What's a line of best fit?

Student in Algebra I are often asked to solve equations and manipulate variable without considering with the x's and y's represent. Last week, our eighth grade had the opportunity to take their understanding of variables, coordinate geometry, and see how real-life situations can be modeled.

Each group of students used rulers to measure the length, width, and height of various wooden blocks. Once the dimensions were know, the teams calculated the volume for each block Following this, the remaining variable to be calculated was the weight of each wooden block using a balance-scales.

With these data sets, each group plotted the mass (weight) and volume on an x-y graph and this is where the fun stats.  Groups noticed that the data seemed to behave in a strangely predictable way.  The data points were spread out along a line originating at the origin.