This chapter explains the importance of measurement in finding the size, length, or amount of objects using standard units. In earlier times, people used non-standard units such as hand span, footstep, and cubit, which were not accurate or reliable. To ensure uniformity, the metre (m) was introduced as the standard unit of length, with centimetre (cm) and millimetre (mm) as smaller units and kilometre (km) as a larger unit. The chapter describes different measuring instruments like rulers, measuring tapes, and metre rods, and stresses the need for correct measurement techniques to avoid parallax error. It also introduces the concept of motion, defined as a change in position with time, and explains various types of motion such as rectilinear, circular, periodic, and rotational motion. The chapter concludes by stating that rest and motion are relative, as the same object may appear at rest or in motion depending on the observer.
Key Points
Measurement means finding the size, length, or amount of something using standard units.
Earlier, people used non-standard units (hand span, footstep, cubit), but they were not reliable.
Standard unit of length = metre (m). Smaller units = centimetre (cm), millimetre (mm). Larger unit = kilometre (km).
Instruments for measuring length: ruler/scale, measuring tape, metre rod, vernier caliper (higher classes).
To measure correctly, keep the scale straight and eye at level with the marking to avoid parallax error.
Motion means change in position of an object with time.
Types of motion:
– Rectilinear motion – Straight line motion (train on track).
– Circular motion – Around a circle (hands of a clock).
– Periodic motion – Repeats after equal intervals (pendulum).
– Rotational motion – Spinning around an axis (top, Earth).
Rest and motion are relative – the same object may appear at rest to one observer but in motion to another.
👉 👉Accurate measurement and understanding of motion are essential in science and daily life. Using standard units helps us compare and share results reliably.