Today we practiced estimating and measuring length, volume, and weight. We considered the length of a piece of rope, the volume of a bowl, and the weight of a bag of glass beads. We first estimated blindly, using our own knowledge of centimeters, milliliters, and grams. Then we estimated again, but this time using a reference object for comparison: a string of known length, an 8-ounce juice cup, and a reference weight.
Finally, we used a ruler, a graduated beaker, and a spring scale to measure the objects. For each round we graphed the data obtained by the whole class to see which set of data was the most precise and accurate. To no one’s surprise, the measured data was the most accurate, but the calibrated estimates were pretty accurate as well, once we averaged the whole class’s data. It was interesting to see that having lots of measurements actually increases the overall accuracy of the average measurement! We also talked about how the precision – or repeatability – of a measurement depends mainly on the tool used to measure something, but of course the scientist doing the measuring has to be careful, or he or she may end up with inaccurate and imprecise data!