Know the mass unit grams and kilograms.
Second, the teaching objectives
1. In specific life situations, let students feel and know the unit grams and kilograms of quality, and initially establish the concepts of 1 gram and 1 kilogram, knowing 1 kilogram = 1000 gram.
2. Let students know how to weigh objects with scales and make simple calculations.
3. On the basis of establishing the concept of quality, cultivate students' consciousness of measuring the quality of objects.
Third, the arrangement characteristics
1. Pay attention to provide students with familiar life situations according to their existing experience and help them understand knowledge.
The compilation of teaching materials strives to start from the familiar life situation of students, choose things around students and ask related mathematical questions; For example, the textbook introduces the quality unit by presenting the familiar life scene of students-shopping in the supermarket, stating that "the weight of goods can be expressed in grams or kilograms". In order to stimulate students' learning interest and motivation, let them feel the close relationship between mathematics and daily life.
2. Help students to establish the concepts of 1g and 1kg in various ways.
Gram and kilogram are two basic units of mass. If students have a vivid representation of the actual "size" of these two units, they can be used to estimate or measure correctly, and it is easy to grasp the progress between units. Conversely, students can further deepen and consolidate the concepts of these two quality units in actual measurement activities. The unit of mass is not as intuitive and concrete as the unit of length, so it can't be observed with eyes, and can only be perceived by muscle feeling. In order to achieve this mutual promotion effect and help students to establish the concepts of 1 g and 1 kg, some measures have been taken in the textbook.
(1) Help students to establish the representations of 1g and 1kg through activities. For example, with the help of a 2-cent coin and a bag of 1 kg salt, let students weigh by hand and feel the weight of 1 g and 1 kg; Ask the students to name an object that weighs about 1 kg, and help them to establish the representations of 1 g and 1 kg.
(2) Provide students with the opportunity to measure actual objects. For example, it says "If you want to know the weight of an object, you can use a scale" and introduces some commonly used scales to let students know about measuring tools. For another example, ask students to weigh all kinds of items brought from home. After knowing some different scales, let them practice reading out the values of commonly used scales, such as disk scales and spring scales, so as to enrich the experience of actual measurement and consolidate the concept of weight.
(3) Cultivate the awareness of estimation. For example, after students establish the concepts of 1 g and 1 kg, they are provided with the practice of estimating first and then measuring, so that students can compare the differences between the estimated results and the actual measured results, and thus correct their own estimation strategies.
Fourth, the specific content.
1. Theme map.
On page 85 of the textbook, quality units are drawn from the life scenes that students are familiar with. In teaching, teachers can start from students' existing experience and let students talk about where grams and kilograms are used in daily life, thus stimulating students' interest in learning.
2. Understanding of grams and kilograms.
To know the quality unit, students should not only know the name of the quality unit and the progress between units, but more importantly, understand the actual weight of each unit and be able to apply it in practice. Therefore, we should pay attention to let students know the approximate weight of 1g and 1kg through practical activities such as weighing, comparison and measurement, so as to initially establish the concepts of 1g and 1kg.
3. Understand the common scales.
Page 86 of the textbook introduces some commonly used scales. Teachers can prepare some commonly used scales according to the actual situation, such as scales, disk scales, electronic scales, spring scales and so on. Let students know that there are all kinds of scales in life that can help us know the weight of goods. Let the students talk about where they have seen these scales in their daily life, so that they can feel the close relationship between mathematics and daily life. Then let the students know about these tools and practice reading the values on the ruler. But be careful not to be too demanding, as long as students can read a whole ten, a whole hundred and a whole kilogram.
Solve the problem.
On page 87 of the textbook, choose the things around students and let them ask relevant math questions. In teaching, teachers can design lively and interesting mathematics teaching activities in combination with students' real life. For example, ask students to investigate the quality and quantity of apples and eggs bought at home and calculate how much apples weigh 1 kg and how much eggs weigh 1 kg. Students can also put forward some calculation problems according to the materials given in the textbook. Enable students to deepen their understanding of grams and kilograms in vivid and concrete situations.
5. Cultivate students' awareness of estimation.
After students establish the concepts of 1 g and 1 kg, teachers should provide students with the practice of estimating first and then measuring. For example, in the second question "Do" on page 87 of the textbook, the teacher can ask the students to do it in groups. When working in groups, show the items brought by everyone in turn, let each student estimate and record them first, then choose a suitable scale to weigh them, compare the differences between the estimated results and the actual measured results, and constantly revise their estimation strategies.