The focus of this lesson is twofold: to acquaint students with making measurements using metric units and to make both quantitative and qualitative observations to better understand the importance of both.
I actually linked this lesson to a 5th grade math standard. I know that may sound ridiculous for a high school class, but in my experience, it at least needs a review because the majority of my students aren't readily familiar with the prefixes of the metric units, the numerical values they represent, or the simple calculations necessary to convert between units. This may not be the case in certain schools, but it is a reality many teachers face in an inner-city urban school.
The high school math standard of this lesson deals with selecting appropriate units for precise measurements and several of the stations of the Exploration activity have requirements for students to make separate measurements of the same object, with follow-up questions requiring them to reflect on the advantages and disadvantages of different units of measurement.
The Exploration activity requires a bit of set up prior to beginning the lesson. See page three of the Collecting quantitative and qualitative data worksheet for a description of each station.
I try and have the following measurement tools at as many stations as possible: rulers, meter sticks, precision digital scales, and standard scales.
To begin this lesson, I ask students if they know how tall they are. Most high school students are acutely aware of their height, so this is a relatively easy question for them to answer. The switch is to ask them to state that in centimeters. In all but most cases, students have no idea. If you have a measuring tape attached to the wall, you may ask a student to come up, tell their height in feet and inches, and then measure them against the metric tape. You may then ask another student to do the same. After you get those values (preferably from students of noticeably different heights), you can ask students to predict their own height in centimeters.
This can act as a segue to discussing the prefixes used in the metric system. If your students are Spanish speakers or simply study Spanish, you might ask what cien means in Spanish. If not, you might ask it a different way and ask how many years there are in a century. The point is for students to get to the point where they see centi- means a hundredth and that there are 100 cm in 1 m (You can also do this with millimeters using the Spanish word mil and/or a millennium).
After the basic practice with etymology in the warm up, I distribute the Metric Mania worksheet from sciencespot.net (I actually only print pages 2 and 3 of the pdf as page 1 is missing some of the helpful info on page 2, and page 4 is an answer key).
This sheet introduces the “ladder method” of conversions between metric units and it is helpful to practice a few of these together with the whole class. The prefixes provided on the sheet only go as large as 1,000/1 (k or kilo-) and 1/1,000 (m or milli-), but you may add 1,000,000,000/1 (G or Giga-), 1,000,000/1 (M or Mega-) on the large side and 1/1,000,000 (µ or micro-) and 1/1,000,000,000 (n or nano-) on the small side if you wish, just make sure students understand that they must move 3 decimal places to the left or right when converting to these units from kilo- or milli- respectively (and 3 more to go to the next larger or smaller unit). Go nuts with Tera- and pico- if you’re really into it. (Please note that many, but not all, of these prefixes can be found on the list of scientific prefixes and suffixes that students received as part of the earlier lesson on scientific terminology. Nonetheless, this is a good time to have students build on a previous lesson and practice using that additional resource to develop the habit of approaching new vocabulary strategically.)
Once it’s been introduced, I allow students to work on the worksheet with their partners (though each student has their own sheet) while I go around to check that they are able to complete the conversions properly, addressing any misconceptions or problems as they arise. This is a deceptively simple assignment and students often develop bad habits that are hard to break, so it is important to try and check in with all students. I usually have an answer key with me when I check the work just to make sure I’m not making any casual errors.
After students have had about 20 minutes to work on the worksheet and I have had time to check with all groups, I distribute the next activity “Collecting quantitative and qualitative data” (I distribute the first two pages as a double-sided worksheet to pairs of students, the third page is a teacher's guide describing the set-up of each station. I find it easiest to print it once and then make several photocopies of the first two pages as needed).
In this activity, there are several stations set up around the room and students are required to collect data from at least 4 stations. At each station, students use measurement tools to collect quantitative data and their senses to collect qualitative data.
(depending on the resources available, I try and have the following at as many stations as possible: rulers, meter sticks, precision digital scales)
Students are required to visit at least four stations, and although they can choose three of the stations they want to visit, one station that all students are required to stop by is the two liquids station (for this reason, I have it set up in two or three places around the room). At this station, students look at the amount of a liquid and make a quantitative measurement (easy enough to do in a lined beaker). Since the two liquids are water and vinegar (I don’t mention this to them beforehand), qualitative measurements are also important. One of the liquids is poured into a beaker lined with metric units while the other is in a measuring cup lined with cups or fluid ounces. Students are asked to convert the liquid amount to a larger unit (mL to L) and (oz or cup to gallons).*
Hopefully this process drives home the point of why metric units are preferable to other units in science. Students are required to answer this question on their own, but it is something we go over in the wrap up at the end of the lesson.
*Although I prefer to have students have to do their own research about how to do these conversions (to further underscore the elegant simplicity of the metric system), it may be helpful in the interest of time to let students know that 1 cup = 8 fluid ounces, and 1 gallon = 16 cups. Trust me, it's still confusing.
After everyone has finished making their measurements and collecting their data, we have a short discussion about the two main questions in the activity:
1. Why do scientists prefer to use metric units?
2. Why is it important for scientists to collect both qualitative and quantitative data?
Answers will of course vary, but for question 1, I try to get students to undertand that metric units allow for quick conversions between large and small units AND they are the international standard so it is easier for scientists to share information with colleagues around the world (this second point isn’t explicitly part of the lesson, but it usually comes up in the earlier discussion)
For question 2, I hope that students understand that there are important details that can not always be expressed in quantitative or qualitative data alone. A more holistic understanding of a phenomenon requires both kinds of data. (e.g., the quantitative data about how many eyes your partner has is fairly useless… even when looking at the whole class. However, the color of your partner’s eyes may be of more value in describing them or the whole class [not to mention that quantitative data can be derived from collecting this qualitative data from multiple students]).