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UNIT 1: MEASUREMENT OF QUANTITIES

  • Physical quantities are either scalars or vectors.

    • Scalars don’t have a direction.

    • Vectors have a direction.

  • SI units

    • SI base units include:

      • m

      • kg

      • s

      • A

      • K

    • Derived units are based on base units, for example:

      • m/s

      • m/s2

      • N (which really means kgm/s2)

  • Prefixes can be used if a unit is too big or too small for a purpose.

    • mega (M) means 1,000,000

    • kilo (k) means 1,000

    • deci (d) means 1 / 10

    • centi (c) means 1 / 100

    • milli (m) means 1 / 1,000

    • micro (µ) means1 / 1,000,000

  • Length measuring instruments

    • Ruler or measuring tape has an accuracy of ±1mm.

    • Vernier calipers has an accuracy of ±0.1mm.

    • Micrometer screwguage has an accuracy of ±0.01mm.

    • To measure length using vernier calipers or micrometer screwguage:

Length = Main scale reading + Minor scale reading x Accuracy

  • Time measuring instruments

    • Stopwatch has an accuracy of ±0.01s

    • Ticker-tape timer has an accuracy of ± (1 / 50) of a second or ± (1 / 60) of a second.

    • Pendulum clock

  • Pendulum

    • Oscillation is a vibration.

    • Time-period is the time taken for one oscillation.

    • Amplitude is the maximum displacement from central position.

    • A pendulum of a particular length has a constant time-period. It is not affected by amplitude.

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