.

6. How to solve for density using the density equation:
Write out the formula for density: D= m/v
Identify your known variables.
Identify the variable you are solving for.
Plug in the known variables into the equation.
Solve for the missing variable.
Write your answer and don’t forget to include units!

7. Example:
A 10.0 cm3 sample of copper has a mass of 89.6 g. What is the density of Copper?

8. Example:
What is the weight of the ethanol that exactly fills a mL container? The density of ethanol is g/mL.

9. Example:
What volume of silver metal will weigh exactly g. The density of silver is 10.5 g/cm3.

10. Brain Break: Statuesque Dominoes

11. DETERMINING DENSITY Use a graduated cylinder
Regular Shapes – mass, then determine the volume by formula
EX: cubes, cylinders, spheres, cones, etc.
Irregular shapes – mass, then measure displacement of a liquid (usually water) by that irregularly shaped object
Use a graduated cylinder
Add water to a predetermined level - record.
Gently drop in the irregularly shaped object.
Read the graduated cylinder – record.
Subtract the first water level from the second – this is the volume

12. Density Table
All known substances already have a calculated density. We put these numbers into a density table.
We assign water a density of 1.00 g/cm3.
We can compare the density of other objects to determine if they will float or sink in water.
If the density is greater than 1.00 g/cm3, the object will sink in water.
If the density is less than 1.00 g/cm3, the object will float in water.

13. Density Table SINK or FLOAT In Water (D = 1.0 g/mL) Float Float Float
(alcohol)
Float
(fuel)

14. What would happen???? Mercury density = 13600kg/m3
Lead density = 11340kg/m3
Sinking vial - make it float

15. Lead floats on liquid mercury!

16. Solids
Ice vs. water…..

17. SOLIDS
Ice is less dense than water (which is why lakes and ponds have a thin layer of ice covering in winter, with water underneath)
Various rocks, woods, metals have a characteristic density specific to that substance
Beans/ping pong ball; Big jug of water in a pool
Wouldn’t you like to have a bunch of THIS dense material?