Measuring Length Correctly, Even Curved Lines

Class 6 Science · Chapter 5: Measurement of Length and Motion · NCERT Curiosity section 5.3–5.4

Learn

Sahil's ruler has a broken end: it starts at 1 cm. Can he still measure? Yes! He puts one end of the pencil at the 1 cm mark and reads 8.5 cm at the other end. The length is 8.5 − 1 = 7.5 cm.

length = end reading − start reading

Tips for correct measuring: place the ruler along the object, touching it. Start at zero, or at any full mark and subtract. Keep your eye directly above the mark: looking from the side gives a wrong reading.

How do you measure a curved line, like a road on a map or the edge of a leaf? Lay a thread carefully along the curve, mark where it ends, straighten the thread and measure it with a ruler. For a thick round object like a bottle, wrap a thread or a measuring tape around it.

Explore: measure with a broken ruler.

1. This ruler starts at 2 cm. Tap both ends of the crayon.
2. Now measure the key.

Remember

• Length = reading at the end − reading at the start. A broken ruler still works.
• Keep the eye straight above the mark; use a thread for curved lines.

Quick check

A crayon lies from the 3 cm mark to the 9 cm mark of a ruler. How long is it?

1. 6 cm
2. 9 cm
3. 12 cm
4. 3 cm

Think about it

Plan how you would measure the distance around your wrist with only a strip of paper and a ruler.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.