Comparing Lengths

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Comparing Lengths

You and your friend made paper airplanes today! Now you can't wait to see how they fly. But first you want to measure your planes to see whose paper plane is longer. In this text for KS1 you can learn about how to measure and compare lengths so that you can determine which plane is longer.

Comparing Lengths – Measuring

When we compare the length of two objects, we are finding the difference between how long they are. They can be longer, shorter or the same. We can subtract the two measurements to find the difference in length.

To compare the lengths, we will need to use a standard unit of measure, like a centimetre (or cm), and a special tool, like a ruler.

First, we will measure the length of this piece of paper by lining it up along the ruler and recording eleven cm.

Next, we will measure the length of this tape by lining it up along the ruler and recording four cm.

Comparing Lengths – Subtracting Equation

Then, we will set up our subtraction equation using the measurements. Larger measurement minus smaller measurement equals the difference. So we write eleven minus four equals.

Now we can solve and label our answer with the correct unit, cm.

Eleven minus four equals seven, so the answer is seven cm. We can say that the paper is seven cm longer than the tape or that the tape is seven cm shorter than the paper.

Comparing Lengths – Summary of Steps

When you need to compare lengths, find a ruler indicating a standard unit of measure, like inches or centimetres. Then all you need to do is the following:

Step # What to do
1 Measure the length of both objects.
2 Write the subtraction equation: Larger
measurement minus smaller measurement
equals the difference.
3 Solve the equation and label the answer with the correct
unit of measurement.
4 Now you can state the comparison: object A is
blank inches/centimetres longer or shorter
than object B.

Have you practised yet? On this website, you can also find interactive exercises for comparing lengths as well as worksheets and further activities.

TranscriptComparing Lengths

Freddie and Zuri made paper planes today! They can't wait to see how they fly. But first they want to measure them to see who’s paper plane is longer. Let's help them by learning about comparing lengths. When we compare the length of two objects, we are determining the difference between how long they are. They can be longer, shorter or the same. We can subtract the two measurements to find the difference in length. To compare the lengths, we will need to use a standard unit of measure, like centimetres, and a special tool, like a ruler. Let's start by making sure we are using the correct side of the ruler. We know we are on the centimetres side if we can see the cm mark. First, we will measure the length of this piece of paper by lining it up along the ruler and recording eleven centimetres. Next, we will measure the length of this tape by lining it up along the ruler and recording four centimetres. Then, we will set up our subtraction equation using the measurements. Larger measurement minus smaller measurement equals the difference. So we write eleven minus four equals. Now we can solve and label our answer with the correct unit, centimetres. Eleven minus four equals seven, so the answer is seven centimetres. We can say that the paper is seven centimetres longer than the tape or that the tape is seven centimetres shorter than the paper. Now that we have compared our first two objects, let's help Freddie and Zuri with their paper planes. This time, let's flip the ruler over and use the side marked centimetres. It doesn't matter which side we use as long as we measure both objects we are comparing with the same unit. First, we will measure the length of Freddie's plane and record twenty one centimetres. Next, we will measure the length of Zuri's plane and record thirty centimetres. Then, we will set up our subtraction equation using the measurements. Remember, the larger number goes first, so we will write Zuri's measurement, thirty minus Freddie's measurement, twenty-one, equals. Now we can solve and label our answer in centimetres. Thirty minus twenty-one equals nine, so the answer is nine centimetres. We can say that Zuri's plane is nine centimetres longer than Freddie's or that Freddie's plane is nine centimetres shorter than Zuri's. Before we see if their planes can fly, let's remember! Today we learnt about comparing lengths! When we compare the length of two objects, we are determining the difference between how long they are. Using a ruler and standard unit of measure, like inches or centimetres, first, measure the length of both objects. Then, write the subtraction equation: Larger measurement minus smaller measurement equals the difference. Finally, solve and label the answer with the correct unit of measurement. Now you can state the comparison, Object A is blank centimetres longer or shorter than object B. "I guess the length of our planes doesn't really matter, Freddie." "Yeah, they both fly really well!" "Ouch!"

Comparing Lengths exercise

Would you like to apply the knowledge you’ve learnt? You can review and practice it with the tasks for the video Comparing Lengths.
• Which paper aeroplane is shorter? Which is longer?

Hints

We can use the measurements noted on the rulers to tell which paper aeroplane is longer and which is shorter.

The longer paper aeroplane will have a larger number as the measurement. The shorter paper aeroplane will have a smaller number as the measurement.

Solution

If you said that the blue paper aeroplane is shorter and the red paper aeroplane is longer, you are correct!

If we look at the lengths measured by the rulers, we will see that the blue aeroplane is four inches long and the red aeroplane is ten inches long. Since the red aeroplane measurement is bigger, the red aeroplane is longer than the blue aeroplane.

• What do you know about comparing length measurements?

Hints

Remember, we already know the lengths of objects after we have measured, so that can't be one of the answers.

Use the image here to help visualise the formula.

Solution

When trying to find the difference in length between two objects, the larger length measurement minus the smaller measurement equals the difference in length. Then, we can use phrases like "Object A is smaller than Object B" or "Object B is larger than Object A" to describe the difference in length.

• Comparing leaves.

Hints

The longer object will have a larger number as its measurement.

Solution

The longer leaf is the orange leaf, because it has a length of 5 inches compared to the length of the green leaf (2 inches). The difference in length was calculated using the larger measurement - smaller measurement = difference formula:

5 inches - 2 inches = 3 inches

So, the orange leaf is 3 inches LONGER than the green leaf.

• What is the best description of the length comparison?

Hints

Use the image pictured here to help you find the correct difference in length.

Remember, the red pencil is LONGER than the blue pencil.

Solution

Using the image, you were able to complete the following problem:

22 centimetres - 17 centimetres = 5 centimetres difference in length

While many of the statements LOOK very similar, we know that the red pencil is the larger object and the difference in length is 5 centimetres. So, the correct statement is the red pencil is 5 centimetres LONGER than the blue pencil.

• What is the difference in length?

Hints

Remember, the formula to use is the larger measurement minus the smaller measurement equals the difference in length.

The larger measurement in this case is 10 inches and the smaller measurement is 6 inches.

Solution

When we look at both of these objects, the red plane is 10 inches long and the blue plane is 4 inches long. Using that information, we can use the formula pictured here to find the difference in length:

10 inches - 4 inches = 6 inches

So the red paper aeroplane is 6 inches longer that the blue paper aeroplane.

• Can you compare the length of the pens?

Hints

Remember to use the formula pictured here to figure out the difference in length.

Be careful as you read each sentence to decide which is the correct comparison. We can describe the objects as longer and shorter than the other.

Solution

When looking at the measurements on the rulers, we can see that the purple pen is 14 centimetres long and the black pen is 9 centimetres long. So the purple pen is the longer than the black pen.

14 centimetres - 9 centimetres = 5 centimetres

So, the sentence that best compares the length of the purple and black pens is: The black pen is 5 centimetres shorter than the purple pen.