Quantities and Units – Definition, Grouping and Examples

Quantities and Units – Definition, Constants and Examples in Life – Without us realizing it, every day we use measuring tools as a tool to simplify our work and to simplify our activities. The measuring tools used in everyday life that we often encounter are measuring instruments of basic quantities. Various kinds of measuring instruments of basic quantities are what make it easier for us to know how many measurements are obtained.

However, what we often encounter and use, of the 7 basic quantities set in international units in the form of length, temperature, mass, time, electric current, light intensity and amount of substance, for the area in Situbondo district only 5 basic quantities are often found in Daily life includes length, temperature, mass, time and the strength of electric current.

A simple example of using a basic measurement tool is students on campus who still use a ruler (ruler) to work on problems related to drawing or others. Not only that, schools and universities have laboratories where in the laboratory there are various tools, including measuring basic quantities such as:

  • thermometer
  • Vernier calipers
  • micrometer
  • screw
  • stopwatch
Quantity and Unit

A. Definition of Quantity and Unit

Quantity is anything that can be measured, counted, has value and units.

Unit is a comparison in a measurement of quantity. Each quantity has its own unit.

Also Read: Multiple Choice Questions of Quantity and Units [+Pembahasan]

B. Grouping of Quantities and Units

Based on the direction and value, the quantities are grouped into two, namely:

  • scalar quantity, i.e. a quantity that has only value without direction. Examples: mass, length, time, energy, work, temperature, speed and distance.
  • vector quantity, that is, a quantity that has both a value and a direction. Example: force, weight, current, velocity, acceleration and displacement.

Based on how to obtain it can be grouped into 2 kinds, namely:

  • Quantity Physics that is the quantity obtained from the measurement. Because it is obtained from measurements, there must be a measuring tool. An example is mass. Mass is a physical quantity because mass can be measured using a balance.
  • Quantity non physics namely the quantity obtained from the calculation. In this case, a measuring instrument is not needed but a calculating tool such as a calculator. An example of a non-physical quantity is Amount.

Based on the type of unit, quantities are divided into 2 including:

  • Principal amount is a quantity that is determined in advance based on the agreement of physicists, based on SI (International System) units of basic quantities, namely:

In the International system (SI) there are: 7 dimensional base quantities and 2 additional dimensionless units.

BASE QUANTITY SI UNIT
Name Symbol Dimension Formula
Long meters m L
Mass Kilogram kg M
time Second s T
Electric current Ampere A I
Thermodynamic temperature Kelvin K q
Amount of substance Mola mole N
Light intensity Kandela CD J
ADDITIONAL HUGE SI UNIT
Flat angle radians rad
Room corner steradian sr
AMOUNT OF DESCRIPTION SI UNIT
Energy Joule J
Style newtons N
Power Watt W
Pressure Pascal Pa
Frequency Hertz Hz
Potential Difference Volt V
Electrical charge coulomb C
Magnetic flux weber Wb
Electrical resistance Farad F
Magnetic induction Tesla T
Inductance Henry Hb
light flux lumen Lm
Strong lighting Lux Lx
  • Derived quantity is a quantity that is derived from a quantity that is derived from a principal quantity. Includes:
Derived quantity

C. Examples in Daily Life

In everyday life, whether in terms of work or other activities, we usually use 5 basic quantities out of 7 basic international units, namely length, mass, time, temperature and electric current. For example, when we go to school or do assignments, we use a ruler as a measuring tool.

It’s different when we are in the market, we often see or transact directly using market scales, when we take families who have toddlers to be taken to the health center, their weight is weighed using a scale, when we are in a school or campus laboratory or researchers there we will see and use a balance of 2 arms – caliper – micrometer screw , when we go to the tailor and carpenter then we will see them using a sewing meter and a wood meter or folding meter , when we go to fish auctions we usually see hanging scales , when we are sick we are using a thermometer to see body temperature, and so on.

The following is an example of a measuring tool for basic quantities and their functions that are used in everyday life and which we often encounter in our daily lives.

Pay attention to the table:

NO. MEASURING EQUIPMENT NAME and MEASURING EQUIPMENT TYPE FUNCTION USUALLY FOUND/USUALLY SEEN
1 Ruler measuring length To measure an object whose size is Schoolchild
2 Market scales Mass measuring instruments To find out the weight of an object In the market, in the shop
3 Body scales, measuring tools for mass To find out your weight In hospitals, health centers, UKS.
4 Watches, wall clocks Measuring time To see the time At home and in hand
5 Sewing meter Length measuring tool To measure the length of an object in the form of cloth Tailor
6 Folding meter Length measuring tool To measure the length of an object in the form of wood, etc. Carpenter
7 Thermometer Temperature measuring instrument To know body temperature suhu In hospitals, health centers.
8 Stopwatch Measuring time To know the time Sports teacher, sportsman
9 caliper long measuring tool To measure small objects In the laboratory
10 Hanging scales for fish Mass measuring instrument To see the results of fish weight At the fish auction
11 Micrometer screw Length measuring tool To measure objects that are very small in size In the laboratory
12 Voltmeter An instrument for measuring electric current To measure electric voltage Engineering people who work at PLN, computers in schools.

D. Error In Measurement

The error in measurement is the deviation of the measured value from the correct value of x0. Errors can be classified into four groups:

1. Negligence

Generally caused by limitations on observers, including lack of skill in using instruments, especially for sophisticated instruments that involve many components that must be adjusted or errors in making small scale readings.

2. Systematic error

Is an error that can be stated in the form of numbers (quantitative), for example: error in measuring length with a mist of 1 mm, caliper, 0.1 mm and 0.01 mm screw micrometer

3. Random error

An error that can be expressed in the form of a number (qualitative),

Example:

  • observer error in reading length measurement results
  • Ignoring the effect of air friction on a simple swing experiment
  • Neglecting the mass of the rope and the friction between the rope and the pulley in Newton’s second law experiment.

4. Uncertainty in Measurement

When measuring a physical quantity using an instrument, it is not possible to get the correct value X0,but there is always uncertainty. This uncertainty is caused by several things, for example the accuracy limit of each tool and the ability to bring results indicated by the measuring instrument.

E. Conclusion

In everyday life, humans cannot be separated from measuring tools. Measuring tools are needed and used every day to make human work easier. Various kinds of measuring tools also vary and according to their respective functions. Measuring instruments that are often used and encountered in everyday life are measuring instruments for basic quantities in the form of length, mass, temperature, time and current strength.

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