1. Introduction and Dimensional analysisRevF2014.pptx

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CHAPTER ONE:

Introduction

1. Definition of Physics 2. Characteristics

3. Branches

4. Models, Theories, Laws 5. Measurement

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CHAPTER OBJECTIVES

At the end of this chapter, you should be able to

1) Define PHYSICS;

2) Explain MEASUREMENT;

3) Apply Unit Conversions in problem solving.

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1. WHAT IS PHYSICS??



The “SCIENCE OF

the UNIVERSE”



The most

fundamental and

basic of all the

sciences



Physics is all

about

MATTE R

TIME

SPACE ENERG

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Physics as a Science

SCIENCE

 _{from Latin word}_{“scientia”}_meaning_{“knowledge”}  _{a systematized knowledge derived from}

observation, study, facts, and principles.

PHYSICS

 _{derived from Greek word}_{“ta phusika”}_meaning

“natural things”

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Why study Physics?

 _{Physics, the most fundamental science, is}

concerned with the basic principles of the Universe.

 _{It is the foundation upon which the other}

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Branches of Physics



Mechanics

- deals with such ideas as

inertia, motion, forces and energy

(as

applied to solids and fluids).



Thermodynamics

- deals with the

principles on

heat flow, heat

transformations

and

temperature

measurements.



Electricity and Magnetism

- deals with

other aspects of matter and space with

emphasis on

el

ectric charge

and

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 _Optics _{- concerned with the nature and}

propagation of light

 _{Modern Physics - extension of physics on the} atomic and macroscopic level.

Relativity

Quantum Mechanics

Condensed-matter physics Nuclear physics

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“ The object of all sciences is to coordinate our experiences and to bring them into a logical system.”

Every Science…. Scientific Method:

Chooses to study a class of

phenomena

Describe in a systematic way

‘explain’ in terms of principles Collection of Data Application of Laws and Equations

Formulation of a Model, Theory or

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Models – Theories –

Laws



MODELS

-

mental image

of a phenomena in terms

of something we are familiar with. Or they are

mathematical representation of natural processes

e.g. Water quality models: PESTFADE (Clemente,

1991, 1993, 1998, 2007)

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 _THEORIES_{- attempt to solve a set of problems, often with}

mathematical precision.

 _{A theory is valid as long as there is no evidence to dispute it}

e.g. Darcy theory (1875) on water flow:

V = -Ki

V = ground water flow velocity K = hydraulic conductivity

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 _{LAWS - Takes the form of}_{equations or}_general

statements how nature behaves.

e.g. 2nd Law of Newton:

F = ma

F = force m = mass

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Science and

measurement

 _{The ability not only to define, but to}_measure_{is a}

requisite of science

 _In _Physics_{, more than in any other field of}

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Describing Physical

Phenomenon

PHYSICAL QUANTITY

any number that is used to describe a physical phenomenon quantitatively.

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NATURE OF PHYSICAL

QUANTITIES



Fundamental Quantities – quantities that exist by

themselves.

 _{Time, Length, Mass}



Derived Quantities – quantities that are dependent

on other quantities.

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THE SEVEN FUNDAMENTAL

QUANTITIES

FUNDAMENTAL QUANTITIES DISTANCE (m) TIME (s)

MASS (kg)

TEMPERATURE (K)

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TYPES OF PHYSICAL

QUANTITIES

 _{Scalar Quantities}_{- quantities with magnitude only}

 _{Vector Quantities}_{- quantities with both magnitude}

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Physics is based on …



MEASUREMENT!

WE DISCOVER NEW THINGS

IN PHYSICS BY

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Do you know how to measure?



We have all measured something at one

point in our lives

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Measurements

►

Standards

-

we can refer to standards as

the

reference

from which

you will compare your

physical quantity of interest

Standards

UNITS

The problem here is that

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system OF units



SI (Système Internationale)

is the system universally used by the

scientific community

SI

Eng lish

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► _{SI units are the one commonly used in physics, the one} in which meter, kilogram and second are the

fundamental units (also called mks system)

► _{One variant of SI is the so called “}_Gaussian_{“ or the}_cgs

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SI Units

Time: unit 1 second: defined as time for a certain excited atom (cesium) to make a

specified number of oscillations.

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SI Unit: Mass

 _{The unit of}_mass_{is the} kilogram, defined as the mass of a chunk of

platinum in Paris, shown here.

 _From:

http://en.wikipedia.org/wik i/File:CGKilogram.jpg

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Measurement

INSTRUMENTS

 _{Measurement instruments,}_when

calibrated in terms of the standard, give a very good approximation of the

standard!

 Remember to choose measurement instruments wisely

- not all instruments that can measure length, can actually or realistically measure length.

 For example, try using a ruler to measure the distance

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Measurement

attributes

 _Precision

Degree of fineness of a measurement

Described in terms of per cent difference relative to mean value

 _Accuracy

Degree of closeness or agreement of one measurement to a known standard value

Described in terms of per cent error relative to standard value

 _Uncertainty

Degree of error associated with measurement and the instrument. But human related errors are not considered source of uncertainty.

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Something Important

 The Magnitude of all values of physical quantities must

contain the NUMERICAL VALUE AND THE CORRESPONDING

UNIT, FOR IT TO HAVE SIGNIFICANCE OR MEANING.

3.75? kg? 3.75kg?

WHAT IS THE MASS OF THIS METAL BLOCK?

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Measurements

 _{It is better to use prefixes in}

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Unit Conversion

 _{WHAT IF... You are driving}

along a highway and you see a sign that says “SPEED LIMIT 55 mi/h” and your speedometer indicates that your speed is about 80 km/h, ARE YOU OVERSPEEDING???

 This presents some problem

 Although mi/h and km/h are both

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Unit Conversion

 _{Similar units of measures can be easily converted to}

its equivalent, by using a conversion factor

All conversion factors should have a value of 1. In the mks,

1 m = 3.28 ft = 39.37 in = 100 cm 1 kilogram = 2.2 lbs = 1000 g

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Conversions

 _When_units _are _not _consistent_{, you may need to}

convert to appropriate ones

 _{Units can be treated like algebraic quantities that}

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UNIT CONVERSION

There are three types of conversion

1. Straight forward Linear Conversion

2. Chain Conversion

3. Power Conversion

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Example:

A car accelerates at 12 mi/hr∙s. Write the acceleration in m/s2. (use 1.609 km = 1 mile)

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Example

The speed of a 2.0 kg ball is 450 km/h. Determine its speed in

a. m/s b. ft/s

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Solution

km/h m/s

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Solution

km/h ft/s

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DIMENSIONAL

ANALYSIS IS…



Is a process of

algebraic

manipulation

of physical

quantities,

considering

only the units

We often use this to check for errors in

our calculations by confirming the

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

In physics, we often encounter formulas and

equation when solving problems.



Always remember that

equations should always

be dimensionally consistent

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DIMENSIONAL

ANALYSIS



Both sides of equation must have the same

dimension

 _{Adding two physical quantities only makes sense if}

the quantities have the same dimension… (Think of the sum of two apples and one guava and one

basketball)



So, quantities

are added/subtracted

only

if

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Symbols of some physical

quantities

Quantit

y

Dimensio

n

Unit

Length

L

Meter (m)

Mass

M

Kilogram

(kg)

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Example

Determine the dimension of the quantity a. v = at

b. x = x_o + v_ot + (½) a t2 c. D = m/V

where

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 _{Determine the dimension of the quantity called}

Kinetic Energy given that

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EXAMPLE: TO THE LEFT, TO THE

RIGHT

 _{Make an equation with the following specifications:}

1. At the left hand side is W and X (Work, same dimensions as energy [ML2/T2], X is distance)

2. At the right hand side is mass (m) and acceleration (a)

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Example

 _{Determine the dimensions of the Universal}

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http://en.wikipedia.org/wiki/File:CGKilogram.jpg