# Measuring lengths in centimetres

##### Class practical

Practice at measuring and estimating lengths.

#### Apparatus and materials

For each student group

Paper scale

Sticky tape or glue

#### Health & Safety and Technical notes

Prepare a paper scale by photocopying a metre rule in sections of 25 cm. (Check that the photocopier is giving true 100% reproduction.) From this, make a master sheet with sections 0-25 cm, 25-50 cm, 50-75 cm, 75-100 cm. You should be able to fit two of these on an A4 sheet of paper.

Students can then cut strips, glue them end-to-end, and make a 2 m rule.

#### Procedure

a The sheet gives a paper ruler marked in centimetres. Cut out the sections and stick them end-to-end. (Make sure that the ends meet accurately.)

b Make some measurements with your tape and record them. Here are some suggestions:

• width of your foot where it is widest
• height of a neighbouring boy or girl (record their age)
• height of a parent or other adult
• width and height of your front door
• length and width and thickness of a book
• length of an egg
• the length, width and height of a room in your house (or your classroom): write each of them down in centimetres, then in metres. Work out the volume of the room in cubic metres.
• diameter of a clock face
• diameter of a watch face
• diameter of a drinking glass and its circumference. Then divide the circumference by the diameter to find a rough value for π.
• your own diameter (at waist)
• the difference in height between two people (such as father and mother, two sisters, or two other students in your class)
• the circumference of your upper arm, round your biceps muscle, first when your arm is slack, then when you are holding a heavy load, with your arm bent up at the elbow.

c After you have made two or three measurements, draw up a table with three columns headed as shown. In the first column, state the length you are measuring. In the second column, write an estimate of the length in centimetres. In the third column, write the measured value.

#### Teaching notes

1 Students will be familiar with the use of the metric system of length measurements. This is a time to measure varying lengths, first of all with a ruler and then with many other kinds of length-measuring devices, such as vernier calipers, micrometers and sonic distance measurers.

2 Students should be able to estimate lengths and then check to see how accurate their estimates have been. Encourage them to make an estimate before measuring each length. Checking the table of estimates and measurements may reveal whether their ability to estimate is improved by this exercise. The table can also be checked to see if students find it easier to estimate large or small lengths.

3 Students can make a ruler from paper. Download an example and photocopy it so that the scale is correct.

This experiment was safety-checked in July 2007