DEFINITION QUANTITIES, UNITS AND MEASUREMENT
In daily life, certainly you often hear the terminologies such as length, width, height, time, temperature, and so on. Those terminologies are included into quantities. In physics, quantities are very closely related to measurement.
The definition of quantities, units, and measurement in physics can be expressed as follows.
v Quantities are something that can be measured and expressed in values.
v Units are the standard of comparison in the measurement.
v Measurement is a process of comparing something measured with another as measures made as standard.
FUNDAMENTAL QUANTITIES AND DERIVED QUANTITIES
In physics there are two kinds of physical quantities, those are fundamental quantities and derived quantities. Fundamental quantities are the physical quantities which the units are predetermined, while the derived quantities are the physical quantities which the units are derived from fundamental quantity units.
There are seven fundamental quantities; those are length, mass, time, electric current, temperature, luminous intensity and the amount of substance.
Table 1 Fundamental quantities and their units
| No | Fundamental quantities | Units | Symbol |
| 1 2 3 4 5 6 7 | Length Mass Time Temperature Electric Current Luminous Intensity Amount of Substance | Meter Kilogram Second Kelvin Ampere Candela Mole | m kg s K A Cd mol |
Meanwhile, the derived quantities is other quantities are derived from these fundamental quantities such as volume, density, velocity, force, work and many others.
Table 2 Examples of derived quantities and their units
| No | Derived Quantities | Units | Symbol |
| 1 2 3 4 5 6 | Area Volume Density Velocity Energy Power | Square meter Cubic meter Kilogram/cubic meter Meter/second Joule Watt | m2 m3 kg/m3 m/s J W |
SCALAR QUANTITIES AND VECTOR QUANTITIES
Most of the physical quantities encountered in physics are either scalar or vector quantities. A scalar quantity is defined as a quantity that has magnitude only. Typical examples of scalar quantities are time, speed, temperature, and volume. A scalar quantity or parameter has no directional component, only magnitude. For example, the units for time (minutes, days, hours, etc.) represent an amount of time only and tell nothing of direction. Additional examples of scalar quantities are density, mass, and energy.
A vector quantity is defined as a quantity that has both magnitude and direction. Magnitude of vector is also referred to as the vector's "displacement." It can be thought of as the scalar portion of the vector and is represented by the length of the vector. By definition, a vector has both magnitude and direction. Direction indicates how vector is oriented relative to some reference axis.
Vectors have magnitude and direction, scalars only have magnitude. There are some quantities, like speed, which have very special definitions for scientists. By definition, speed is the scalar magnitude of a velocity vector. A car going down the road has a speed of 50 mph. Its velocity is 50 mph in the northeast direction. Another example is mass and weight. Weight is a force which is a vector and has a magnitude and direction. Mass is a scalar. Weight and mass are related to one another, but they are not the same quantity.
The forces which operate on a flying aircraft, the weight, thrust, and aero dynamic forces, are all vector quantities. The resulting motion of the aircraft in terms of displacement, velocity, and acceleration are also vector quantities. The scalar quantities include most of the thermodynamic state variables involved with the propulsion system, such as the density, pressure, and temperature of the propellants. The energy, work, and entropy associated with the engines are also scalar quantities.
