Comparing the Lengths of Objects

Learning how to compare the lengths of objects is a second grade, Common Core math skill: 2.MD.4. Below we show two videos that demonstrate this standard. Then, we provide a breakdown of the specific steps in the videos to help you teach your class.

Prior Learnings

Your students will have learned how to measure objects through non-standard units, like using paperclips to measure a pencil (1.MD.1). They should also be able to compare objects using terms like longer, shorter, longest, and shortest (1.MD.2). 

Future Learnings

In the future, understanding how to measure objects with a ruler will help your students expand on and apply the concept elsewhere. Students will be able to make a line plot, measure objects, and place those measurements on the plot (2.MD.9). Your students will also be able to use rulers marked with halves and fourths of an inch (3.MD.3) and apply “linear measurement to measure perimeter and area” (3.MD.5- 8).

Common Core Standard: 2.MD.4 - Measure to determine how much longer one object is than another

Students who understand this principle can:

1. Select the appropriate tool to measure an object’s length.
2. Compare two measurements by finding their difference in length.
3. Explain how many units longer one object is than another object. 

2 Videos to Help You Teach Common Core Standard: 2.MD.4

Below we provide and breakdown two videos to help you teach your students this standard.

Video 1: Comparing Object Measurements

‍This video demonstrates how to measure objects using a ruler and then compares them, finding the difference between them.

First, the video starts by explaining that length-measuring tools can be used to see how long an object is. Common measuring tools include 1) rulers, 2) yard sticks, 3) meter sticks, and 4) measuring tape.

There are two different systems of measurement, each has their own units:

1. Metric
   a. Centimeters - cm
   b. Meters - m
   c. Kilometers -km
2. Customary
   a. Inches - in
   b. Feet - ft
   c. Yards - yd
   d. Miles - mi
   

After, the video shows how to use a ruler to compare the length of a red pencil and a blue pencil. Since rulers measure objects in inches, then students will use inches in their answers. 

How to measure the length of the pencils:

1. Align the end of the pencil with the number 0.
2. See how far it goes.
3. The tip of the red pencil reaches the number 4.
   a. The red pencil is 4 inches long.
4. The blue pencil is aligned with the number 0.
5. The tip reaches the number 6.
   a. The blue pencil is 6 inches long.
   

How to compare the length of the pencils:

1. The blue pencil is 6 in. and the red pencil is 4 in.
2. 6 is 2 more than 4, so the blue pencil is 2 in. longer than the red pencil.
   

The second example compares the length of two cars, using a measuring tape (in meters). The video explains that 1 meter is about 3 feet.

The video shows how to measure the car’s using the meter tape, following the same method used when measuring the pencils.

1. The black car is 5 meters long.
2. The wgite car is 6 meters long.
3. 6 is 1 more than 5.
4. So the white car is 1 meter longer than the black car.
   

Video 2: Different Ways to Compare Length

‍The video starts by stating that one of the most important ways we use measurements is by comparing the length of one object to another. It then poses a question: How can you figure out if your new car can fit into your garage?

To find out, you need to compare the lengths, and to compare their lengths, you need to know the length of each object separately. In this instance, you need to know the length of the car and the length of the garage.

If the length of the car is greater than the garage, then it won’t fit. The video then gives different methods to compare object lengths.

1. Counting on from one number to the next.
   a. The car measures 16 ft; the garage is 12 ft.
   b. If one counts on from 12: 13, 14, 15, 16…
   c. One sees it took 4 numbers to get to 16.
   d. So the car is 4 feet longer than the garage.
2. Another method is subtraction.
   a. The car measures 15 ft; the garage is 18 ft.
   b. 18 - 15 = 3
   c. This means the garage is 3 feet longer than the car.
   

The car fits into the garage in the second example.

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*Information on standards is gathered from The New Mexico Public Education Department's New Mexico Instructional Scope for Mathematics and the Common Core website.