Matter is a substance that has volume and mass. Volume means that it takes up space. Mass is the amount of matter something is made of. Mass can be measured in kilograms, grams or milligrams. Matter comes in three basic states: solid, liquid and gas. A fourth state, plasma, only occurs under very special circumstances.
All substances are made of matter, and matter itself is made up of particles, including single atoms and/or molecules. Because different atoms have varying numbers of protons and neutrons in their nucleus, the matter of different substances contains different masses.
Density is the amount of matter a substance has in a given amount of space. Density is a useful measure because it isn't affected by pressure or temperature. If two objects have equal volume, but one has more mass, the one with more mass is denser. If a something has less density than a liquid, it will float on top of it; if it's denser, it will sink.
Oil is less dense than water. What happens when you mix the two liquids together?
A
Oil sinks to the bottom of the container.
B
The two become one smooth mixture.
C
The oil floats on top of the water.
D
The water turns to gas inside the oil.