Units, Measurement, & Estimation
Standard reference units are important in scientific — and everyday! — communication. For example, an inch is the length of three barleycorns in a row. Why barleycorns? Because barleycorns were a handy item that don’t change in size, so by using barleycorns instead of, say, the length of a person’s foot, people could be sure that everyone mean the same length when they said something was 12 inches long.
Today there are seven official base units, and all but one of them use physical laws to define them. A second is defined as the distance light travels in a vacuum in 1/299,792,458 seconds, and a second is defined in terms of the atomic activity of the Cesium-33 atom. The only standard that is still defined by a physical artifact is the kilogram. Ask your students why this is a problem today!
Standard units can also help us estimate measurements in our daily life. If we have something to compare to, also called calibrating, we are better equipped to accurately estimate the size, weight, or volume of something. The students practiced this by first estimating some measurements without any tools, and then by using either rules of thumb or standard references to calibrate their guesses. The calibrated guesses were a lot closer to the actual measurements!
We also learned that anything can be used a standard unit, and that is why we know that the Harvard Bridge is 364.4 Smoots long, plus one ear.