Engineering Physics
‫الفيـــــــــــــــــــــــزياء‬
1: What is Physics?
It is the most basic science. It concerns the
behavior and structure of matter.
‫هو أكثر العلوم األساسية ويتعلق بسلوك وتركيب الماده‬
Importance of physics:‫أهمية الفيزياء‬
Physics is a wide branch and has many
application in all other branches as computer
science, medicine, engineering, pharmacy,
etc…
Physics:-
Classes of Physics:
‫اقسام الفيزياء‬
1-Classical physics: It concerns motion, fluids,
heat, sound light, electricity and magnetism.
‫ المغناطيسية‬-‫ الكهرباء‬- ‫ الحرارة‬-‫ الموائع‬- ‫الفيزياء الكالسكية وتشمل الحركة‬
2-Modern physics : It includes relativity,
atomic, nuclear physics.
‫ الفيزياء النووية‬-‫الفيزياء الحديثة وتشمل النسبية – الذرية‬
2-Units and dimensions
‫الوحدات واألبعاد‬
Units: •
Any physical quantity is represented by two
quantities, value and unit. The value of the
physical quantity depends on its unit. For
example the velocity of a car is 90 km/h. The
velocity of the car is 25 m/s.
‫ الوحدة‬-2 ‫ القيمة‬-1 ‫أي كمية فيزيائية يعبر عنها بكميتين هما‬
)‫القيمة ألي كمية فيزيائية تعتمد علي وحدتها(أي الوحدة المقاسة بها‬
‫ثانية‬/‫ متر‬25 ‫ساعة أو سرعة سيارة‬/‫ كم‬20 ‫مثال سرعة سيارة‬
‫نظام الوحدات‬
‫‪System of units:‬‬
‫)‪1- French units (cgs‬‬
‫يقاس بالسنتيمتر‬
‫‪c‬‬
‫النظام الفرنسي وفيه يقاس الطول ورمزه ‪ L‬بالسنتيمترورمزه ‪c‬‬
‫يقاس بالجرام‬
‫‪g‬‬
‫الزمن ‪s‬‬
‫يقاس بالثانية‬
‫)‪a) Length (L‬‬
‫)‪b) Mass(M‬‬
‫الكتله‬
‫)‪c) Time (T‬‬
‫)‪2- British units (fbs‬‬
‫يقاس بالقدم‬
‫‪f‬‬
‫النظام االنجليزي وفيه يقاس الطول ورمزه ‪ L‬بالقدم ورمزه ‪f‬‬
‫يقاس بالباوند‬
‫الكتله ‪b‬‬
‫)‪b) Mass(M‬‬
‫يقاس بالثانية‬
‫)‪c) Time (T‬‬
‫الزمن ‪s‬‬
‫)‪a) Length (L‬‬
3- International units (SI) OR (MKS)
MKS ‫في النظام العالمي او الدولي او نظام‬
a)
Length (L)
b)
Mass(M)
c)
Time(T)
‫يقاس بالمتر‬
M
‫يقاس بالكيلو جرام‬
kg
‫يقاس بالثانية‬
S
Sometimes the international units SI is
called (MKS).
The SI units are commonly used , the other
systems are still in use for some limited
cases.
Types of Physical quantities: ‫انواع الكيات الفيزيائية‬The
physical quantities can be classified into two
classes: ‫الكميات الفيزيائية تقسم الي نوعين‬
1- Basic or fundamental physical quantity
‫ كميات اساسية‬-1
2- derived physical quantity.
‫ كميات مشتقه أي يمكن الحصول عليها بضرب او قسمة او جمع او‬-2
‫طرح الكميات األساسية‬
The fundamental physical quantities are only
seven physical quantities listed as:
1-Length 2- Mass 3- Time 4-Temperature 5- •
Electric current 6- quantity of material
7Luminous.
The symbols of these fundamental physical
quantities are:
1- Length (l) 2-Mass (m) 3- Time (s) 4Temperature(k). 5- Current (i) 6- Quantity of
Material (o) 7-Liuminous (c).
Any other physical quantity not included in the above
seven quantities is called derived physical quantity
‫رموز الكميات األساسية هي‬
-6 ‫التيار الكهربي‬-5 ‫ درجة الحرارة‬-4 ‫ الزمن‬-3 ‫ الكتله‬-2 ‫ الطول‬-1
‫ شدة االضاءة‬-7 ‫كمية الماده‬
‫أي كميه أخري غير الكميات السابقة تسمي كميات مشتقة‬
Force, velocity, acceleration, density, …..
are all derived physical quantities.
‫الخ جميعها‬....... ‫القوة و السرعة والتسارع او العجلة و الكثافة‬
‫كميات مشتقة أي يمكن الحصول عليها من الكميات األساسية‬
It should be noted that the derived physical
quantities are composed of fundamental
physical quantities.
-:‫ملحوظة‬
‫الكميات الفيزيائية المشتقة تتكون من الكميات الفيزيائية األساسية‬
For example density (ρ) can be written as:
ρ = mass / volume = mass / (length)**3
As shown the density is expressed in terms
of the fundamental physical quantities
mass and length.
Every derived physical quantities can be similarly
expressed in terms of its fundamental physical
quantities
‫كما يتضح الكثافة يعبر عنها بداللة الكميات األساسية وهي الكتلة‬
‫والطول‬
‫كل كمية مشتقة يعبر عنها بداللة الكميات األساسية كما بالمثال‬
‫السابق‬
-Write the following derived physical quantities
in terms of fundamental physical quantities:
Work, Energy, Electric charge, Power.
‫أكتب الكميات المشتقة التالية بداللة الكميات األساسية‬
‫ القدرة‬- ‫ الشحنة الكهربية‬- ‫ الطاقة‬- ‫الشغل‬
As the fundamental physical quantities has
units (cgs, fbs or SI), the derived physical
quantities have also the same units
‫الكميات المشتقة يكون لها نفس وحدات الكميات األساسية‬
in the three unit systems (cgs, fbs or SI). For example the units of
Force is dyne in the cgs boundal in the fbs and newton in the SI
or MKS.
‫في نظام الوحدات الثالث علي سبيل المثال وحدة القوة هي الداين في النظام الفرنسي وهي الباوندال في‬
‫النظام االنجليزي وهي النيوتن في نظام العالمي او الدولي‬
Theory of Dimensions
In the theory of dimension the fundamental physical
quantities have certain symbols and notations as
follow:
1-Length [L].
2- Mass [M].
3- Time [T].
4-Temperature [K].
5- Electric current [I].
6- quantity of material [O].
7-Luminous [C].
Thus any fundamental physical quantity is
represented by a capital letter between
two square brackets. These notations are
called the dimensions of fundamental
physical quantities.
‫أي كمية اساسية يعبر عنها بحرف كبير بين قوسين مربعين وهذا‬
‫الترقيم يسمي أبعاد الكميات الفيزيائية األساسية‬
Now to write the dimension of any derived
physical quantity one should do the
following steps:
‫األن لكي نكتب أبعاد أي كمية مشتقة سوف نتبع الخطوات التالية‬
a- Write the derived physical quantity.
b- Change the derived physical quantity into
its fundamental physical quantities.
c- Replace each fundamental physical
quantity by its notation of dimension.
d- Resultant expression is the dimension of
the derived physical quantity.
‫الخطوات‬
‫أكتب الكمية المشتقة‬-1
‫ حول الكمية المشتقة الي ما يساويها من كمية اساسية‬-2
‫استبدل كل كمية اساسية برمزها أي رمز العناصر المكونة لهاا‬-3
‫التعبير الناتج هو ابعاد الكمية المشتقة‬-4
For example to write the dimension of
acceleration a.
a- Acceleration a is rate of velocity change
i.e.
a = velocity / time.
b- Since velocity is not fundamental physical
quantity then velocity is written in terms of the
fundamental physical quantities
velocity = distance / time.
c- Then acceleration is expressed by its
fundamental physical quantities as:
a = distance / ( time * time ) = distance / time** 2
d- Finally the dimensions of acceleration are
a = [L] / [T]**2 = [L] [T]**-2
Importance of the theory of Dimensions: ‫اهمية نظرية‬
‫األبعاد‬
The study of the theory of dimensions is
very important for students, scientists,
and even for science. Following are the
importance of the theory of dimensions
‫ان دراسة نظرية األبعاد هام جدا للطالب والعلماء وأيضا للعلم‬
‫والتالي هي أهمية نظرية األبعاد‬
1- Convert between different units.
‫ التحويل بين الوحدات المختلفة‬-1
For example one can find the relation
between feet and meter.
‫تستطيع ان توجد العالقة بين القدم والمتر علي سبيل المثال‬
To find the relation between feet and meter
consider the acceleration of gravity g in the
cgs and in the fbs.
g (cgs) = 9.8 m / s**2 while g (fbs) =32 f / s**2
the dimensions of g is distance / time2 for
the two systems, then the two values are
equal.
Thus 9.8 m / s**2 = 32 f / s**2
9.8 m = 32 f
1 m = 32 / 9.8 f
= 3.265 f
2- Check any physical expression.
‫اختبار أي تعبير فيزيائي او معادلة هل صح أم خطأ‬
Any physical expression can be checked
out whether it is correct or not using the
theory of dimension.
‫أي تعبير فيزيائي يمكن اختبار صحته باستخدام نظرية األبعاد‬
This can be done by:
a- Write the expression.
b- Write the left hand side of the expression
(lhs). Write the dimension of the left hand
side.
c- Write the right hand side of the
expression (rhs). Write the dimension of
the right hand side.
d- If the expression is correct the
dimensions of the two sides should be
equal.
If not the expression is not correct.
You then can correct it.
Example:
Check the following expression
v**2 = v0**2+0.5*a* t**2
Where v and v0 are the final and initial
velocity, a is the acceleration and t is
time.
Solution:
Following the above steps:
a- The expression is
V**2 = v0**2 +0.5 *a* t**2
b- Left hand side of the expression is v**2
Dimensions are [L]**2*[T]**-2
c- Right hand side of the expression is
V0**2 +0.5*a* t**2 .
1- The first term is v0**2 has dimensions
[L]**2*[T]**-2
2- The second term is 0.5* a* t**2 has dimensions
of acceleration * time**2
= [L]* [T]**-2* [T]** 2
Thus the dimensions of the right hand side of the
expression are
[L]**2*[T]**-2 + [L] *[T]**-2 * [T]** 2
d- Compare the dimensions of the left and right
hand sides indicates that
the expression is not correct.
3- Deriving new expression.
In the following an expression for the periodic
time of a simple pendulum will be derived using
the theoryof dimensions.
Steps are as follow:
a- Assumptions: Assume the periodic time of the
pendulum is giving by t
b- Assume t depends on many factors as:
the length of the pendulum l, the mass of
the ball m and the acceleration of gravity
g.
c- Assume that t depends on ( l )a, on ( m )b
and on ( g )c.
d- Put the expression as
t = ( l )**a * ( m )**b * ( g )**c
where a, b and c are constants to be
determined..
e- From the dimensions of both sides of the
above expression the constant a, b and c
can be determined.
f- The dimensions of the lhs can be written
as: [L]**0[M]**0 [T]**1.
g-The dimensions of the rhs can be written
as: [L]**a*[M]**b*[L]**C[T]**-2c =[L]**(a+c)
[M]**b *[T]**(-2c)
h- Compare between the dimensions of
each physical quantity lhs with rhs.
i- [L]**0 = [L]**( a+c) Thus a = -c
[M]**0 = [M]**b then b=0
and [T] = [T]-2c Then c= -1/2 and a = 1/2
Finally the expression for the periodic time
of a simple pendulum can be written as:
t α ( l )** ½* ( m )**0 *( g )**( -1/2) or
t = 2 π √(l / g )
where 2π is the proportionality constant
and it can be determined experimentally.
4-Determination of the units of the physical
constants.
There is a common mistake that any
physical constant is a dimensionless
quantity. This is not generally correct.
There are some constants have no
dimension but most of other constants
have Dimension
For example
the gravitational force between two masses
M1 and M2 and the distance between
them is d is represented as
F α M1 F α M2 F α 1 / d2
F = G* (M1 x M2 / d2)
where G is the proportionality constant and
called gravitational constant.
To find units of G one should find the
dimensions of the lhs which is force as
given before the dimensions of force is
[M][L][T]-2. The dimensions of the rhs are
[M]2[L]-2. It is clear that the dimensions
are not the same.
Thus G has dimensions [M][L][T]**-2 /
[M]**2[L]**-2. Finally the units of G is
Newton meter** 2 / kg**2.
It should be noted that :
1- Physical quantities of different dimensions as
( kg + m + sec ) can not be added
2- Any physical quantity of different formula have
the same dimensions as area ( of square or
triangle or circle ) has Dimensions [L]2.
3- The power of any exponential is dimensionless
as :- e** ( ab/cd ) where ab/cd has no dimensions.
4-Numerical quantities and values are
dimensionless.
Mass
It measure the quantity of matter on an
object
Inertia
It is the resistance of any object to change
its state of motion or rest.
Inertial Mass
Quantitatve measure of an object’s
resistance to acceleration
Weight
It is the force on an object due to gravity
Motion
It is a change in position of an object with
respect to time
Newton
In SI unit of force kg.m/s2 or
The amount of net force required to
accelerate a mass of 1 kg at a rate of
1m/s2
Dyne
French system unit of force g.cm/s2 or
The force required to accelerate a mass of 1
gm at a rate of 1cm/s2
g=9.81 m/s2 &g=32 ft/s2
1N = 10**5 Dyne
1m= 3.265 f
1kg = 2.2Ib mass
1 Ibf =4.45 N
1 Slug = 32.2 ib Mass