Density
Because all objects are made out of molecules, it is possible
to determine how tightly packed those molecules are. This is
known as density. The more tightly packed the molecules of
an object, liquid or gas are, the more dense the object is.
Imagine you have two balls that are the same size and
shape, but one is filled with air and the other with sand. The volume (or amount of space
the ball takes up) is the same for each ball, but the ball that is filled with sand will have a
much greater mass and will also have a greater density. Imagine that you have two boxes –
one large (about the size of a desk) and one small, like a shoebox. Which box would be
easier to lift? If the desk size box is empty, you would think of it as being “light” or easy
to lift. But, if the shoebox were filled with rocks, you would think of it as being “heavy”
for its size. The density of an object effects the way we perceive its weight.
The words “light” and “heavy” are useful in everyday language, but scientists need a more
reliable description. We can calculate the density of an object by using a formula. An
object’s density equals its total mass divided by its volume.
Density =
Mass/Volume
The particles placement in matter will affect its density. If the particles are very close
together, the object will be more dense and will sink in water. If the particles are more
spread apart, the object will be less dense and will likely float in water. The particles in
gas will spread out into the container in which the gas is placed. If the container is large,
the density of the gas (or how close the particles are) will be less than if the container is
small. A small container size will force the particles of gas to be closer together and the
density of the gas will increase.