How Big Is A Foot?

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Objective

SWBAT understand that a foot is 12 inches and to estimate objects that are about 1 foot in length.

Big Idea

Do students have any idea of what a foot really is? We will work to find out in several different ways.

Warm Up

10 minutes

To prepare students to add and subtract measurements of about 12 inches I give students some math problems to solve quickly. I read them out loud, give them 10 seconds to solve the problem in their math journals, and then move on. At the end we correct the problems together. I want students to increase their automaticity with math facts (2 OA.B.2). I remind students that they can be practicing math facts at home each night to improve their speed using IPAD math, flashcards or the math fact practice sheets that I send home each week for homework.

8 + 4 =

6 + 6 =

12 - 9 =

12 - 7 = 

10 + 2 =

12 - 4 = 

12 + 1 = 

12 + 10 =

18 - 12 =

5 + 7 =

The King's Foot

5 minutes

I show students the video, "How Big is a Foot?"

This video is a story about a king who wants to make a bed for his wife but he measures it with his foot. The builder has a different sized foot so the bed is not big enough for the queen.

At the end of the video I ask students why the bed was the wrong size? How might the problem have been avoided? We discuss the need for a standardized measure and in our country we usually use feet and inches. 

Does anyone remember how many inches equal a foot?

Today we will work with inches and feet.

Prediction

5 minutes

I begin today by asking each child to use their hands to show me about how big a foot is. I do not correct anyone here, but just look at their current estimates.

I pass out white boards and markers.  I ask students to look around the room and make a list of 5 things that they think are about 1 foot long. I do not take out rulers at this point because I am looking to see if they have any understanding of the concept of a foot.

Each child records his/her own 5 things that we will measure next. 

The Tools and the Measuring

20 minutes

I bring out a ruler, a yardstick and a 60 inch tape measure. I ask students to decide which of the three they think would measure exactly a foot from end to end. (I ask them to think in their heads and record their answer on their white boards with the 5 objects.)

Once everyone has decided, I have a student come up and show which tool they chose and to tell us why. We work together to find that a ruler has 12 inches which is also called 1 foot. 

Next I give each child a ruler and ask them to go and measure the objects they thought were a foot tall. They do not need to tell the exact inches at this point, but to say if it is exact, close, or not close to one foot in size. I tell them to put a check mark next to the name of the object if it is close to a foot, and an x if it is not. I demonstrate close and not close by holding up a few objects from my desk and say, if it measures 10 or more inches that is close, as long as it is less than the size of my hand bigger than the ruler on that end, but if it is more than a ruler and my hand long, or less than 10 inches in size, I say it is not close and mark an X. I know students hate to be wrong so I talk here about the fact that our first thoughts were guesses so it is ok to not have guessed right because now we are measuring. 

I give students about 8 minutes to do this.

I ring the bell and ask students to return to their seats. I ask if anyone found an object that was exactly one foot? I take raised hands, and ask a student to go show us with their ruler how their object is one foot long. We share about 5 objects. 

*Next I ask students to go back to one object that they found was less than a foot and find how tall it was to the nearest whole inch. We talk about if an object is in the middle how we move to the nearest larger inch and to record their findings on the white board next to the object. Before I let students go to measure I review starting at the zero point on the ruler. One purpose of this lesson is to help students choose the appropriate measuring tool (MP5), but more importantly I want students to learn to measure precisely, so starting at the zero point, and knowing what to do when an object falls between 2 inch marks, as well as thinking about close and not close in the early part of the lesson, are all encouraging students to attend to precision and to realize its importance to measurement (MP6). 

I ask for 3 people to share out their object and how many inches long it was. 

Next we talk about how we might measure something that is bigger than a ruler? We discuss using a yardstick, or a tape measure, but I ask what would happen if I only had a ruler? 

I hope that a student will suggest that you can add the measurements up so if it is a ruler and six inches I would 12 + 6 inches. 

When I feel that students understand how to measure by moving the ruler over, I ask them to go measure one object that they found that was more than a foot. I tell them it has to be one of their original objects.*

* If students do not have an object that was bigger or smaller, I will suggest something from around the room.

Closing

15 minutes

Students bring their measurements to the rug. Together we share some of the items that were bigger, smaller or exactly a foot in size. We work together to figure out how much bigger the items were than a foot. We also look at how much smaller some were.

Students take turns sharing an object and telling us how big it was. They ask how much bigger or smaller than a foot it was, and the rest of the students try to figure out the answer. 

We share 5 - 6 different examples.