Quantities, Units, And Measurement

Quantities, Units, and Measurement A. Definition Of Quantities, Units, and Measurement  Quantities are everything that can be measured, has value that can be expressed by numbers, and has the certain units.  Units are a statement that explains the meaning of a quantity.  Measurement is a process of comparing something measured with another as measures made as a standard. In other words, measurement is the process of comparing a quantity with another quantity which is used as unit. A. Basic Quantities  Quantities which are usually used in physics are differentiated into two, those are basic quantities and derived quantities. Basic quantities are quantities the units of which are predetermined and they are not derived from another quantities.  Basic quantities consist of seven quantities : No. Basic Quantities Units Units Name Symbol 1

Length

meter

m

2

Mass

kilogram

kg

3

Time

second

s

4

Electric Current

ampere

A

5

Temperature

Kelvin

K

6

Luminous Intensity

candela

cd

7

The amount substance

mole

mol

of

Units which are not acknowledged internationally are called non-standard units. Hence, it is necessary to be determined a unit system that is valid in-ternationally functioning as standard units (or also called fundamental units).  Some scientists organized international conference which agreed standard units called International System Units (SI). 

1. Length  Length is the distance between two points in a space. According to SI units, the length quantity is expressed in meter.  There are several kinds of measuring devices used to measure quantity of length, among others, are as follows. a) Ruler The ruler uses cm or mm scale with accuracy of 0.1 cm or 1 mm. b) Vernier Caliper A vernier caliper has two main parts, namely outer jaw to measure thickness and inner jaw to measure the diameter of inner part of an object. The accuracy of the vernier caliper reaches 0.1 mm. Vernier caliper has two jaws, namely fixed jaw and sliding jaw. The fixed jaw has length scale which is called main scale, while the sliding jaw has short scale which is called vernier scale. c) Screw Micrometer A screw micrometer has accuracy until 0.01 mm. The screw mi-crometer is usually used to measure tiny or small objects. The screw micrometer has two scales, those are main scale and vernier scale. 1. Mass  The mass of a body is the amount of matter contained by the body. Accor-ding to SI units, the unit of mass is kilogram (kg).

Weight in physics has different definition to the weight in everyday life. According to physics, weight is the force experienced by a body which has mass because of gravity.  Measuring device used to measure mass quantity is balances. Several kinds of balances are as follows : a) Market Balance The balance which is often found in the markets is called the market balance. b) Electronic Balance An electronic balance has a screen which will show the value of the mass of body measured automatically without need the weight of scale. The electronic balance is operated by using electrical power. 

c) Arm Balance There are several kinds of arm balance i.e. two armed balance, three armed balance, and four armed balance. The working pro-cedure of two armed balance is equal to market balance. Mean-while, the working procedure of four armed balance is by regulating sliding load found in the base of the balance, so scale points to the number zero when there is no yet the body to be measured. 1. Time  Time unit in SI is expressed in second.  Meanwhile time units usually used everyday are as follows : a) 1 minute = 60 s b) 1 hour = 60 x 60 s = 3.600 s c) 1 day = 24 x 3.600 s = 86.400 s  The time measuring device usually used in ancient were hourglasses and sundial. Nowadays, the devices usually used as time measurer are watch and stopwatch. a) Watch Commonly, watches have three hands, those hour hand, minute hand, and second hand.

b) Stopwatch Stopwatch is usually used in a laboratory or sport activities that is to measure time interval of an event that activities. There is a stopwatch using hands to show its time, but there is also a digital stopwatch. A. Derived Quantities  Derived quantities are quantities derived from basic quantities.  Several Examples of Derived Quantities : No Derived Units Name Units . Quantities Symbol square meters

m2

1

Area

2

Volume

cubic meters

m3

3

Velocity

meters per second

m/s

4

Force

newton

5

Density

kilograms per cubic meters

6

Power

watt

W

7

Work

joule

J

N kg/m3

1. Area  Area is derived quantity which is obtained by multiplying two length quantities.  To measure the area of regullar shape of object we use ruler, etc.  To measure the area of irregular shape of object we use graph paper. Example : – Count the full square cover with object =3 – Count the square half and most than half cover of object = 4 – The value of ones = 3 + 4 = 7

1.

Volume  Volume is the number of spaces used by a body. Similar to area, volume is also derived of basic quantities, that is the product of three length quantities.  To measure volume of regular shape, their volume can be calculated by u-sing certain formula.  To measure volume of irregular shape or liquid we use measuring cylinder Example :

–

–

–

 We

can

Pour some water into the measuring cylin-der. Write volume of water = V1 Fill the object into the measuring cylinder. Write volume of water = V2 Volume of object = V2 - V1

measure volume of irregular displacement method too. displace glass

? = V object

shape

by

A. Working In The Laboratory  In learning physics, besides learn theory in a class you need also to do several experiments/practicums in a laboratory to apply or prove the theories obtained in the class. 1. Laboratory Equipment  In a laboratory there are found devices and material to do a practicum. Devices usually found in a physics laboratory are balances, thermo-meter, stopwatch, ruler, vernier caliper, glasses, glass jars, bunsen bur-ner, reaction tubes, and so on. Meanwhile the materials usually found in the laboratory are chemicals. 1. Working Safety  Practicum in a laboratory closely relates to devices and materials which sometime can cause any accident if it is done by inappropriate method.  It is necessary to be considered the use of those devices and materials, so not happen any accident when doing practicum, because working sa-fety in the laboratory is an important factor for everyone. Besides that, it is necessary also to understand the meaning of symbols or signs which are usually written in the package of chemicals or the certain devices, among others, are as follows :

 The things that must be considered in doing practicum in a laboratory are as in the below : a) Plan the experiment which will be done before starting the practicum. b) Prepare the things required and what must be considered before en-tering the laboratory such a note book, the kind of experiment, the kind of materials, the kind of devices, and the methods to remove the waste of the experiment remain. c) Master the working procedure and ask your teacher if you have any doubt or do not know about something. d) Wear a coat and goggle while you are doing an activity. They are u-seful for protecting our skin, eyes, and other body parts from a ha-rmful chemical substance. e) Do not wear a sandal or opened shoes or highly sole shoes. f) Fit your hair if your hair is long. g) Do not eat or drink while you are in the laboratory. h) Keep the cleanness of a practicum desk. If the practicum desk is wet, immediately dry it using a napkin. i) Avoid direct contact with chemical stuffs. j) Do not smell a chemical substance directly from a bottle nozzle. k) Make sure the gas tap is not leak when using bunsen. l) Make sure the water and gas taps are always in closed position befo-re and after practicum is finished. m)Do not work alone in the laboratory, minimally there is a teacher ob-serving. n) Do not plat with a laboratory equipment and a chemical stuff. o) Do not make mistake among friends.

p) If your body is splashed by a certain chemical substance, wash it with water as much as possible. q) If accident happen, immediately contact paramedics. r) Devices used in practicum must be kept well as possible, do not until be broken.