Page 497 - Canadian BC Science 9

Science Skill 7
Estimating and Measuring
Measuring Length and Area
You can use a metre stick or a ruler to measure short distances. These tools are usually marked in centimetres and/or millimetres. Use a ruler to measure the length in millimetres between points A and F, C and E, F and B, and A and D. Convert your measurements to centimetres and then to metres.
AB CE
F
To calculate an area, you can use length measurements. For example, for a square or a rectangle, you can find the area by multiplying the length by the width.
4 cm
4 cm
Area of square is 4 cm 􏰁 4 cm = 16 cm2. 12 mm
18 mm
Area of rectangle is 18 mm 􏰁 12 mm 􏰀 216 mm2.
Make sure you always use the same units— if you mix up centimetres and millimetres, your calculations will be wrong. Remember to ask yourself if your answer is reasonable (you could make an estimate to consider this).
Estimating
How long will it take you to read this page? How heavy is this textbook? What is the height of your desk? You could probably answer all of these questions by estimating—making an informed judgement about a measurement. An estimate gives you an idea of the measure but is not an exact measurement.
Scientists often make estimates when exact measurements are not essential. You will find it useful to be able to estimate as accurately as possible, too. For example, suppose you wanted to know how many ants live in a local park. Counting every ant would be very time- consuming—and the ants would be most unlikely to stay in one spot for your convenience! What you can do is count the number of ants in a typical square-metre area. Multiply the number of ants by the number of square metres in the total area you are investigating. This will give you an estimate of the total population of ants in that area.
D
Science Skill 7 • MHR 479