Overview
This lecture covers the importance and methods of measuring physical quantities, including key SI units, measurement instruments, and techniques to ensure accuracy.
Importance of Measurement
- Measurement standardizes evaluation and comparison of quantities using agreed units.
- Accurate measurements lead to greater precision in fields like engineering, medicine, and manufacturing.
- Measurements help quantify and understand complex phenomena such as weather.
- Measurement allows monitoring of progress and changes over time, for example in construction projects.
The International System of Units (SI)
- Measurement of physical quantities requires defined units.
- The SI system (Système International d’Unités) is the modern metric standard.
- Seven SI base units: length (meter), mass (kilogram), time (second), electric current (ampere), temperature (kelvin), luminous intensity (candela), amount of substance (mole).
Common SI Units and Measurement Instruments
- Length: meter (m), measured with meter ruler, tape measure, or calliper.
- Mass: kilogram (kg), measured with a balance.
- Time: second (s), measured with a stopwatch or clock.
- Temperature: kelvin (K), measured with a thermometer.
Multiples, Submultiples, and Derived Units
- SI units use prefixes for multiples/submultiples (1 km = 1000 m, 1 cm = 0.01 m).
- Area: measured in square centimeters (cm²).
- Volume: measured in cubic centimeters (cm³).
Measuring Techniques and Error Prevention
- To avoid parallax error, read measuring scales at eye level.
- Rulers use different units for flexibility and context.
- Callipers measure thickness or diameter, especially for curved objects.
Measuring Volume
- Volume is the space matter occupies, measured for liquids and solids.
- Liquids form a meniscus; always read the meniscus at eye level.
- Volume of regular objects: calculate using length × width × height.
- Volume of irregular objects: measure liquid displacement in a container.
Measuring Mass, Time, and Temperature
- Mass is the amount of matter, measured in grams or kilograms with a balanced instrument.
- Zero the balance before measuring mass.
- Time is the interval of events, measured in seconds with a clock or stopwatch.
- Temperature reflects heat, measured using thermometers in Celsius, Fahrenheit, or Kelvin.
- Avoid parallax error when reading thermometers.
Key Terms & Definitions
- Parallax Error — Inaccurate measurements from viewing a scale at an angle instead of directly at eye level.
- Meniscus — The curved surface of a liquid in a container.
- SI Units — The international standard units for measuring physical quantities.
- Calliper — A tool for measuring the thickness or diameter of objects.
- Balance — An instrument for measuring mass.
Action Items / Next Steps
- Practice measuring textbook length, volumes with cylinders, and mass using a balance.
- Review SI base units and corresponding instruments.
- Prepare to avoid parallax error in future experiments.