Chapter 1: Physical Quantities, Units and Measurements

PHYSICS Physical Quantities, Units and Measurements What Are Physical Quantities? All objects can be described by their physical quantities . A physical quantity is a quantity that can be measured . It typically consists of a numeral magnitude and a unit . E.g. 0.16 m. There are 7 basic physical quantities , or base quantities . We use a system of standardised units called SI units . Base quantities and their SI units Base Quantity SI Unit and Symbol Length Metre, m Mass Kilogram, kg Time Second, s Electric current Ampere, A (Thermodynamic) temperature Kelvin, K Amount of substance Mole, mol For physical quantities with very big or very small magnitudes, we can write them in the standard form with the format: A × 10 n , where 1 ≤ A < 10, where n is an integer. NOTE: The number of s.f. in the standard form varies in questions! Example of standard forms Example of Physical Quantity Magnitude and Unit Standard Form MADE BY 로켓 백만

PHYSICS Length of the F1 Singapore Grand Prix Circuit (hehe sanjay) 30 900 m 3.09 × 10 5 m Speed of light in vacuum 300 000 000 m/s 3.0 × 10 8 m/s Diameter of a hydrogen atom 0.000 000 000 05 m 5.0 × 10 -11 m We can also use common prefixes to represent submultiples (smaller than 10) and multiples (bigger than 10) of 10 of the SI units. Some common prefixes and their symbols Factor Prefix Symbol Multiples 10 12 10 9 10 6 10 3 tera- giga- mega- kilo- T G M k Submultiples 10 -1 10 -2 10 -3 10 -6 10 -9 deci- centi- milli- micro- nano- d c m µ n MADE BY 로켓 백만

PHYSICS How Do We Measure Physical Quantities? The objects in our physical world are in a range of sizes as indicated by their orders of magnitude . - *Size of a typical atom = 1 × 10 -10 m. Its order of magnitude is -10 . - *Size of Earth = 6.378 × 10 6 m. Its order of magnitude is 6 . We can measure the physical quantity of length using various measuring instruments . - The measuring tape is commonly used to measure objects up to one metre . - The metre rule is commonly used to measure objects that are up to several centimetres to one metre . - The digital calipers (i.e. Vernier calipers) are a useful instrument to measure objects’ internal and external diameters and depths that are up to 15 cm . - The digital micrometer screw gauge is used to measure objects that are up to 2.5 cm . We choose the most suitable measuring instrument based on its precision and range . - Precision is