Measuring the length of a curved line

Concept  of rest and motion
(a)     Rest :
An object is said to be at rest if it does not change its position with respect to its surroundings with the passage of time.

(b)     Motion : 
A body is said to be in motion if its position changes continuously with respect to the surroundings (or with respect to an observer) with the passage of time.

Note : Rest and motion are interrelated to each other. An object at rest with respect to one observer may not be at rest with respect to another observer. The same can be said about motion. For a person inside a bus, the fellow passengers are at rest but the same passengers are in motion with respect to a person standing on the ground.
 

Measuring the length of a curved line

Measuring the length of a curved line: We cannot measure the length of a curved line directly by using a metre scale. We can use a thread or divider to measure the length of a curved line.

Measurement Along Curved Line

Is it possible to measure a curved line with a metre scale? Well, it is not so. Hence to measure a curved line the following steps can be taken into account:

• Take a thread and tie a knot at one end.
• From this end measure a small portion of the curved line which is somewhat straight and put the thumb.
• Now again start from the thumb marked position and measure another small portion of the line.
• Repeat this process until you reach the end of the line. Tie a knot on the thread on reaching the end. Now measure the two knots using a metre scale.