Measurement of Time and Motion

About this chapter

Measurement of Time and Motion is the eighth chapter of Class 7 Curiosity. Through Prerna the sprinter and her amazement at how Olympic timing has improved, the chapter builds five core ideas. First, ancient ways to measure time — sundials, water clocks (Ghatika-yantra mentioned by Aryabhata), hourglasses, candle clocks — and India's heritage in this area, including the Samrat Yantra at Jantar Mantar, Jaipur, where the shadow moves about 1 mm per second. Second, the simple pendulum: a small metallic bob suspended by a thread shows oscillatory, periodic motion between two extreme positions about a mean position. One oscillation is mean to extreme to other extreme and back. The time taken for one oscillation is the time period, found in Activity 8.2 to depend on the pendulum's length but not on the bob's mass — Galileo's discovery in church. Third, the SI unit of time is the second (s); 60 s = 1 min, 60 min = 1 h, with strict writing rules (no full stop, no plural 's', single space between number and unit). Fourth, speed compares distances covered in unit time; SI unit is metre/second (m/s), also expressed as km/h; speed = total distance / total time, with companion formulas distance = speed x time and time = distance / speed; what we calculate is average speed. Fifth, uniform linear motion (constant speed along a straight line — equal distances in equal intervals) versus non-uniform linear motion (changing speed — unequal distances in equal intervals), illustrated by Trains X and Y in Table 8.3. CTET Paper 2 Science tests this chapter through pendulum-property reasoning (length vs mass), unit-of-time conventions, speed/distance/time calculations, uniform-vs-non-uniform identification, and pedagogy of Activities 8.1-8.4. The four tests below — Practice 15, Quiz 15, Hard 15, Mastery 30 — cover these ideas at exam depth.