Estimating Lengths in Metric Units

Transcription

1 Estimating Lengths in Metric Units Overview This activity introduces the idea of using our own parts of the body, such as hand spans and arm lengths, as personal references or benchmarks for estimating lengths in metric units. In this enjoyable activity students work in pairs and gain practice at both estimating and measuring with rulers and tape measures. It also introduces the guess, estimate and measure activity model that can be adapted for many other types of measurement. This encourage students to think metric, rather than always trying to convert from other systems of measurement they may be more familiar with. Skills and Knowledge Preparation and Materials Metric units of length - m, cm, mm Estimating lengths Measuring with tapes and rulers Counting in 10s and 20s Tape measures (1 per pair of students) Photocopy Activity Sheets 1 & 2 (1 per student) Photocopy Practice Sheet 1 (2 per student) Suggested Procedure Step 1: The challenge Ask: Take a piece of paper and try drawing a line that you think is approximately 10 centimetres long. Don t looking at any ruler or tape measures. Just draw what you think it might be. Distribute tape measures and ask students to measure their lines. Ask: How did you make your estimate? How close were you? Did anyone guess much too long? Did anyone estimate much too short? MEASUREMENT ESTIMATING LENGTH IN METRIC UNITS Page 1 of 8

2 Explain to students: Don t worry if your first estimate was not so good. I will teach you a way to make better estimates. At the end of the session you will be much improved. Step 2: The body references The 10 cm hand width It is possible to find a good set of measures by using your own hands. Can anyone suggest a part of their hand that might be about 10 cm? Demonstrate how to lay the palm of the hand across a ruler to find a 10 cm measure. Each person should find their own exact 10 cm. It will be different for each person: some may need to include their thumb, some may not. Note: This is the traditional hand used for measuring the height of horses. In British Imperial units it was 4 inches. Distribute Activity Sheet 1 and get students to mark their own measure on the diagram. Demonstrate how this can be used as a measure by counting in 10s. For example: 3 hands = cms It was important to find the measure that was exactly 10 cm not 8 or 9 cm because it is easy to count in 10s. This way of measuring can be very useful in many situations. For example: for estimating the size of kids clothing for spacing seedlings when planting for deciding whether furniture or kitchen things will fit into spaces in your house. The millimetre alternative For students who will be learning trades related to the building industry it may be more useful to do this exercise in millimetres rather than centimetres. Ask: What would this 10 cm be if we measured it in millimetres? Make sure that they all know that: 1 centimetre = 10 millimetres So 10 cm = 10 lots of x 10 mm = 10 x 10 = 100 mm MEASUREMENT ESTIMATING LENGTH IN METRIC UNITS Page 2 of 8

3 Ask them to write the millimetre lengths onto their diagrams and to do this for all of the subsequent measures as well. Other body references Introduce the other body references shown on the sheet one at a time. For example, ask: Experiment to find one finger on your own hand that is exactly 1 cm. You may need to turn one sideways if you have wider fingers. Make a note on your own sheet. Now experiment with the hand span (stretch out as far as you can) -is it a bit more than 20cm -is it a bit less than 20cm Demonstrate to the students how to measure and count in 20s. For example: 4 hand spans (stretched) = cms It is important to use 20 for counting not 19 or 21 because it is easy to count in 20s. If you have a span that is a little shorter than 20 then you should count in 20s and at the end take off a few centimetres to compensate. If your span is longer than 20 you should adjust by adding a few centimetres to your estimation. Get students to try this out for themselves. The one metre measure Finally discuss the one metre measurement. This can usually be taken from one shoulder towards the end of the other arm when outstretched. Depending on the length of each student s arm this will be from the shoulder to the wrist, the knuckles or the fingertips. Ask all students to find their horizontal metre this way before moving on to the vertical metre. MEASUREMENT ESTIMATING LENGTH IN METRIC UNITS Page 3 of 8

4 The vertical metre is from the floor to the waist, of the hip, or the trouser pocket, depending on one s height. This is useful for estimating vertical heights such as when buying furniture, since the shoulder-arm measure is not much used in this situation. Step 3: Using the body measures to measure each other Arrange students in pairs. Give each pair a copy of Activity Sheet 2. You will be measuring each other in this activity You will do this in 3 stages: Stage 1 Guess with your eyes - then fill in the guess on the table in the guess column. Stage 2 Estimate a measurement using your hands and arms - then fill in the estimate in the estimate column. Stage 3 Measure accurately with the tape measure - then fill in the exact measurement in the last column. The items on the Activity Sheet are designed to create maximum interaction between students and usually lead to much laughter as well. They also introduce language of measurements such as, circumference, height, distance. As students are doing the activity circulate and encourage them to use the appropriate measures and give hints where necessary. For example: For measuring heights it is easier to stand against the board or a wall and make a mark. When using a tape measure make sure you start at the zero mark, rather than the end of the tape. MEASUREMENT ESTIMATING LENGTH IN METRIC UNITS Page 4 of 8

5 Debriefing the activity When students have completed the activity explain the final task: Let s see who has improved at estimating. I want you to use your new estimation skills to draw a 15 cm line. Do it without looking at a ruler or tape. But you can use your body and hand measures. When students have done this ask: Who thinks they are now better at estimating? Extension Practising these techniques at home will help you to remember them. It is also really useful to teach them to someone else. Distribute copies of Practice Sheet 1 (2 copies) and explain the task to the students. Encourage them to do the task at home with a friend or family member and to report back in a following session. MEASUREMENT ESTIMATING LENGTH IN METRIC UNITS Page 5 of 8

6 Estimating lengths in metric units Activity Sheet 1 These hand measures are useful references for estimating small lengths ß 10 cm à ß 20 cm à Longer lengths can be estimated using these two different body metre meaures MEASUREMENT ESTIMATING LENGTH IN METRIC UNITS Page 6 of 8

7 Estimating lengths in metric units Activity Sheet 2 Body references for measuring length Work in pairs to make these measurements and fill the answers in the spaces of the table Guess Using eyes only Estimate Use hands and body measures Accurate Measurement Use tape measure Your partner s height The circumference of your partner s head Your partner s foot length The distance between your partner s eyes MEASUREMENT ESTIMATING LENGTH IN METRIC UNITS Page 7 of 8

8 Estimating lengths in metric units Practice Sheet 1 Estimating metric lengths at home Teach the hands and body references for metric length to a friend or family member. Give them a copy of Activity Sheet 1 to record their own body measures. Choose 5-8 different things that you will both to measure. These could include: Sizes of furniture e.g. length of dining table, height of chair, width of kitchen bench. Lengths in the house e.g. height of doors, width of hallway, length of room. Other parts of the body e.g. neck circumference, arm length, back length. Each take a copy of the table below and write in the things you have chosen. Remember the procedure: First Guess using eyes only. Then Estimate using hand and body references. Then Measure using a tape measure. Object or distance Guess Estimate Measure Make notes about how you both went with your estimations: Did you get better? Were you a good teacher? Which estimations were most difficult? MEASUREMENT ESTIMATING LENGTH IN METRIC UNITS Page 8 of 8