Lines and Line Segments

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SWBAT identify and measure a line segment using the appropriate tool, recording their outcome using the correct units.

Big Idea

Common Core expectations for second grade are that students will be able to measure a line segment, record the length in appropriate units, and add and subtract to compare the lengths of the lines.

Warm Up

10 minutes

We start today by generating a list of measurement tools. I ask students to list all the tools they can think of to measure with. I record the answers on my computer projected on the White Board. (You can do this on a board or easel, but I want to be able to classify the list by the kinds of measuring it does ie length, weight, volume).

After students have given their ideas, I put the 3 headings on the board LENGTH, WEIGHT, VOLUME (LIQUID). I ask students one at a time to tell me where to place each tool. We discuss how different tools measure in different ways. This will set the foundation for measuring in this unit, and also open the discussion for appropriate units of measure, as well as selecting the appropriate tools for measurement (MP 5).

Teaching the Lesson

20 minutes

I want to help students understand the distinction between a line and a line segment. I start drawing a line across the board. I keep going to the end of the board. At the end of the board I pretend to continue my line along the wall. I ask students what I am making? (A line). I go back to the board and draw a short line with a dot at each end. I ask what I am making now? Most students will reply that I have made a line. I tell them that this is just a piece of a line. It has a special name, does anyone know what the name is? 

I show the students an orange that I have broken apart into segments. Does anyone know what the pieces are called? They are not the whole orange, but pieces with a special name. Does anyone know what the name is? I give hints using a "hangman strategy" where I put up S __ __ __ __ __ __S. We work together to fill in the missing sounds and get the word segments. I say that a segment is a piece of the whole. 

I return to my line segment. I point out that it is not as big as my first line it is just a piece so it is called a line ________________. (segment)

I tell students that today we will be measuring line segments. What tool do they think would be good for measuring line segments?  I help them work towards using a ruler, centimeter stick, meter stick or a yardstick. 

We talk about the unit we will measure with. We discuss inches, centimeters, miles, feet, and come to a decision about a unit that would measure a small length (inches or centimeters) and how we would record each one (in, or cm).

Measurement Practice

20 minutes

I tell students that today they will be measuring a series of line segments on a worksheet Line Segment Practice and then solving problems using those lengths. 

Before students begin I point out how the line segments on their papers have dots and letters at each end. A line segment is named by the points at each end. They will know which lines to compare by the letter names at each end. 

We practice identifying the lines on their papers by the letter names. When students are comfortable with this I explain the directions and ask them to work independently to measure the lengths of the lines to the nearest inch and then to answer the questions at the bottom of the page. Using Line Segment Distances to Solve Addition and Subtraction Problems

I circulate around supporting the students who may need help. 


10 minutes

When students complete their papers, I ask them to report out on the sizes of the lines, and how they solve the problems presented (MP1). Students are reminded that as their peer shares, they look at his/her own work to see if their answer matches the answer of others, or if they have a different answer.

If their answer is different, we share the solutions and work together to decide which answer fits the problem that is presented.

Students learn from correcting their own work. They can see if their strategy worked, they can see other strategies, and they can develop new strategies for similar problems that they may face in the future.