Physic first lesson

1. Helmand University
Engineering Faculty
Electric Department
Lecturer: Eng. Mohammad Kazim Karimi
Chapter 1
Physics and Measurement
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2. Table of Contents
1. Introduction
2. Standards of Length, Mass, and Time
3. Modeling and Alternative Representations
4. Dimensional Analysis
5. Conversion of Units
6. Significant Figures
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3.  Fundamental Science
• Concerned with the fundamental principles of the Universe
• Foundation of other physical sciences
• Has simplicity of fundamental concepts
 Divided into six major areas
1. Classical Mechanics : Concerning the motion of objects that are
large relative to atoms and move at speeds much slower than the
speed of light.
2. Relativity :Deals with the movement of objects at any speed
even moving with the speed of light.
3. Thermodynamics: Dealing with heat, temperature, and work of
the systems.
4. Electromagnetism: Concerning electricity, magnetism and
electromagnetic fields.
5. Optics: The study of the behavior of light and its interaction with
materials.
1. Introduction
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4. 1. Introduction
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6. Quantum Mechanics: A collection of theories connecting the
behavior of matter at the submicroscopic level to macroscopic
observations.
 Objectives of Physics
• To use these laws to develop theories that can predict the results of
future experiments.
• Express the laws in the language of mathematics
• Mathematics provides the bridge between theory and experiment
 Measurements
• Used to describe natural phenomena
• Needs defined standards
• Characteristics of standards for measurements

5. 2.Standards of Length, Mass, and Time
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 Standards of Fundamental Quantities
• Standardized systems Agreed upon by some authority, usually a
governmental body
• SI – (System International) Agreed to in 1960 by an international
committee Main system used in this text
Quantity SI Unit
Length meter
Mass kilogram
Time second
Temperature Kelvin
Electric Current Ampere
Luminous Intensity Candela
Amount of Substance mole

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 In mechanics, three basic quantities are used
1. Length
2. Mass
3. Time
 Length
• Length is the distance between two points in space (Units SI
meter m)
• The basic unit of length, meter(m) was redefined as the distance
traveled by light in vacuum during a time of 1/299 792 458
second.

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 Mass
• The mass of an object is related to the amount of material that is
present in the object Units (SI – kilogram, kg)
• The mass of a specific platinum–iridium alloy cylinder kept at the
International Bureau of Weights and Measures at Sevres, France.
2.cont….

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 Time
• Before 1967, the standard of time was defined in terms of the mean
solar day. (Units seconds)
2.cont….

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 Prefixes
 Prefixes correspond to powers of 10
 Each prefix has a specific name
 Each prefix has a specific abbreviation
 Examples:
 1 mm = 10-3 m
 1 mg = 10-3 g
2.cont….

10. 3.Modeling and Alternative Representations
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 A model is a simplified substitute for the real problem that allows
us to solve the problem in a relatively simple way.
 This replacement of an extended object by a particle is
called the particle model, which is used extensively in physics.
1. Mental representation
2. Pictorial representation
3. Simplified pictorial representation
4. Graphical representation
5. Tabular representation.
6. Mathematical representation

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Solution

12. 4. Dimensional Analysis
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 Dimension has a specific meaning – it denotes the physical
nature of a quantity
 Dimensions are denoted with square brackets
Length [L] Mass [M] Time [T]

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 Dimensional Analysis
 Technique to check the correctness of an equation or to assist in
deriving an equation
 Dimensions (length, mass, time, combinations) can be treated as
algebraic quantities
 add, subtract, multiply, divide
 Both sides of equation must have the same dimensions
 Any relationship can be correct only if the dimensions on both sides
of the equation are the same
 Cannot give numerical factors: this is its limitation
 Given the equation: x = ½ at 2
L
T
T
L
L 2
2




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Cont.

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16. 4. Conversion of Units
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 Sometimes it is necessary to convert units from one measurement
system to another or convert within a system (for example, from
kilometers to meters).
 Conversion factors between SI and U.S. customary units of length

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18. 5. Estimates and Order-of-Magnitude Calculations
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 The estimate may be made even more approximate by expressing it
as an order of magnitude, which is a power of 10.
1. Express the number in scientific notation, with the multiplier of the
power of 10 between 1 and 10 and a unit.
2. If the multiplier is less than 3.162 (the square root of 10), the order
of magnitude of the number is the power of 10 in the scientific
notation. If the multiplier is greater than 3.162, the order of magnitude
is one larger than the power of 10 in the scientific notation.
 Suppose someone asks you the number of bits of data on a typical
Blu-ray Disc. In response, it is not generally expected that you
would provide the exact number but rather an estimate, which may
be expressed in scientific notation.

19. 6. Significant Figures
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 The number of digits that have merit in a measurement or
calculation.
 When writing a number, all non-zero digits are significant.
 Zeros may or may not be significant.
a. those used to position the decimal point are not significant (unless
followed by a decimal point)
b. those used to position powers of ten ordinals may or may not be
significant.
Examples:
2 1 sig fig
40 ambiguous, 2 sig figs(use scientific notations)
4.0 x 10 2 significant figures
0.0031 2 significant figures
3.03 3 significant figures

20. Cont…
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 When multiplying several quantities, the number of significant
figures in the final answer is the same as the number of significant
figures in the quantity having the smallest number of significant
figures. The same rule applies to division.
 When numbers are added or subtracted, the number of decimal
places in the result should equal the smallest number of
decimal places of any term in the sum or difference.

21. Cont.
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Homework !
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1. Give full description by your own words.
2. Solve (1-7 )Problems.

22. Cont.
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Print pages(1-284)

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