Science · Class 7 · Chapter 8

Measurement of Time and Motion

Aim: Build a clear, working understanding of this chapter's key ideas, connected to real NCERT examples, worked problems, and everyday situations.
  • Time period — Time for one full oscillation of a pendulum.
  • Oscillatory motion — Motion repeating back and forth.
  • Second (s) — The SI unit of time.
  • Speed — Distance covered per unit time.
  • Average speed — Total distance ÷ total time.
  • Speedometer / Odometer — Measures current speed / total distance.
  • Uniform linear motion — Constant speed, equal distances each equal time.
  • Non-uniform linear motion — Changing speed, unequal distances each equal time.
40 min lesson

Chapter 8 · Concept 1 of 8

Ancient Ways to Measure Time

  • Sundial — Tells time from the position of a shadow.
  • Water clock — Measures time by water flowing out, or a bowl sinking.
  • Hourglass — Measures time by sand flowing between two bulbs.
  • Candle clock — Measures time by how far a candle has burned down.

Chapter 8 · Concept 2 of 8

The Pendulum Clock, and Beyond

  • The 17th-century leap — Christiaan Huygens invented the pendulum clock, inspired by Galileo's studies of swinging pendulums — a major breakthrough in mechanical timekeeping.
  • Modern precision — Quartz clocks use vibrations from a quartz crystal; atomic clocks use vibrations of specific atoms — both are far more precise than any pendulum.

Chapter 8 · Concept 3 of 8

The Simple Pendulum

  • Time period — One oscillation is a full swing: mean → A → mean → B → mean. The time this takes is the time period — it depends only on the pendulum's length, not the bob's mass.

Chapter 8 · Concept 4 of 8

The SI Unit of Time

  • The SI unit of time is the second (s). 60 seconds make a minute; 60 minutes make an hour.
  • Why precision matters — Milliseconds and microseconds matter in sports timing, medical devices like ECGs, music recording, and computing.

Chapter 8 · Concept 5 of 8

Speed

  • Speed tells us how fast or slow something is moving.
  • Speed = Distance ÷ Time — The SI unit of speed is metre/second (m/s); it's also commonly expressed in kilometre/hour (km/h).

Chapter 8 · Concept 6 of 8

Average Speed

  • Why "average"? — Objects rarely move at exactly one speed the whole way — the speed we calculate for a full journey is usually an average.
  • Measuring instruments — A speedometer shows a vehicle's speed; an odometer shows the total distance it has travelled.

Chapter 8 · Concept 7 of 8

Uniform and Non-uniform Linear Motion

  • Uniform linear motion — Constant speed along a straight line — equal distances covered in equal time intervals.
  • Non-uniform linear motion — Changing speed along a straight line — unequal distances covered in equal time intervals.

Chapter 8 · Concept 8 of 8

Is This Motion Uniform?

  • If distance increases by the same amount in every equal time interval, the motion is uniform.
  • Time (s) | 0 | 10 | 20 | 30 | 40
  • Distance (m) — 0 — 8 — 16 — 24 — 32

Quick Recap

Check Your Understanding

  1. 1A car travels 150 metres in 10 seconds. Calculate its speed, and express your answer in km/h.
  2. 2Runner 1 covers 400 m in 50 s. Runner 2 covers the same distance in 45 s. Who is faster, and by how much?
  3. 3A train travels at 25 m/s and covers 360 km. How much time does it take?