Time measurement is imp in our daily life and sports. From school races to catching a bus, we rely on clocks and watches. Modern devices like stopwatches, mobile phones, and wall clocks give us accurate time. Even visually impaired people use Braille or talking watches. But how did people measure time in ancient days? Let’s study how timekeeping evolved from simple tools to high-tech gadgets.
Ancient Time-Measuring Devices
Long ago, people used clever but simple tools to track time:
- Sundials: Used shadows cast by the Sun. The shadow’s position changed as the Sun moved across the sky.
- Water clocks: Measured time by water flow. Two types:
- Water dripped out of a marked vessel.
- A bowl with a hole sank in water, showing time.
- Hourglasses: Sand flowed from one glass bulb to another in a fixed time.
- Candle clocks: Burned candles had marks to show time as the wax melted.
Fun Fact: The Samrat Yantra in Jaipur is a huge sundial that can measure time as short as 2 seconds!
Ancient Indian Devices:
- Ghatika-yantra: A sinking bowl water clock.
- Time was measured in ghatis (1 ghati = 24 minutes).
- A day was divided into 60 ghatis.
These devices were less accurate than today’s clocks but were imp for daily life.
Evolution of Timekeeping
Timekeeping improved over centuries:
- Ancient India: Used shadows and water clocks.
- Kautilya’s Arthasastra talked about shadow-based time.
- Varahamihira gave exact calculations for shadows.
- Mechanical clocks: Later, clocks with gears and weights were made.
- Pendulum clock: A big leap in accuracy.
- Invented by Christiaan Huygens in 1656.
- Galileo’s studies on pendulums inspired this.
- Modern clocks:
- Quartz clocks: Use vibrations of quartz crystals.
- Atomic clocks: Super precise, lose only 1 second in millions of years!
Scientists keep working to make clocks even more accurate.
A Simple Pendulum
A pendulum is a bob tied to a string, hanging from a fixed support. When you pull and release it, it swings back and forth.
- Oscillatory motion: The swinging motion is called this.
- Time period: Time taken for one full swing (left to right and back).
- Depends on the pendulum’s length. Longer string = longer time period.
- Mass of the bob doesn’t affect the time period.
- Uses: Pendulums are used in clocks for accurate timekeeping.
SI Unit of Time
The standard unit of time is the second (s).
- Larger units:
- 60 seconds = 1 minute (min).
- 60 minutes = 1 hour (h).
- Rules for writing units:
- Use lowercase letters (e.g., ‘s’, ‘min’, ‘h’).
- No full stop after symbols.
- Leave a space between number and unit (e.g., 10 s).
- Avoid writing ‘sec’ or ‘hrs’—it’s incorrect!
Importance of Precise Timekeeping
Accurate time is imp in many fields:
- Sports: Races are timed to milliseconds.
- Medicine: ECG machines track heartbeat timing.
- Music: Recordings capture sound thousands of times per second.
- Technology: Smartphones and computers need microsecond precision.
- Space: Satellites and rockets rely on exact time measurements.
Better clocks mean better tech and easier life!
Slow or Fast
How do we know if something is moving fast or slow?
- Faster objects cover more distance in the same time.
- Example: In a race, the runner ahead is faster.
- Speed tells us how fast an object moves.
Relationship between Speed, Distance, and Time
Speed = Distance covered per unit time.
Formula:
Units:
- SI unit: metre per second (m/s).
- Common unit: kilometre per hour (km/h).
- Average speed: Used when speed changes during motion.
Uniform and Non-uniform Linear Motion
- Linear motion: Movement in a straight line (e.g., train on a straight track).
- Uniform motion: Constant speed. Equal distances in equal times.
- Rare in real life.
- Non-uniform motion: Speed changes. Unequal distances in equal times.
- Common in daily life (e.g., cars in traffic).
Questions and Answers
- Calculate the speed of a car that travels 150 metres in 10 seconds. Express in km/h.
- Speed = 150 m / 10 s = 15 m/s.
- Convert: 15 m/s × 3.6 = 54 km/h.
- Answer: 54 km/h.
- A runner completes 400 m in 50 s. Another does it in 45 s. Who is faster and by how much?
- Runner 1: 8 m/s. Runner 2: ≈8.89 m/s.
- Answer: Second runner is faster by 0.89 m/s.
- A train covers 360 km at 25 m/s. How much time does it take?
- Time = 360,000 m / 25 m/s = 14,400 s = 4 h.
- Answer: 4 hours.
- A train travels 180 km in 3 h. Find its speed in km/h and m/s. What distance will it cover in 4 h?
- (i) 60 km/h. (ii) 16.67 m/s. (iii) 240 km.
- Compare a horse (18 m/s) and a train (72 km/h).
- Train: 20 m/s. Horse: 18 m/s.
- Answer: Train is faster by 2 m/s.
- Difference between uniform and non-uniform motion?
- Answer: Highway car (uniform), city car (non-uniform).
- Fill the table for uniform motion (distance increases by 8 m every 10 s).
- Answer: 20 s = 16 m, 60 s = 48 m.
- Is a car’s motion uniform if it covers 60 km, 70 km, 50 km in 3 hours?
- Answer: Non-uniform. Avg speed = 60 km/h.
- Which motion is common—uniform or non-uniform? Give examples.
- Answer: Non-uniform (cycling, bus, walking).
- Is the object’s motion uniform? Find avg speed.
- Answer: Non-uniform. Avg speed = 0.6 m/s.
- A vehicle covers 2 km in 200 s. Find speed for last 1 km and avg speed.
- Answer: 20 m/s for last part. Avg speed = 10 m/s.
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