(EXCERPTS FROM)

1. OVERVIEW

   Students have experienced the measurement of weight such as at the time of physical health check-ups to measure their body weight. We should remind them of such experiences to introduce the concept of weight for the first time in this unit. Although weight is a quantity unable to be measured in a direct, visible way like length and size, have the students realize that they can use an arbitrary unit and find how many units there are to find weight just like in length and size. It should be done through actual measuring of concrete objects, then have them understand the usage of the units of weight such as “g” and “kg.”

   Like a clock, a scale has graduations along the curve on its surface. Students sometimes have difficulty reading the measures. Also, the fact that weight cannot be determined by the object's size nor texture makes it hard for the students to understand weight. Thus, it is important to allow them to experience many occasions of actually measuring the weights and getting familiar with the concept.

2. GOALS

   1. To understand the concept of weight.

   2. To understand the units of weight, “g” and “kg.”

   3. To be able to read a scale and measure various objects with a scale.

   4. To understand the relationship between “g” and

   5. To be able to add and subtract weight.

3. KEY POINTS OF INSTRUCTION

1. Concept and measurement of weight

   Although this is the first unit of formal instruction on weight, children have had previous experience with weight in daily life and in various routine activities such as physical examinations.

   Judging from outward appearance only, it is easier to estimate an object's length or volume than its weight. However, when determining weight, both indirect and direct approaches are possible: feeling the weight of the object in one's hands or placing it on a scale. It is also possible to numerically express an object's weight beginning with an arbitrary unit of measurement. A similar instructional method was outlined in the unit on Length and Measurement.

   These basic ideas are important not only in order for students to understand the concept of weight, but also for them to understand its measurement. As in the instruction of length and volume, there are four steps for the instruction of weight:

   1. Direct comparison;

   2. Indirect comparison;

   3. Measurement by an arbitrary unit;

   4. Measurement by a universal unit.

   Because weight is difficult to judge visually, it is important to focus on the necessity of a measuring tool. Students' subjective interpretations of weight (e.g., “heavy,” “light”) are replaced by the graduation indicated on measuring tools and visualized there. This leads to the introduction of a scale.

   A scale is constructed to capture the force of gravity on an object 's mass with visual movement. One example is associating an object 's weight with the lengthening of a spring. Another example is converting the weight into rotational movement, observing the weight in relation to the number of degrees a scale's dial hand moves. This idea of measurement is much more difficult for students to learn compared to the measurement of length or volume. For example, it is easy to visually grasp the sense of an object's length by using a measuring tape, because the increments shown on the flexible tape are the same as those on a graduated ruler. But using a scale, an object's weight is indicated more abstractly—by the degree a dial hand has moved—so it is harder to get the sense of how much it weighs visually.

   Because a balance scale makes it easier for children to understand the concept of weight and visualize the meaning of measurement, it is better to use a balance scale when first introducing the topic. However, because upperdish automatic scales are used more frequently in real life, it is also important that children learn how to use and read them accurately.

   As part of their study of the automatic scale, students in this unit will assemble several bags of sand with amounts such as 1 kg, 2 kg, and 3 kg. This is so that students are exposed to both the physical experience and actual measurement of standard weight.

2. Introducing the unit of weight

   There are three key points regarding the instruction of the weight unit.

   1. Weight can be expressed using the number of standard units; it can be numerically stated and labeled.

   2. It is more convenient to have two related units such as g and kg so that depending on the purpose one can determine the unit to use and can write the weight in simplest terms (e.g., 2 g rather than 0.002 kg).

   3. 1 kg is equivalent to 1000 times 1 g.

   Because children are not particularly good at converting between these units, and converting is not encountered so often in daily life, it is extremely important to emphasize the relation 1 kg=1000g.

   The minimum graduation of an upper-dish automatic scale with the capacity of 1 kg represents 5 g, and there are 200 of these increments shown on such a scale. It follows then, that if the minimum graduation were 1g there