Chapter 8: Measurement of Time and Motion
From sundials and the Ghatika-yantra to pendulums and atomic clocks, people have always found clever ways to measure time. In this chapter we time a pendulum, learn the second and how to write units, calculate speed, distance and time, convert between m/s and km/h, and tell uniform motion from non-uniform motion.
In this chapter you will
- describe how time was measured in the past and present
- find the time period of a pendulum
- calculate speed, distance and time, and convert units
- tell uniform from non-uniform motion
Topics
- Measurement of Time NCERT 8.1
Early clocks used shadows, water, sand and candles; the Ghatika-yantra measured ghatis of 24 minutes.
- Slow or Fast: Speed NCERT 8.2–8.3
Speed = distance ÷ time; units m/s or km/h (× 5/18 to change km/h to m/s).
- Uniform and Non-uniform Motion NCERT 8.4
Uniform linear motion: equal distances in equal times along a straight line.
Key words
- Oscillation
- one complete to-and-fro swing
- Time period
- time for one oscillation
- Second (s)
- the SI unit of time
- Speed
- distance covered per unit time
- Uniform motion
- equal distances in equal times in a straight line
- Non-uniform motion
- unequal distances in equal times
- Ghatika-yantra
- an ancient Indian sinking-bowl water clock
Summary
- Clocks rely on processes that repeat at equal intervals: shadows, water, pendulums, quartz, atoms.
- A pendulum's time period depends on its length, not its bob; SI unit of time: second (s).
- Speed = distance ÷ time (m/s or km/h); distance = speed × time.
- Uniform motion covers equal distances in equal times; most real motion is non-uniform.