## Tuesday, November 2, 2010

### Density

What is Density?
-         Density is a physical property of matter
-         Density defined in a qualitative manner as the measure of the relative "heaviness" of objects with a constant volume.
-    Density may also refer to how closely "packed" or "crowded" the material appears to be – think of a  styrofoam vs. ceramic cup.

The ceramic cup is much denser than the styrofoam cup.

Density = Mass / Volume

We can use this density triangle to easily isolate a desired variable.

D = M / V
M = DV
V = M / D

Units
For a solid we usually (but not all the time) use  g/cm3
For a liquid we usually use (but not all the time) use g/ml

Water and Density

1 cm3 of water = 1 mL
Density of water = 1.0 g/mL
Or = 1000 g/L

The density of many substances is compared to the density of water. Does an object float on water or sink in the water

D object > D Liquid  = sink
Example. A rock sinks into water
D object < D Liquid  = float
Example. A piece of wood will float on water.