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Engineering Physics

Engineering Physics. Physics :- الفيـــــــــــــــــــــــزياء 1: What is Physics? It is the most basic science . It concerns the behavior and structure of matter. هو أكثر العلوم الأساسية ويتعلق بسلوك وتركيب الماده Importance of physics:- أهمية الفيزياء

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Engineering Physics

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  1. Engineering Physics Physics:- الفيـــــــــــــــــــــــزياء 1: What is Physics? It is the most basic science. It concerns the behavior and structure of matter. هو أكثر العلوم الأساسية 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…

  2. Classes of Physics:اقسام الفيزياء 1-Classical physics: It concerns motion, fluids, heat, sound light, electricity and magnetism. الفيزياء الكلاسكية وتشمل الحركة - الموائع- الحرارة - الكهرباء- المغناطيسية 2-Modern physics : It includes relativity, atomic, nuclear physics. الفيزياء الحديثة وتشمل النسبية – الذرية- الفيزياء النووية

  3. 2-Units and dimensionsالوحدات والأبعاد • 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. أي كمية فيزيائية يعبر عنها بكميتين هما 1- القيمة 2- الوحدة القيمة لأي كمية فيزيائية تعتمد علي وحدتها(أي الوحدة المقاسة بها) مثال سرعة سيارة 20 كم/ساعة أو سرعة سيارة 25 متر/ثانية

  4. System of units:نظام الوحدات 1- French units (cgs) a) Length (L) يقاس بالسنتيمتر c النظام الفرنسي وفيه يقاس الطول ورمزه L بالسنتيمترورمزه c b) Mass(M) يقاس بالجرام g الكتله c) Time (T)يقاس بالثانية s الزمن 2- British units (fbs) a) Length (L) يقاس بالقدم f النظام الانجليزي وفيه يقاس الطول ورمزه L بالقدم ورمزه f b) Mass(M) يقاس بالباوند b الكتله c) Time (T)يقاس بالثانية s الزمن

  5. 3- International units (SI) OR (MKS) في النظام العالمي او الدولي او نظام MKS • Length (L) يقاس بالمتر M • Mass(M) يقاس بالكيلو جرام kg • Time(T) 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.

  6. 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 1- كميات اساسية 2- derived physical quantity. 2- كميات مشتقه أي يمكن الحصول عليها بضرب او قسمة او جمع او طرح الكميات الأساسية The fundamental physical quantities are onlyseven physical quantities listed as: • 1-Length 2- Mass 3- Time 4-Temperature 5- Electric current 6- quantity of material 7-Luminous.

  7. The symbols of these fundamental physical quantities are: 1- Length (l) 2-Mass (m) 3- Time (s) 4-Temperature(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 الأساسية هي 1- الطول 2- الكتله 3- الزمن 4- درجة الحرارة 5-التيار الكهربي 6- كمية الماده 7- شدة الاضاءة أي كميه أخري غير الكميات السابقة تسميكميات مشتقة

  8. Force, velocity, acceleration, density, ….. are all derived physical quantities. القوة و السرعة والتسارع او العجلة و الكثافة .......الخ جميعها كميات مشتقة أي يمكن الحصول عليها من الكميات الأساسية It should be noted that the derived physical quantities are composed of fundamental physical quantities. ملحوظة:- الكميات الفيزيائية المشتقة تتكون من الكميات الفيزيائية الأساسية For example density (ρ) can be written as: ρ = mass / volume = mass / (length)**3

  9. 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 بدلالة الكميات الأساسية وهي الكتلة والطول كل كمية مشتقة يعبر عنها بدلالة الكميات الأساسية كما بالمثال السابق

  10. -Write the following derived physical quantitiesin terms of fundamental physical quantities: Work, Energy, Electric charge, Power. أكتب الكميات المشتقة التالية بدلالة الكميات الأساسية الشغل - الطاقة - الشحنة الكهربية - القدرة 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 الأساسية

  11. in the three unit systems (cgs, fbs or SI). For example the units of Force is dyne in the cgs boundal in the fbs andnewton in the SI or MKS. في نظام الوحدات الثلاث علي سبيل المثال وحدة القوة هي الداين في النظام الفرنسي وهي الباوندال في النظام الانجليزي 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].

  12. 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 الأساسية Now to write the dimension of any derived physical quantity one should do the following steps: الأن لكي نكتب أبعاد أي كمية مشتقة سوف نتبع الخطوات التالية

  13. 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 1-أكتب الكمية المشتقة 2- حول الكمية المشتقة الي ما يساويها من كمية اساسية 3-استبدل كل كمية اساسية برمزها أي رمز العناصر المكونة لهاا 4-التعبير الناتج هو ابعاد الكمية المشتقة

  14. 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

  15. Importance of the theory of Dimensions:اهمية نظرية الأبعاد 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 الأبعاد هام جدا للطلاب والعلماء وأيضا للعلم والتالي هي أهمية نظرية الأبعاد 1- Convert between different units. 1- التحويل بين الوحدات المختلفة For example one can find the relation between feet and meter. تستطيع ان توجد العلاقة بين القدم والمتر علي سبيل المثال

  16. 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

  17. 2- Check any physical expression. اختبار أي تعبير فيزيائي او معادلةهل 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 نظريةالأبعاد This can be done by:

  18. 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.

  19. 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

  20. 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.

  21. 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.

  22. 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)

  23. 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.

  24. 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

  25. F α M1 F α M2 F α 1 / d2 F = G* (M1 x M2 / d2) where G is the proportionality constant andcalled 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.

  26. 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.

  27. 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

  28. 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

  29. 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

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