Raymond W. Brooks
The metric system of measurement is used in all branches of science and more experiences are needed to become more comfortable and competent with this system of measurement.
A good introductory filmstrip is entitled “A HISTORY OF MEASUREMENT” by Learning Resource Company. This filmstrip traces the early standards of measurement and the problems with these standards to the presently accepted standards of the metric system.
We will begin with the measurements of mass (grams or kilograms), volume (liters), length (meters), and time (seconds). After mastering these basic units we will find the density of several objects using the techniques we have used to find and volume.
Mass is the preferred term to use over weight when describing properties of matter as matter can become weightless but it does not become massless.
The balance is the instrument we will use to measure mass in the middle school. The introductory assignment with the measurement of mass should involve a teacher demonstration/explanation on the use of the balance and the introducing of the following terms: gram—beam—adjustment knob—riders—zero point.
After the introductory lesson, a good homework/follow-up activity would be Lab Skill 3 from “Basic Skills in the Laboratory” by Charles E. Towne and published by Cebco Standard Publishing Company, copyright 1977. This exercise gives the student an opportunity to practice reading the position of the riders on the beams before they begin the practical application exercise.
The practical application should begin by giving students objects of known masses to help their confidence with the use of the balance. After this has been completed the massing of some common objects in metric units is also helpful.
A good way to end this section is to give the students 10 marbles and have them find the mass of 1-3-5-7-9 marbles and plot the results on a graph with the number of marbles vs the mass of marbles. They should then use the graph to interpolate the mass of 2-4-6-8-10 marbles. If so desired, the percent of error can be found by comparing the results from the graph against the actual mass of 2-4-6-8-10 marbles and using the following formula:
real mass — estimated mass % error = ————————————— x 100% real mass
Volume will be found by using the graduated cylinder and overflow can. Even though the mathematical procedure is more accurate when used in our laboratory setting, at this point it is more important to introduce new techniques and procedures than to obtain exact answers.
A good homework assignment is Lab Skill 2 in the same “Basic Skills in the Laboratory” by Charles E. Towne. This exercise explains the meniscus and gives examples for reading a meniscus in the graduated cylinder.
Continued use of the marbles for the practical application is advisable for this exercise. When using the graduated cylinder to find the volume of the marbles directly, place a rubber stopper in the bottom of the cylinder to absorb the shock and prevent breakage.
As with finding the mass of marbles repeat the same procedures of finding the volume of 1-3-5-7-9 marbles using the graduated cylinder and graphing the results of volume of marbles vs number of marbles.
Using the graph interpolate the mass of 2-4-6-8-10 marbles. If so desired, again you can find the percent of error by using the same formula as was used for finding percent error with mass.
If you would like them to try finding volume of the cylinder using the mathematical method, a fun exercise is to use a coffee can and the graduated cylinder. Using the formula V = 3.14 x R x R x H they can find the volume and then check their results by using the graduated cylinder and water. If possible, it is best to use a vernier caliper for your measurements.
The measurement of length in meters and centimeters seems to be the most common units used by middle school science students and so the emphasis will be with these units when measuring objects.
After the demonstration/explanation of the meter stick and metric ruler is completed a good follow up exercise is Lab Skill 1 in Basic Skills in the Laboratory” by Charles E. Towne.
Students should then be allowed to measure various common objects to become more familiar with their dimensions in metric units. Estimating sizes and distances is also a good activity and finding their percent error always adds to the fun.
Other activities could be to find their pace (amount of steps to cover 10 meters) and find distances to various places using their pace. If possible, the actual distance could be found and the percent error calculated. Having the students measure themselves on the wall in metric units and comparing their differences in height and also finding the average height for boys, girls, and the class can help them to relate to metric units.
Another activity could be the use of the triangulation method to find the distance to an unknown object. Again the actual distance could be found and the percent of error calculated.
If you have access to vernier calipers, students enjoy working with these as their measurements are more accurate and they are learning to use a new instrument. A good source of information for the use of the caliper is “Selected Experiments for Elements of Physics” by Buchanan and Murphy. This text can be probably be found at the SCSU bookstore as this was written for their physics course.
Although we use the same units of time in both the english and metric system, we should spend time understanding some time intervals such as the second, minute, and then larger units for describing various events in earth history.
A good textbook for this is “Interaction of Earth and Time” published by Rand McNally & Co. 1972.
This text begins with the students estimating various time intervals without any method of counting and then gives them a method of counting to become more accurate with their estimation of time.
The unit also has an activity that will help them to better understand the vastness of time and time intervals between various events in earth history by constructing a time line on adding machine tape. This allows the student to visually see the distances between the lines which represent events that have happened since the origin of the earth.
The finding of density is a good way to tie up this section on the metric system as we have to find the mass and the volume in order to find an object’s density.
A suggested way to start this topic is to have the student find the density of one rubber stopper and then the density of two rubber stoppers. We can again use our graphs on the volume and mass of marbles to figure out the density of glass. This exercise impresses the fact that the amount of the same type of matter does not affect the density of an object and can be used to distinguish similar looking objects from one another.
The evaluation of this topic can be the finding of density of some objects such as brass, copper, lead, and aluminum. After determining their densities, construct a bar graph to visualize their differences.
We are now ready to study the atmosphere to prepare for our study of aerodynamics.
