Class 6 Science Chapter 5 Measurement of Length and Motion Revision Notes

Getting a length measurement right in Chapter 5 depends on avoiding parallax error and picking the correct starting point on the scale — the key units and techniques are gathered below.

Last Updated: September 23, 2026

Units of Length

• SI unit of length: metre (m).
• 1 km = 1000 m; 1 m = 100 cm; 1 cm = 10 mm; 1 km = 1,00,000 cm.
• Body-part units (handspan, arm length, foot length) vary person to person — replaced by fixed standard units.

Correct Measuring Technique

• Place the scale in direct contact with the object.
• If the zero mark is broken, measure from another clear mark and subtract.
• Parallax error: avoid by keeping the eye directly above the reading point.
• Curved lines: use a flexible thread, then straighten and measure against a rigid scale.

Position and Motion

• Reference point: a fixed point used to judge if position is changing.
• Motion: position changes with time relative to a reference point. Rest: it does not.

Types of Motion (3 types taught in this chapter)

Note: “Rotational motion” is not a separate category at this level — spinning objects are grouped under circular motion.

Quick revision: Solutions | Extra Questions for this chapter.

Frequently Asked Questions

Why is a standard unit of measurement necessary when measuring length?
A standard unit ensures measurements taken by different people in different places give the same, comparable result, avoiding confusion from everyone using their own arbitrary reference.

What is the difference between a simple estimate of distance and an accurate measurement using an instrument?
An estimate is an approximate guess based on visual judgment, while an accurate measurement uses a proper instrument, such as a metre scale, to obtain a precise and reliable value.

Written by Satish

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