This is a very powerful question. The answer to it tells one a lot about us as a species that
interacts with the world. The simple answer is that the density of water is one. That's it!
Well, OK, actually I've given you the specific gravity of water. The actual density of water is
one gram per milliliter. You can see that the specific heat of a substance is the same as its
density without the units.
So, now that you know this, what does it tell you about us as a species? Well, we are the ones who
said that the density of water is one gram per milliliter. How did we come to this decision? We
had to first decide what a meter is so that we could know what a decimeter is so we could make a
liter (a cubic decimeter) and then we could make a millimeter which we could fill with water and
call it a gram! So, if you ever find yourself in a desert island you too could make a milliliter by
getting a gram of water!
Of course it cannot stay this simple! You have a gram of water in one milliliter only if it is at 4
degrees centigrade. As you know materials expand and contract with temperature. Water's density
is one gram per milliliter only at 4 degrees centigrade and at one atmosphere of pressure since
pressure also affects the density of liquids.
So, in the end, if you ask what is the density of anything, you have to define its temperature and
its location so that we can know the atmospheric pressure.
Answered by: Tom Young, B.A. Science teacher, Whitehouse High School
Although the density of water varies somewhat with
temperature and pressure, and is higher for salt
water than fresh water, you can use about 62 lb
per cubic foot for its weight density in English
Water was used as the basis for establishing the
metric unit of mass, however, so it is easier to
remember that a cubic centimeter of it has a mass
of 1 gm. Knowing that there are 1000 cubic centi-
meters in a liter, you can also use 1 kilogram
(1000 grams) per liter for water's mass density.
Answered by: Mr. Paul Walorski, B.A. Part-time Instructor
'Physicists like to think that all you have to do is say, these are the conditions, now what happens next?'