### Fisika Bilingual Besaran dan Satuan Kelas 7

• 1. Physical Quantities, Units, and Measurement Physics is an empirical study. Everything we know about the physical world and about the principles that govern its behavior has been learned through observations of the phenomena of nature. The ultimate test of any physical theory is its agreement with observation and measurements of physical phenomena. Physics is inherently a science of measurement. Physical Quantities is any number or set of number used for a quantitative description of a physical phenomenon. All physical quantities consist of a numerical magnitude and a unit. For example, the measurement result of the length of a copper stick is 100 cm. 100 represents the numerical magnitude and cm represents the unit. I. Physical Quantities and Units A. Base Quantities, Base Units and Derived Units In all of physics there are only seven base quantities, each quantity has a unit, corresponding to the quantities. These seven base quantities are presented in Table I-1 below. Table I-1. Seven Base Quantities Quantity Unit Symbol Dimension Length meter m L Mass kilogram kg M Time second s T Electric Current ampere A I Thermodynamic temperature kelvin K  Amount of substance mole mol N Luminous intensity candela cd J In measuring a quantity, we always compare it with some established reference standard: 1. The standard of Mass is the mass of cylinder of platinum-iridium alloy, designated as one kilogram. 2. The standard of length is a meter bar of platinum- iridium alloy 3. The standard of time is the time required for 9,192,631,770 cycles of this radiation (1 Second) 4. Amount of substance in mole represents the amount containing a number of particles equal to the Avogadro constant (NA = 6,02 x 1023 molecules/mol). Historically, the reverse process was one used to obtain NA: that is, from the measured mass of the hydrogen atom. Example I-1 Use the Avogadro constant to determine the mass of a hydrogen atom Solution: One mole of hydrogen (atomic mass = 1.008 u) has a mass of 1.008 x 10-3 kg and contains 6.02 x 1023 atoms. Thus one atom has a mass kg kg 3  1.008  10  m 27 23 1.67 10 6.02 10     Most of physics quantities have the units as a combination of base units. Such units are called Derived units. Table 2 shows some derived units in mechanics.
• 2. Table I-2. Basic Mechanical Units Quantities SI Units (MKS) CGS US Common Dimension Length meter (m) Centimeter (cm) Foot (ft) L Time second (s) second (s) Second (s) T Mass kilogram (kg) gram (gr) slug M Velocity m/s cm/s ft/s L/T Acceleration m/s2 cm/s2 ft/s2 L/T2 Force kg m/s2 = Newton (N) gr m/s2 = dyne slug ft/s2 = pound (lb) M L/T2 Work N m = joule (j) dyne cm = erg lbft = ftlb M L2/T2 Energy joule erg ftlb M L2/T2 Power j/s = watt erg/s ftlb/s M L2/T3 A.1. Unit Consistency and Conversion An equation must always be dimensionally consistent; this means that two terms may be added or equated only if they have the same units. Example I-2 1. 2 m + 20 cm = 2 m + 0,2 m = 2,2 m 2. Distance = velocity x time = (m/s) x s = m The algebraic properties of units provide a convenient procedure for converting a quantity from one unit to another. Equality is sometimes used to represent the same physical quantity expressed in two different units. Example I-3 1. 1 min = 60 s does not mean that the number 1 is equal to the number 60, but rather that 1 min represents the same physical time interval as 60 s. and then divide by 60 s, or multiply by quantity (1 min/60s), without changing the physical meaning. To find the number of seconds in 3 min, we write: 3 min = (3 min)(60s/1 min) = 180 s. 2. Similarly, converting 50 km/h (kilometer per hour) in to meter per second 50 km/h = (50 km / h)(1000m/km)(I h/3600 s) = 13.89 m/s A.2. Scientific Notation In calculation with very large or very small numbers, we encounter the difficulty because we have to write a series of number. To overcome this difficulty one use the scientific notation, i.e.the scientifically methode to write the number. Table of the scientific notation is given in Table I-3 below. Table I-3. The Scientific Notation Number Powers of ten Prefix Symbol 0.000 000 000 000 000 001 10-18 exa E 0.000 000 000 000 001 10-15 femto f 0.000 000 000 001 10-12 pico p 0.000 000 001 10-9 nano n 0.000 001 10-6 mikro  0.001 10-3 mili m 0.01 10-2 centi c 0.1 10-1 deci d 10 101 deka da 100 102 hecto H 1000 103 kilo K 1,000,000 106 mega M 1,000,000,000 109 giga G 1,000,000,000,000 1012 tera T 1,000,000,000,000,000 1015 peta P 1,000,000,000,000,000 000 1018 atto A