Basic Skills and Principles: Measurement

Introduction
Measurement

In general, you are quite familiar with measurements, as almost any occupation requires measurements of some kind. Carpenters measure boards for cutting, nurses measure blood pressure in patients, tailors measure fabric for garments, and advertising executives measure the public's acceptance of their sales pitches. You will therefore undoubtedly be utilizing measurement in your chosen career, regardless of the field you enter.

Measurement plays a particularly large role in science. In their studies, scientists gather data, and to do this they use measurements. Scientists measure the concentration of gases in the atmosphere, the growth of organisms under varying conditions, the rate of biochemical reactions, the distance of stars from the earth, and an innumerable number of other things. As measurements form the basis of scientific inquiry, they are deserving of in-depth analysis in lab.

In a scientific experiment, the investigator examines the effects of variations in the independent variable on the dependent variable through measurements. For example, let's assume a biologist is studying the effect of temperature on plant growth. She sets up several different temperature conditions, and grows groups of plants from seedlings in each condition. When the experiment ends, she must compare plant growth in the plants from different temperatures. But how should she do this? Should she just look at the plants and decide which grew the best? Should she pick up the plants and "feel" which ones have the greatest mass? Of course not. She would use some sort of quantitative measurement, such as measuring the height of each plant's stem in centimeters or determining the total plant biomass in grams. Whichever measurement she chooses, she would need to utilize an instrument to make it, and this takes us to our next section...

Instruments Take a minute and look around you at the variety of objects surrounding you. There's probably a few pens or pencils, a notebook or two, assorted computer equipment, and other things. While you may be able to easily distinguish the differences between some objects (e.g., your notebook is longer than your pen), other differences are more difficult to discern. You may not be able to easily determine, for example, whether your computer keyboard or your course textbook has greater mass. Even when we can distinguish differences, it is not always easy to determine the extent of those differences. You may have noted that your computer monitor is heavier than your notebook, but is it twice as heavy or three times as heavy? Using only our senses, we cannot be certain about the answer, so we must take measurements.

To take measurements we need instruments. Instruments include simple things like rulers and graduated cylinders, and complicated electronics like pH sensors and mass spectrometers. All of these instruments provide us what our senses cannot - a quantified measure of the properties of an object. In today's lab you will use get an introduction to measurement by using various instruments to measure the linear dimensions, volume, and mass of objects. As all scientific measurements utilize the metric system, we must first say a few things about it before proceeding on to this week's exercise.

The Metric System
If you are measuring something, you need "units" to describe the object. In formal terms, a scale of measurement is the assignment of numbers or symbols to measure an attribute. In the past, natural units of measurement, such as a "foot", were commonly used. Unfortunately, these units were somewhat arbitrary. In Roman times, for example, a "foot" in England was 29.6 centimeters. When the Saxons took over, the size of a "foot" grew to 33.5 cm. Five centuries later, it was reduced to 30.5 cm. Finally, in 1959, the "International Foot" was defined as 30.48 cm. Even today, a "foot" in England is different from a "fod" in Denmark (31.41 cm), a "fod" in Sweden (29.69 cm), and a "fuss" in Germany (31.61 cm) (Rowlett, 1998). With the increase in international trade during the 18th century, merchants needed to standardize units of measurement. This resulted in the development and nearly universal adoption of the metric system around the world. Of course, the United States is a notable exception to this worldwide trend, as we continue to use the English system of measurement. We buy our gas in gallons, measure our weight in pounds, and gauge driving distances in miles. The metric system has crept into our society somewhat (e.g., the two-liter soda bottle), but universal acceptance of this system of measurement anytime soon is unlikely.

In science, use of the metric system is unquestioned. Because of its international familiarity and ease of use, scientific studies utilize metric measurements. All of the measurements you make in this course must therefore be in metric units, and this is something you should keep in mind throughout the semester. Now as we've all dealt with the metric system during high school, a review of the system will not be provided here. If you need some refreshing on the material (it may have been a while for some of you), please visit the web sites below for additional information.

So how important is it to list the units you're using when measuring? Listen to the segment below from National Public Radio to learn about an instance where confusion over measurement units had some very unfortunate results...