# Comparing Lengths

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## Objective

SWBAT identify a standard and non-standard unit of measure and use these tools to compare the length of 2 objects.

#### Big Idea

Understand how to compare the lengths of various objects.

## Intro

5 minutes

Yesterday we did a lot of hard work finding the length of different objects and today we are going to build onto that. If I have 2 objects and I want to compare them, how would I do that?

I allow student to discuss what tools they would use to measure the lengths and how to find the difference (MP3). I ensure I emphasize why I would need to compare inches to inches and centimeters to centimeters.

There is one trick I think might help you as you begin to compare the lengths of objects, and you can use it whenever your ruler or the ruler used doesn’t begin measuring the item at 0. If I rush and I look only at where my object ends, I may not know the accurate length of the object. Let me show you what I mean.

I model measuring the 2 items based on the pictured ruler and draw attention to circling the beginning number and also the units. I explain that by looking at this I can find the exact length of the object because I understand where the measurement begins.

Now that I know the length of each object, what could I do to find the difference between the 2 objects?

## Guided Practice

10 minutes

Now I need you guys to help one another better understand this. I need someone to come and help me find the difference between the 2 things in each example, and to explain to us what tricks and tips you are using to figure this out.

I always call on students to explain what the student who is modeling at the board is doing, just to include more students into the activity (MP3). When they know that there is the chance they will be called on or that they might have the opportunity to come up and work at the board they pay closer attention and are more engaged in the activity.

## Practice

30 minutes

Today I am going to need you to build on what you did yesterday to compare the lengths of 2 objects. I have added more math tools to your bags and I have some picture cards in there as well. You don’t have to begin measuring each item at 0, but you do need to represent on your paper where you began your measurement just like we did on the board. If you begin measuring a cube at the 4 inch mark, that’s what I should also see in your picture (MP6). I want you to find and record the measurement of 2 objects in your bags and want to see you compare the measurements to find the difference between them. Remember how important it is to take your time because we do our best work when we focus and take our time!

Students will need to measure accurately, even when they don’t begin at the 0. For my higher performing students they enjoy a challenge like this, but for my lower performing students we will do a few of the measurements together in a small group before I send them back to work independently. I want to ensure they have concrete examples on their paper, in addition to the board, before they get started so that they have work to refer back to.

## Close

5 minutes

Great job today! You were able to find some cool differences between the items on your papers, and I saw you pushing yourselves to measure items beginning at other numbers than 0 and still finding the correct length! What did you guys realize when you didn’t start at 0? What things were you able to do to make sure your measurement was correct? How did you make sure you recorded the correct standard units you used? Why is that important?

I always try to close my lesson by having students share what they did and how they applied what we learned today to their practice. I want to reemphasize the critical importance of recording units used, because of how that impacts measurement.