Units and Dimensions

Topics-

Doing Physics

Realms of Physics

Measurement and Units

Dimensional Analysis

Significant digits

UNITS & DIMENSIONS

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Doing Physics• Physics is the study of the fundamental laws of nature.

• These laws help us to understand the physical universe.

• Physics is also the study of the behavior and structure of matter and how matter and energy are related to each other.

• The word “physics” has originated from the Greek word ”physic” which means “nature”.

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The scientific inquiry has been refined through the ages and the pattern developed to find out the solutions is called the scientific method.

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Physics, Technology and Society

Physics is a basic, fundamental science. It is interconnected with all other natural sciences such as chemistry, and biology. We may find that many technological advances based on these sciences have roots in physical laws.

Shows the highly precise and convenient laser eye surgery which has repaired the eyesight of millions around the world.

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Solar power and wind power promising the clean fuel for future

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Realms of Physics• Studying “everything” is a bit of a challenge

– Divide physics into different areas of study:

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Fundamental and Derived Quantities

We can conveniently classify physical quantities into two categories: fundamental and derived quantities.

System of Units A complete set of units, both fundamental and derived, for all kinds of quantities is called a ‘system’ of units. (a)The FPS System. The FPS system uses foot as a unit of length, the pound as a unit of mass and the second as a unit of time.

(b) The CGS System. The CGS system uses centimetre as a unit of length, the gram as a unit of mass and the second as a unit of time.

(c) The MKS system. The MKS system is a system of units based on the metre, the kilogram and the second as the units of length, mass and time respectively.

This system was adopted by the International Electrotechnical Commission and was put into universal use on 1st January, 1940.

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The International System of Units; the SI UnitsThe SI is an extension and refinement of the various traditional forms of the metric system. The name SI is an abbreviation for système International d’ unites,

The SI has seven primary or fundamental units

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Length

Distance Length (m)Radius of Visible Universe 1 x 1026

To Andromeda Galaxy 2 x 1022

To nearest star 4 x 1016

Earth to Sun 1.5 x 1011

Radius of Earth 6.4 x 106

Sears Tower 4.5 x 102

Football Field 1.0 x 102

Tall person 2 x 100

Thickness of paper 1 x 10-4

Wavelength of blue light 4 x 10-7

Diameter of hydrogen atom 1 x 10-10

Diameter of proton 1 x 10-15

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MassObject Mass (kg)

visible universe ~ 1052

Milky Way galaxy 7 x 1041

Sun 2 x 1030

Earth 6 x 1024

Boeing 747 4 x 105

Car 1 x 103

Student 7 x 101

Dust particle 1 x 10-9

Bacterium 1 x 10-15

Proton 2 x 10-27

Electron 9 x 10-31

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TimeInterval Time (s)

Age of Universe 5 x 1017

Age of Grand Canyon 3 x

1014

Avg age of college student 6.3 x 108

One year 3.2 x 107

One hour 3.6 x 103

Light travel from Earth to Moon 1.3 x 100

One cycle of guitar A string 2 x 10-3

One cycle of FM radio wave 6 x 10-8

One cycle of visible light 1 x 10-15

Time for light to cross a proton 1 x 10-24

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The Multiples and Submultiples in SIWhen the SI units are either too large or too small in reference to a particular physical quantity, their multiples or submultiples in powers of ten are used. The table, given below, gives standard names of the multiples and submultiples which can be prefixed to the name of the unit concerned: