Measurement of Length
Length means how long something is. We see many things around us. Some are short in length such as paper clip, pencil, pen, notebook etc., some are long in length such as tree, electric pole, cloth, room, train track and some are very long such as distance between two places. We need to select suitable unit to measure these lengths.
Non Standard Units of Measurement
In early days body parts were used to measure length. But measurements taken by these means are not accurate and consistent. If we use our hand span to measure length, the measurement taken by different person will vary as our hand spans are not equal.
Example: a child hand span is smaller than the adult. So, hand span, hand, foot and cubit are not standard units of measurement.
Standard Units of Measurement
We observed that nonstandard unit of measurement does not give same results. So, we need to use some standard units for measuring lengths. Otherwise the measurements of an object will be different when measured in different ways. We use different units of length to measure different lengths.
Example: We measure length of table edge, length of chalk, length of pencil etc. in centimeters (cm), length of a room, height of tree, length of cloth, height of an electric pole etc. in meters (m) and longer distance such distance between two places in kilometers (km).
Points to be remembered
The standard unit of length is meter.
One meter is divided into 100 smaller units called centimeters.
So, 1m = 100cm
Short form of meter is “m”, centimeter is “cm” and kilometer is “km”.
1000 m put together to make a bigger unit called a kilometer.
1km =1000m
Instrument of Measurement of Length
We use metric ruler, metric stick, tape, rod etc. to measure length.
Word Problem
Example 1: Length of blue rope is 7m and length of red rope is 5m. Which rope is bigger and by how much?
Solution:
Example 2: Ria travelled 2km by car and 5 km by bus. How much distance did she travel in all?
Solution: