Length is one of the fundamental physical quantities. A ruler is used to measure the length of an object. It is also used to measure the length of a straight line. A non-stretchable string or thread is used to measure the length of a curved line.

Procedure to Measure the Length of an Object (or) a Straight Line

• First place the ruler along the edge of the object whose length is to be measured, with the zero mark of the ruler placed at one end of the object.
• On the ruler, note the reading at the other end of the object.
• This gives the measure of the length of the object.
• The same procedure can be followed to measure the length of a straight line.

Procedure to Measure the Length of a Straight Line Using a Damaged Ruler

• Place the broken or damaged ruler along the edge of the object whose length is to be measured in such a way that any visible mark coincides with one end of the object.
• Now note the reading on the ruler at the other end of the object.
• The difference between the two readings gives the length of the object.

Procedure to Measure the Length of a Curved Line

• Take a non-stretchable string or a thread and tie a knot at one of its ends.
•  Place the knotted end of the thread at one end of the curved line.
•  Holding the thread steadily with your fingers, stretch it along the curved line until you reach the other end.
•  Now make a mark on the thread where it reaches the other end.
•  Finally, place the thread along a metre scale and measure the length between the knot and the marked point.
•  This gives the length of the curved line.

When noting the reading on a ruler, you should look at it with the eyes directly above the reading, and not in an oblique way. Otherwise, you will not be able to note the reading accurately. If the zero mark of the ruler does not coincide with the first end of the object, then the difference between the readings at the two ends gives the length of the object.