Grade 6 Physics Chapter 2

Measurement and Physical Quantities

• Measurement compares an unknown quantity with a known constant or unit.
• Every measurement consists of a numerical value and a unit.
• A physical quantity can be defined as: Physical quantity = Numerical value × unit.
• Standard units ensure uniformity and reliability in measurements, avoiding discrepancies due to human body variations.

Need for Standard Units

• Prior to standard units, measurements were inconsistent.
• Standard units are defined by characteristics that include being of moderate size, unaffected by space and time, unambiguous, non-perishable, and easily reproducible.

Rules for Writing Units

• Unit names are written in lower case, except Celsius and Fahrenheit.
• Symbols for units named after scientists are in upper case, while other symbols remain in lower case.
• Units should not be followed by a full stop and written in plural form only when in words.

Measurement of Length

• Length is the distance between two points; the SI unit is the metre (m).
• A metre is based on a platinum-iridium bar kept in Paris.
• Tools for measuring length include rulers, measuring tapes, vernier calipers, and screw gauges.
• Common units include multiples (kilometre, hectometre) and submultiples (decimetre, centimetre, millimetre).
• Light-year measures astronomical distances, and microscopic measurements use microns and angstroms.

Measuring Techniques

• Accurate measurement requires proper placement and alignment to avoid parallax error.
• For spherical objects, measure diameter using solid blocks and a metre scale.
• Curved lengths can be measured using a thread, while the thickness of small objects can be determined by stacking.

Measurement of Area

• Area represents the surface enclosed by a boundary, measured in square metres (m²).
• Regular and irregular areas are assessed differently, with formulas and graph paper used respectively.

Mass and Weight

• Mass indicates the amount of matter in an object, while weight represents gravitational force acting on it.
• SI unit of mass is kilogram (kg); subunits include gram and milligram.
• Balance scales (grocer’s, beam, physical, electronic) are used to measure mass accurately.

Measurement of Time

• Time represents the interval between events; the SI unit is the second (s).
• Historical methods included sundials; modern timekeeping uses atomic clocks.
• Devices include clocks, watches, and stopwatches for various measurements.

Measurement of Temperature

• Temperature indicates the degree of hotness or coldness, measured with thermometers.
• SI unit is Kelvin; common scales are Celsius and Fahrenheit.
• Laboratory thermometers measure up to -100°C to 110°C, while clinical thermometers measure human body temperature.

Approximation in Measurement

• Approximation provides a quick but not exact measurement; accuracy reflects closeness to the true value.
• Errors can be mitigated by averaging multiple observations.

Standard Weights and Measures

• The Department of Weights and Measures in India ensures correctness of weights and measuring devices.
• Characteristics of accurate measuring devices include verification stamps and correct functionalities.

Explore the foundations of measurement in physics with this quiz on physical quantities. Understand how measurement involves comparing unknown quantities with known units and discover the significance of standard units. Test your knowledge on numerical values and units in this essential chapter.