Explain what a centimeter is. Show that the section on the ruler from 0 to 1 is exactly one centimeter long. State that your thumb is about one centimeter wide. Show this with help from the ruler. Explain that you can estimate the length of objects by comparing it with the width of your thumb. This is because you already know that your thumb is about one centimeter wide. Explain that with an object that is larger than 10 cm, students can also use the distance from their thumb to the tip of their pointer finger. This makes it easier to measure the length of a table, for example. Next, have the students take an object, for example from their pencil case, and have them estimate the length of that object. Choose several of the students' objects and ask what they estimated and how they did that. Also ask what other students estimate that object's length to be. After students have given an answer, you can measure the object to find out which estimation was the closest. Next, you show a few statements on the interactive whiteboard. The students must answer whether each statement is true or false. Then the students must estimate how long an object is in real life. They can choose from a number of possible answers.
To check that students can estimate the length of objects in centimeters, you can ask the following questions:
- What is about one centimeter?
- How can you estimate the length of an object?