๐ฌ Chapter 8 โ Measurement of Time and Motion
Class 7 Science | Curiosity | EduGrown Notes
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โฑ๏ธ Measurement of Time and Motion โ from sundials to GPS!
โฐ Measurement of Time โ Ancient to Modern
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โ๏ธEarliest time measurement: rising/setting of Sun, Moon phases, changing seasons
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First, calendars were made โ then devices to measure time within a day
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โณ Sundial โ measures time using shadow of the Sun!
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๐ Water clock โ measures time by flow of water
โ๏ธ Sundial
โUses the shadow of an object cast by sunlight to tell time
๐๏ธSamrat Yantra at Jantar Mantar, Jaipur = world's largest sundial (27 m tall!) โ UNESCO site
๐ง Water Clock
โWater flows in/out of a vessel at a steady rate โ markings show passage of time
โAncient India: Ghatika-yantra (sinking bowl type) used at monasteries & palaces
โณ Hourglass
โSand flows from one glass bulb to another at a steady rate
๐ฏ๏ธ Candle Clock
โCandle with markings โ as wax burns down, time is measured
๐ฐ๏ธ The Pendulum Clock
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๐ฐ๏ธPendulum clock invented in 1656โ1657 by Christiaan Huygens โ inspired by Galileo's observations
๐ญGalileo Galilei discovered: a pendulum of a given length always takes the same time for each swing!
โฑ๏ธTime period = time for ONE complete oscillation (to and fro swing) of a pendulum
๐A longer pendulum โ more time per swing | Shorter pendulum โ less time per swing
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๐ฐ๏ธ Simple pendulum โ bob suspended by thread, swings back and forth!
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โฑ๏ธ Modern clocks measure time in seconds!
๐ Motion & Speed
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๐Motion = change in position of an object with respect to its surroundings over time
๐Distance = total path length covered by an object
โกSpeed = Distance รท Time | Speed = Distance / Time
๐Unit of speed: m/s (metres per second) or km/h (kilometres per hour)
๐ Types of Motion
โก๏ธUniform motion: equal distance in equal time intervals (constant speed)
๐Non-uniform motion: unequal distances in equal time intervals (changing speed)
๐ Measuring Motion
๐Distance measured with: ruler, measuring tape, odometer
โฑ๏ธTime measured with: stopwatch, wristwatch, clock
๐Speed calculated: Speed = Distance รท Time
๐ก Speed Calculations!
๐ If Prerna runs 100m in 12 seconds: Speed = 100 รท 12 = 8.33 m/s
๐ A car travels 120 km in 2 hours: Speed = 120 รท 2 = 60 km/h
Formula: Speed = Distance / Time | Distance = Speed ร Time | Time = Distance / Speed
๐ A car travels 120 km in 2 hours: Speed = 120 รท 2 = 60 km/h
Formula: Speed = Distance / Time | Distance = Speed ร Time | Time = Distance / Speed
โญ Quick Summary
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๐ Key Points
โฐAncient clocks: Sundial (shadow), Water clock (Ghatika-yantra), Hourglass, Candle clock
๐ฐ๏ธPendulum clock (1656, Huygens) โ pendulum of same length has same time period!
๐Speed = Distance / Time | Units: m/s or km/h
๐Uniform motion = constant speed | Non-uniform = changing speed