Comparison of Line Segments
Comparing two line segments means finding the shorter or longer line segment. The methods that compare the length of line segments are as follows:
Comparison by observation
Figure shows two line segments AB and CD.
Just by observing them we can easily find out that line segment CD > AB. But it is not always possible, if the difference between their lengths is very small.
Comparison by using a divider
Divider is a geometrical instrument which has two arms hinged together with the help of a knob at one end. The other ends of the two arms have metallic needles. To compare the given line segments AB and CD, we place the needle of one hand of the divider at point C and open its other arm carefully so that the needle of the other arms falls at D.
Now, lift the divider carefully so that the opening of the two arms remains unchanged. Place one of the needles at A of line segment AB and the other arm is free to fall at any point on AB. Now, there are three possibilities.
- The other arm falls exactly at B, then AB = CD.
- The other arm falls between A and B, then AB > CD.
- The other end falls away from B, then AB < CD.
Comparison by Tracing
We can also compare line segments AB and CD by the tracing method. Trace one of the line segments, such a way that point C of traced segment CD coincides with the point A of the line segment AB. By doing so, we observe the following.
Measurement of line segments
A line segment is a part of a line. It has two end points and has a definite length, no breadth, and no thickness. The length of a line segment is a dis¬tance that can be measured in metres, centimetres, millimetres, etc.
10 (millimetres) = 1 cm (centimetre)
10 cm (centimetres) = 1 dm (decimetre)
10 dm (decimetres) = 1 m (metre)
10 m (metres) = 1 dam (decametre)
10 decametres (dam) = 1 hectometre (hm)
10 hectometres (hm) = 1 kilometre (km)
To measure line segments, we use a scale that has centimetre marks on one edge and inch marks on the other edge. Observe that each centimetre is divided into 10 equal parts and each part is called a millimetre (mm).
To measure the actual length of a line segment AB with the help of a scale, we place the scale along AB in such a way that 0 mark on the scale coincides with point A, and mark 5 coincides with point B of the line segment AB.