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Understanding Physical Quantities and Units

Jun 3, 2025

Physical Quantities and Units

Introduction

  • Presented by Timothy from Cognito Academy
  • Focus on measurements, specifically physical quantities and units.

Physical Quantity

  • Definition: A measurable quantity of an object (e.g., mass).
  • Representation: Magnitude and Unit (e.g., 10 kg, where 10 is the magnitude and kg is the unit).

Types of Physical Quantities

  1. Base Quantities

    • Fundamental physical quantities not defined by other quantities.
    • Seven types, five essential base quantities:
      • Length (SI Unit: Meter)
      • Mass (SI Unit: Kilogram)
      • Time (SI Unit: Second)
      • Temperature (SI Unit: Kelvin)
      • Current (SI Unit: Ampere)

  2. Derived Quantities

    • Formed by combining base quantities.
    • Examples:
      • Volume = Length × Breadth × Height
      • Speed = Distance / Time

Standard Form and Prefixes

  • Large/small quantities can be expressed in standard form for simplification.
  • Example: 0.0001 seconds can be written as 10^-4 seconds = microsecond.
  • Common Prefixes:
    • Nano (10^-9)
    • Micro (10^-6)
    • Milli (10^-3)
    • Centi (10^-2)
    • Deci (10^-1)
    • Kilo (10^3)
    • Mega (10^6)
    • Giga (10^9)

Precision in Measurements

  • Precision: The smallest unit an instrument can measure.
  • Example Instruments:
    • Ruler: Measures up to 1 mm.
    • Vernier Caliper: Measures up to 0.1 mm, suitable for 1 to 15 cm lengths.
    • Micrometer Screw Gauge: Measures up to 0.01 mm, best for lengths below 2.5 cm.
    • Stopwatch: Typical precision up to 0.001 seconds, but readings taken to 1 decimal place (e.g., 30.9 seconds).

Reducing Experimental Error

  • Random Error: Affects readings due to human factors (e.g., reaction time).
  • Pendulum Example:
    • Period: Time for one complete cycle.
    • To find the period: Measure time for 20 cycles and divide by 20 to reduce inaccuracy.
  • Take multiple readings for accuracy.

Common Errors in Measurement

  • Parallax Error: Occurs from misalignment of the eye with the measurement scale.
    • To avoid: Align eye with the marking directly.

Conclusion

  • End of video on measurements.
  • Encouragement to like, subscribe, and turn on notifications for more content.

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