Class 6 Maths Understanding Elementary Shapes Measuring Line segments

Measuring Line segments

A line segment is a fixed portion of a line. The length of a line segment can be measured because it has two endpoints.

In the above figure, the length of the line segment is simply written as AB.

The length could either be determined in Metric units (e.g. millimeters, centimeters or meters) or Customary units (e.g. inches or foot).

We can measure a line segment by two ways:

• With the help of scale or ruler only.
• With the help of a pair of dividers and a scale or ruler.

We can compare any two line segments in several ways:

Comparison by Observation

We just look the line segments and then see which one is larger.

Here, line AB is larger than line CD.

But we cannot always be sure about our usual judgment.

Here, we cannot measure which line is larger. So, we need better methods of comparing line segments.

Comparison by Tracing

To compare AB and CD, we use a tracing paper, trace CD and place the traced segment on AB.

This method is also difficult because we cannot trace the lengths every time we want to compare them.

Comparison using Ruler and a Divider

A ruler is divided into 15 parts and each of the 15 parts is of length 1 cm. Again each centimeter is divided into 10 subparts and each subpart of the division of a cm is 1 mm.

Let we want to find the length of a line segment of 3.5 cm.

Place the zero mark of the ruler at A. Read the mark against B. This gives the length of AB.

Now, Length AB = 3.5 cm.

Problem: Draw any line segment, say AB. Take any point C lying in between A and B. Measure the lengths of AB, BC and AC. Is AB = AC + CB?

Solution:

Consider a line segment AB of length = 8 cm.

Now, mark a point C at AC = 5 cm

Measure CA.

We see that the length of CA = 3 cm

i.e. AB = AC + CB

Therefore, for any point C lying in between A and B on the line AB, the above is true.

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