Need for Measurement: Units

Standard Units of Measurement

A standard unit of measurement is a way of putting a common language to a quantifiable quantity.  It is through units that we can understand the relationship between objects and measurements. Measurements are essential for understanding quantities, so it is important to understand how they work and what kinds of units exist.

Need for Measurement

The same idea can be said in different ways when changing languages. Similarly, units allow quantities to be expressed in different languages. In the world, there are different systems and units to measure magnitudes such as length, area, mass, volume, etc. For example, concerning area, we can express the quantity in acres or square metres. In this case, about 4,046 square metres equals one acre. Hence, there is a way to define measurements: a unit and a specific quantity. Units also apply to temperature. Within the thermometer, there are different ways of measuring the length of the mercury rod. For each type of magnitude, it is necessary to determine a unit and quantity to give greater precision.

History of Unit Systems

The first systems arose in the 18th century in France and were born out of the need to be able to count elements. The systems of measurements were born and continue to be used, as they allow the consolidation of quantities by making use of certain rules, the same information can be interpreted anywhere on the planet. Multiple systems of units can be found such as the technical, decimal, natural, Anglo-Saxon and CGS systems, however, almost all these systems are derived from the same units of measurement of the international and English systems.

The Seven Base Units of Measurement

There are seven types of basic units, with which any type of measurement can be expressed. These measurements can be transformed to express any kind of physical quantity.

Property	Unit	Symbol
Length	meter	m
Mass	kilogram	kg
Time	second	s
Electric current	ampere	A
Temperature	kelvin	K
Amount of Substance	mol	mol
Luminous intensity	candela	cd

Derived Units

In addition to the seven units mentioned above, other units are derivatives of the base units.  Some common examples are velocity, acceleration, work, energy and more.  Some more examples are listed below: Frequency – Hertz (Hz); 1 Hz = s^-1 Power – Watt (W); 1 W = 1kgm²s^-3 These units are called derived because their value is determined from another base unit. In the table below there are the different derived magnitudes and the units in the SI.

Quantity with Symbol	Unit (S.I.)	Symbol
Velocity (v)	Metre per sec	ms–1
Area (A)	Square metre	m2
Volume (V)	Cubic metre	m3
Density (r)	Kilogram m-3	Kg m–3
Energy (E)	Joule (J)	Kg m2s2
Force (F)	Newton (N)	Kg ms-2
Frequency (n)	Hertz	Cycle per sec
Pressure (P)	Pascal (Pa)	Nm-2
Electrical charge	Coulomb (C)	A-s (ampere – second)

Methods for Measuring Length

Various tools and methods can be used to measure lengths and distances, objects, places, and distances. Some ways of measuring are listed below:

1. -Small lengths: thanks to tapes, rulers and scales can be measured properly. For example, the length of a pencil.
2.  Very small distances: vernier callipers or adjusting screws are used for this purpose. For example, the thickness of a piece of cardboard.
3. Very large distances: the parallax method is used. This method is used to measure distances to celestial objects, e.g., the distance to the moon.

Methods for Measuring Curved Line

The distance between two points on a straight line requires tools other than a ruler. A simple way to make this measurement is to use a string to measure an arc, mark the length of the measurement and then measure this length using a ruler. This gives the length of the curved line AB.

Measurement of Volume

Depending on whether the object has a regular shape or not, different approximations can be used. In the case of a regular shape, the volume can be measured using two techniques:

1. Measuring the length of the sides using a calliper or tape.

For example, a calliper can be used to measure the length and radius of a cylinder. The volume will then be the multiplication of these such that: V=πr²l

2. If the object is not regular or you do not have rulers, one way to measure this is to immerse the object in liquid and observe the volume displaced.

For example, if in a cubic shaped tub, you observe an increase in height when immersing an object of dl the volume can be found such that: V=dll2l3