NCERT Curiosity · Class 7 · Science
Measurement of Time and Motion
A school stopwatch, and Olympic ultra-precise timing — people measured time long before clocks existed at all.
Timekeeping The Pendulum Speed Uniform Motion
Key idea
Ancient Ways to Measure Time

Sundial

Tells time from the position of a shadow.

Water clock

Time from water flowing out, or a bowl sinking.

Hourglass

Time from sand flowing between two bulbs.

Candle clock

Time from how far a candle has burned down.

Key idea
The Pendulum Clock, and Beyond
The 17th-century leap

Christiaan Huygens invented the pendulum clock, inspired by Galileo's studies of swinging pendulums.

Modern precision

Quartz clocks use crystal vibrations; atomic clocks use atom vibrations — both far more precise.

Key idea
A pendulum's time period depends only on its length, not the bob's mass.
One oscillation is a full swing: mean → A → mean → B → mean. The time this takes is the time period.
Key idea
60 × 60
Seconds in an hour — the second (s) is the SI unit of time. Milliseconds and microseconds matter in sports timing, ECGs, and computing.
Key idea
Speed = Distance ÷ Time
Speed tells us how fast or slow something is moving. Its SI unit is metre/second (m/s), also expressed as km/h.
Key idea
Average Speed
Objects rarely move at exactly one speed the whole way — the speed we calculate is usually an average.

Speedometer

Shows a vehicle's current speed.

Odometer

Shows the total distance travelled.

Key idea
Uniform and Non-uniform Motion
Uniform

Constant speed — equal distances covered in equal time intervals.

Non-uniform

Changing speed — unequal distances covered in equal time intervals.

Chapter · key terms to remember
Key Terms

Time period

Time for one full oscillation of a pendulum.

Oscillatory motion

Motion repeating back and forth.

Second (s)

The SI unit of time.

Chapter · key terms to remember
More Key Terms

Speed

Distance covered per unit time.

Average speed

Total distance ÷ total time.

Speedometer / Odometer

Measures current speed / total distance.

Chapter · key terms to remember
More Key Terms

Uniform linear motion

Constant speed, equal distances each equal time.

Non-uniform linear motion

Changing speed, unequal distances each equal time.

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