A function is a relation between one property and another property of an object or system. In other words, if you can say that y is one property and x is another property and y=kx, where k is a constant of proportionality, then you have a function! k can come from experimentation or from a table of constants that have been derived through the years. k basically "fixes" the x so that it agrees with the y.

Numbers are fun little things to play around with. They're useful too, incidentally. They help scientists and regular people (pun intended) assign values to objects or attributes of those objects. For example, you can count a number of objects such as 5 apples, or one can lift a 5 pound weight. If one cannot lift a 5 pound weight, something is usually seriously wrong.

Now it is the attributes of these objects that get really interesting. Humans have a tendency to place values on everything they see around them, in an attempt to "understand" these things. For example, 5 pound weights feel heavier than 10 pound weights. Now why is that? Well, after thinking about the problem for a long time, the concept of "Forces" was slowly coalesced into existence. Sir Isaac Newton is usually credited with this remarkable jump in understanding, and indeed his laws of nature were revolutionary at the time.

Now, if you haven't heard of functions before, you're probably wondering what all this talk has to do with old f(x)=y. Well, here's the gist. To understand something abstract in physics, one usually has to link it to things that one does understand. We usually say that the unknown quantity (let's call it y) is proportional to the known quantities by a constant "k". Another way of saying this is that y is a function of the known quantities.

Now one may ask, how can someone find which properties of the object are proportional to the property we are deriving ? Well, the only way is through common sense, experience, and something called dimensional analysis. Dimensional analysis(sounds big and advanced doesn't it?) is simply making sure that both sides use the same units of measurement, or dimensions. If you have grams per liter on one side, you want to make sure that the final product on the other side is also grams per liter, or it won't make much sense, will it?

Now let's get out of theory, and look at a real problem. If you have a table of data such as the one below: