Lesson 2. Measuring Length

Transcription

1 Math 5 Lesson 2 Measuring Length How Big is My Desk? Daksha needed to measure the length of his desk, but he did not have a ruler. He decided to use the width of his hand instead. He laid each hand side by side, moving them all the way across his desk. He counted each hand as he laid it on the desk. Daksha s Desktop Length of Desk Daksha found out that 8 of his hands would fit across his desk. Math 5 3-7

2 Reflection Do you think that all of the students in his class would get the same answer? Why or why not? Objectives for this Lesson In this lesson you will explore the following concepts: Use personal referents to measure length for the unit mm Measure in millimetres Describe the relationship between mm and cm units Measuring with Objects You can measure with many objects. The pencil is 3.5 Loonies long. The pencil is 3 paperclips long. 3-8

3 Example 1 What is the length of the remote control in paperclips? Simply count the paperclips: 6.5 paperclips is the length. Go online to complete the Concept Capsule about Measuring Length, Width, and Height with Rulers. Measuring with Standard Units Daksha used his hand to measure his desk. Reflection Why do you think that will not always work? Math 5 3-9

4 If Daksha is 10 years old now, how do you think the measure of his desk today will compare to a measure taken 10 years from now? Daksha s Age Desk in Hand Units ? What if Daksha isn t around and you need to know the length of the desk? Is it 8 of your hands long? It probably isn t. In Egyptian times they used body measures as standard units. Standard means that if they were trading with another country they would all use the same measure. Today the metric system is used for standard units. 3-10

5 One of the units you can use to measure the length of objects is the millimetre. This is a metric unit. The millimetre is the smallest unit on a metric ruler. On this metric ruler the numbers mark centimetres. The small marks are millimetres. centimetre mark millimetre mark You can use the millimetre to measure small objects. You may also use them when a very accurate measurement is needed. The abbreviation for millimetre is mm. The thickness of a Loonie is about 1 mm. 1 mm 1 cm As you can see, centimetres are larger than millimetres. Each centimetre equals 10 millimetres. The abbreviation for centimetre is cm. 10 mm = 1 cm Math

6 If you know that 10 mm = 1 cm you can conclude that 20 mm = 2 cm. Every time you see a number on the metric ruler it means a number of centimetres. Simply put a zero after the number and you have the number of millimetres. To measure a small item you should line it up with the end of the ruler or the first mark of the ruler. Example 2 How long is the pencil in millimetres? In the picture, the point of the pencil is after the 6 on the ruler. That means the pencil is at least 60 mm. There are 6 more marks before the end of the pencil. It is marked in blue here. That means 6 mm. Put that together to get millimetres or 66 mm. You can measure objects in both centimetres and millimetres. Some objects are very small and should be measured in millimetres. If an object is smaller than a centimetre you should use millimetres only. If it is larger than a centimetre you can use either. 3-12

7 Now It s Your Turn What unit would you use to measure the following objects? Centimetre or millimetre? a. the diamond in a ring b. a cell phone c. height of an action figure d. a dry lima bean Solutions a. mm b. cm c. cm d. mm Let s Explore Exploration 1: Measuring Small Objects Materials:, Lesson 2, Exploration 1 page from your Workbook, Metric ruler, Five assorted small objects, Pencil, Paper Math

8 1. Use your ruler to measure your hand like this: 2. Record the measure in millimetres and in centimetres in the table provided. 3. Use your ruler to measure your hand like this: 4. Record the measure in millimetres and in centimetres in the table provided. 5. Measure your finger like this: 3-14

9 6. Record the measure in millimetres and in centimetres in the table provided. 7. Measure each of your five assorted small objects in both millimetres and in centimetres. Record each measure in the table provided. 8. Compare your measures to those of a friend. Are the measures the same for your hands? 9. Are the measures the same for your objects? 10. Compare the millimetre measure to the centimetre measure. How are they the same? How are they different? Metre Sticks A metre stick is marked the same as a metric ruler. The difference is that it will go all the way to 100 centimetres. This means when you look at a metre stick you are seeing: 1 metre 100 centimetres millimetres Math

10 Measuring with a metre stick is done just the same as measuring with a ruler. You may not want to pull it out to measure a paperclip. If you are measuring your desktop or your height it would work better than a ruler. You can measure objects with a metre stick. Use the exploration to find the measures of things in your environment. Let s Explore Exploration 2: Measuring Large Objects Materials:, Lesson 2, Exploration 2 page from your Workbook, Metre stick, Pencil, Paper Measure the width of the door in the room you are in. That means this way. 1. How many centimetres wide is the door? 2. How many millimetres wide is the door? Measure the window in the room. Record how tall it is. 3. How many centimetres tall is the window? 4. How many millimetres tall is the window? 3-16

11 Find two objects in the room that you are in that are about 1 metre or less. Use the metre stick to measure the object and find the exact measurement. 5. How many centimetres is the first object? 6. How many millimetres is the first object? 7. How many centimetres is the second object? 8. How many millimetres is the second object? 9. How do your measurements compare to those of a friend? 10. How do your millimetre measurements compare to your centimetre measurements? Example 3 What would you use to measure each object: a metre stick or a ruler? A. rug B. marble C. watch face D. your height Think: Is the object smaller than a ruler or larger than a ruler? Smaller than a ruler: marble and watch face Larger than a ruler: rug and your height A ruler would be used to measure objects that are smaller. Use a metre stick for anything larger. The answers are: A. metre stick B. ruler C. ruler D. metre stick Math

12 Let s Practice Turn in your Workbook to, Lesson 2 and complete 1 to