CHAPTER 1

MAIN QUANTITY AND DERIVED QUANTITY

PHYSICS FOR JUNIOR HIGH SCHOOL VII

Something measurable stated in number

(quantitative), for instance: length, mass, time, temperature, etc.

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QUANTITY

MAIN QUANTITY

DERIVED QUANTITY

QUANTITY

MAIN QUANTITY

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Main quantity is a quantity that its unit is determined first, or a quantity that its unit is defined especially based on international conference.

There are 7 main quantities

Quantity Unit Unit Symbol

length Meter M

Mass Kilogram Kg

Time Second S

Electric currency Ampere A

Temperature Kelvin K

Substance Amount Mole Mole

Light Intensity Candela Cd

PHYSICS FOR JUNIOR HIGH SCHOOL VII

DERIVED QUANTITY

Derived quantity is a quantity that can be derived or taken from main quantities

Derived quantities and their units

Quantity Unit Symbol

Area A M2

Volume V M3

Velocity V M/s or m.s–1

Acceleration A M/s2 or m.s–2

Force F Kg.m/s2 or kg.m.s–2

Work W Kg.m2/s2 or kg.m2.s–2

Power P Kg.m2/s3 or kg.m2.s–3

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THE INTERNATIONAL UNIT

THE INTERNATIONAL UNIT OF LENGTHThe unit of length is meter 1 meter = The space of two scratches on standard meter bar that is made of the compound of platinum-iridium. It is kept in the International Bureau of Weights and Measures (Sevres, Frances)

on November in1983, the definition of meter standard was changed, it was determined that 1 meter is the travelled distance of light (in vacuum) in duration of 1/299.792.458 second

PHYSICS FOR JUNIOR HIGH SCHOOL VII

THE INTERNATIONAL UNIT

THE INTERNATIONAL UNIT OF MASS

The standard unit of mass is kilogram, which means the mass of a platinum-iridium cylinder that is kept in Bureau of Weights and Measures (Sevres, France). The international derived mass standard for U.S.A called prototype kilogram Number 20, kept in a dome in Bureau of National Standard

The standard kilogram number 20 that is kept in the bureau of national standard of U.S.A is a platinum cylinder, kept under the two bell-shaped glass domes (Sources: Serway and Jewett, Physics for Scientists and Engineers, 6th edition, 2004)

PHYSICS FOR JUNIOR HIGH SCHOOL VII

INTERNATIONAL UNIT

INTERNATIONAL UNIT OF TIME

The standard for time is second (s). 1 second is defined as the duration that is needed by cesium atom-133 for vibrating 9.192.631.770 times in transition between two energy level in its basic energy

PHYSICS FOR JUNIOR HIGH SCHOOL VII

UNIT CONVERSION

UNIT CONVERTION OF LENGTH, MASS, AND TIME

Unit Conversion of length and Mass

1. 2,5 km = ... m2. 1.500 cm = ... m3. 2.000 g = ... kg4. 4,25 g = ... mg

ExampleConvert the following units !

answer :1. 2,5 km = 2,5 × 1.000 m = 2.500

m2. 1.500 cm = 1.500 × 1/100 m = 15 m3. 2.000 g = 2.000 × 1/1.000 kg = 2 kg4. 4,25 g = 4,25 × 1.000 mg = 4.250

mg

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UNIT CONVERSION

Unit conversion of time

ExampleConvert the following units !

1. 1,5 hours = ... minutes2. 360 seconds = ... minutes

1. 1,5 hours = 1,5 × 60 minutes = 90 minutes2. 360 seconds = 360 × 1/60 minutes = 6 minutes

Answer :

1 hour = 60 minutes or 1 minute = 1/60 hour

1 minute = 60 seconds or 1 seconds = 1/60 minute

1 hour = 3.600 seconds or 1 second = 1/3.600 hour

PHYSICS FOR JUNIOR HIGH SCHOOL VII

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