Line Segment

Line and Line Segment:

Most of the shapes that we see around us are either made up of lines or curves. Various geometrical shapes are a combination of these. A one dimensional collection of points extending infinitely in either directions is a line and any portion of a line which has two end points is a line segment.

The above fig. represents a line segment with two end points A and B and is denoted as $\overline{AB}$. The length of a line segment can be varying and various methods are adopted to measure its length. To compare two or more line segments, a relationship between their lengths is established. Let us discuss these methods one by one.

1. Comparison by Observation

The most trivial method of comparison of two line segments is simple observation. Just by observing two line segments one can predict which is long or short compared to the other.

In fig. 2, by observation itself we can say that the line segment $\overline{CD}$ is greater in length as compared to the line segment $\overline{AB}$ . But this method has several constraints, every time we cannot rely simply on observation to compare two line segments.

2. Comparison using Trace Paper

With the help of trace paper two line segments can be easily compared. Trace one line segment and place it over on the other segment and it can be easily deduced which is greater in length. For more than two line segments repeat the process again and again.

For precise comparison, the line segments must be traced accurately. Hence this method depends on the accuracy of tracing which puts a limitation on this method.

3. Comparison using Ruler and Divider

There are certain markings on the ruler beginning from zero as shown in the fig. given below , these markings divide the ruler into equal parts. Each part is equal to a length of 1 cm and these unit centimeters are further subdivided into 10 parts and each sub-part is equivalent to 1 millimeter.

To measure a line segment $\overline{AB}$, place the zero marking of the ruler along the beginning of the line and measure its length accordingly.

In the fig. given above, the length of  $\overline{AB}$ is 8 cm.

To eliminate the positioning error we use a divider. Place one of the needles of the divider at A and other at B and then place the divider along the ruler and measure its length. This method is more accurate and reliable.