DENSITY is a measure of the ratio of a substance's mass to its volume.
Density is putting a value on how close all particles are squished together in a substance.
The formula to find a substance's density is d=m/v
OR
DENSITY= MASS divided by VOLUME
d= density m=mass v=volume
The theory about density is that when a substance has a greater density than one near it (on top/bottom/within), the greater density will sink, while the lesser density will rise above it.
Think of helium-filled balloons, the balloon will float because the helium inside of it has a lower density than the air we breathe! This is why when you let go of the balloon's string, the balloon seems to travel upwards forever- the balloon is trying to get above the air's density because it has a lesser density!
Look at these layered liquids. Why don't they mix together?
If you said they don't mix together because of their densities, you are correct!
The clear substance that sits on the top of the other liquids has the least density, while the yellow-ish substance at the bottom of the bottle has the greatest density.
Source: Flickr, http://www.flickr.com/photos/27238916@N04/3920970822, July 30 2010
ALWAYS REMEMBER d=m/v!