Designing PMRI Math Class: Introducing Formal Unit of Weight



Irkham Ulil Albab, I ketut Kertayasa and Wahid Yunianto

International Master Program on Mathematics Education (IMPoME) 2012

Sriwijaya University

  1. A.    Introduction

A lot of Problems are related weight can be found in everyday life. For example when the mother is baking a cake. The composition of flour, sugar and other ingredients are usually measured by weight. Traders also consider snacks that bear heavy loads and position on a pole be balanced so easily borne.

The introduction of the concept of weight measurement is very useful in those problems. How students can compare the weight of two objects, comparing the weight object with one object as a benchmark, and measure the weight of objects with a standard unit.

Therefore, the learning of mathematics concerned with weight measurements should be raised significantly one of which is with PMRI. The real world is used as a starting point for the development of mathematical ideas and concepts (Hadi, 2005). One in the real world it can be a device for the student newspaper.

  1. B.     Design Research
    1. 1.      Preliminary Design

Observations conducted on students of class 2 SD PUSRI Palembang on Wednesday, November 21, 2012. Standard of Competence to be achieved is the measurement of time, weight and length of the elaboration of the Basic Competence weight measurements. Indicators of objectives are learning students can compare the weight of objects, students can measure the weight of objects with a gauge and students can use a heavy gauge appropriate purpose. Of these indicators, learning objectives is structured as follows: students can compare the weight of objects, students can measure the weight object with non-standard units, students can measure the weight of objects with standard unit, and students can use a heavy gauge to the purpose.

The purpose of learning is planned learning PMRI. Stages step towards formal mathematical activities performed by formal mathematical steps as follows:

  1. Activity comparing the weight of two objects is directly
  2. Activity compare two objects with non-standard unit of measurement
  3. Activity measure objects with formal unit
  4. Activities using heavy gauge formal

In the first activity students will discover which objects are heavier. Such items include stationery they have. For the initial activity, students will compare objects without tools. Because students will surely find it difficult to weigh the two objects are slightly different, the teacher provides assistance formal scales. They can compare the weight of two objects correctly.

In the second activity, students will be set to compare the weight of two objects with other objects as a measure, such as a pencil, because a pencil is a thing that most of the student.

The third activity, students will begin to recognize formal unit: grams and kilograms with the help of formal scales. Teachers will ask students to guess which products are heavier (two different soaps). Students are expected to have a lot of strategies and understand how to guess grams to kilograms relationship.

In the last activity, students will begin to measure the weight of objects formally. They will measure the weight of each and write it on the board. With the help of two types of scales that scale household and body weight scales, students are expected usefulness of each tool.

Here is picture of the achievement of formal mathematical concept of activity traced through the above activities.



  1. 1.      Teaching Experiment

The first activities:

Open class by asking students unload their bag on the table. Students begin to mention the stationery they have. Through the activity compared with the hand, students can know the difference in weight between the two distinctly different writing utensils weighs like a pencil with books. When students compare a pencil with an eraser, students begin to have difficulty determining which objects are heavier(figure 2). Therefore, teachers provide simple scales (balance) as aid (figure 3).


Figure 2. scaling using hand                                      Figure 3 Using simple scale


Some students are able to use all those tools properly but some cannot communicate how the position of the scales if one object is heavier. After several questions were directed to the question, students could finally explain the tilt position objects lighter and heavier.

Activity 2

The teacher asks students to compare objects that they have with a pencil. Through the use of pencil as a unit of weight measurement is not standard, students can determine which objects are heavier. For example, a single ruler weight equal to 2 pencils and an eraser equivalent weight of 3 pencils. Students can understand the intent of using the pencil as a measuring tool is not standard. Problems that experienced by students are that they cannot collect a lot of pencils to measure the weight of a thick book. Another problem is that they have pencils uneven in size. Problems also exist in simple scales to accommodate books and pencils in bulk.

Activity 3

Finally in the next activity, the teacher brought two packs of soap. With a similar question, namely soaps which are heavier, some students compare directly on simple scales. There is also a measure used by comparing them to weight of pencil. The difficulties encountered are not enough pencils to measure weight. Teacher shows the writing on the packaging of the soap weighing 100 grams and 75 grams. Students know from simple scales that soap that is labeled 100 grams heavier than 75 grams of soap. Teacher points a note that in its as a formal unit of weight measurement. When the teacher is introducing formal scales: household weights and scales(figure 4).








Figure 4. Introducing formal scale


Students took turns fiddling with scales for weighing household equipment they have. Their peculiarities encountered when the total weight of the book should reach 1000, but the number shown on the scale is 1 kg. Teachers insisted it was another tough unit. Students conclude 1000 gram equal to 1 kg. In this activity students know the scale also has a size limitation. Small scale objects weighing small and large scales for objects that have a heavy weight are like students.

Activity 4

Students measure weight of objects using formal scale. They can read the number of weight from the scale and read it on the board.

  1. 2.      Retrospective Analysis

Student activity

During the learning activity, students tend to work independently. Students actually planned to be set to learn in groups but it seems easier to classical interaction controlled by the teacher.

At the stage of comparing the weight of two objects, the students were not able to easily communicate what scales position if one object is heavier than the other. Communication skills should be trained so that others can know the intent of the student activity. Students actually understand how to use the scales from their answers were correct in determining which objects are heavier.

By the time students make the size of a pencil weight as non-standard unit of weight, a lot of the same size pencils difficult to meet. Moreover, for objects that weigh are very much different from the pencil.

The strategy of the student in heavy activity comparing two different soaps is that students tend to compare it directly to the scales simpler than using a pencil as a comparison. With the formal scales, students are able to correctly determine which is greater bend and find that 100gram heavier than 75 grams as they discovered on a simple scale. Students also do not have trouble with the scales.


Learning Tools

Student activity sheets (LAS) was unable to steer students clear. Some point in the activity sheet even confusing students. As a result, students leave some questions in LAS.

  1. A.    Conclusion

After learning activities are completed, acquired the following benefits:

  1. Students can compare the weight of two objects with simple scale.
  2. Students can understand the purpose of considering the weight of the object compared to other objects As with non-standard units.
  3. Difficulties experienced when measuring weight of objects with non-standard units to make students understand there must be a reliable unit.
  4. Students can measure the weight of objects with formal scales.
  5. Students know the usage and limitations of each scale.


Hadi, Sutarto.2005. Pendidikaan Realistic Mathematics. Banjarmasin. Tulip


Tentang Irkham Ulil Albab

Adalah kesempatan terbesar bisa bertemu dengan para pendidik Matematika yang hebat. Keinginan terbesar saya bisa menjadi the Future Lecturer, Future Researcher, Future Designer and Future Leader on Mathematics Education
Galeri | Pos ini dipublikasikan di Penelitian RME, pmri. Tandai permalink.

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