PH Welcome to IIT Madras and welcome to PH 1010 Course. A few Dos and Don ts in this Course

Transcription

1 PH 1010 A Batch Teacher : Dr.A.Subrahmanyam Welcome to IIT Madras and welcome to PH 1010 Course A bit of Introduction about the Course A few Dos and Don ts in this Course 1

2 Please remember that ALL of you equally competent So you are all here You all have done enough of Physics and Solved very many problems All of you have toiled for the JEE and other Examinations If you are not intelligent, you will not be here You are here with a great ambition of learning You are all here with iha specific purpose : of getting a good B Tech Degree of world standard We want to see you as GOOD ENGINEERS The foundation of Good Engineering is good, clear basic Physics 2

3 I wish to remind you a few important points about the teaching and about the course We teach concepts This is the reason why YOU SHOULD ATTEND ALL THE CLASSES Attendance is COMPULSORY. If you are absent to more than 15% of the classes, You will NOT BE ELIGIBLE to Write the exams. The exams will be only Problems or short answer type questions based on what has been taught in the class and Tutorials. There will be questions in the exams based on Lectures and Tutorial sheets. 3

4 Our Class Time Table : Class Room : CRC 101 Monday : TUTORIAL : 4 th Hour Tuesday : Lecture : 3 rd Hour Wednesday : Lecture : 2 nd Hour : Hrs : Hrs : Hrs We propose to conduct : MID SEMESTER exam (25 September 2010 : Saturday) End Semester exam: NOVEMBER 25 (THURS DAY) Tt Tutorial ilis problem solving li class You will be given the Tutorial sheets ONE WEEK in advance You have to come prepared to the class and may be one of you will be asked to 4 solve the problems

5 All Course related material : Syllabus Lecture presentations Problem sheets Solutions will be posted at : 5

6 In case of any need and necessity, we may ask you to come for an extra class On THURS DAY 3 rd Hour (G1 Slot) : Hrs Please Elect TWO representatives from your Batch : PH 1 We all the EIGHT teachers will have periodic meeting with them to Know your problem your concerns your thoughts and opinions on the course. We are here to teach you and help you learn 6

7 What is that t we are going to learn in PH 1010: We will learn : Newtonian Mechanics (You know), Conservative and non conservative forces, conservation of energy, Force and energy methods to solve problems in Physics, Velocity, acceleration and force require direction to be specified hence Vectors, Definition of Cartesian coordinates, right handed coordinate system, Newtonian space, Vector algebra : Vector addition, subtraction, multiplication: Dot and cross products (why there is no vector division?), a few physical examples You feel that t most of the material you already KNOW. Let us see at the end of the semester. 7

8 As you all know: There are only FOUR forces in Nature : Gravitational Electro magnetic Strong Nuclear force Weak Nuclear force If you know how many forces are acting on a body, you can calculate the motion of the body at any given time. But, we encounter forces which we do not know : Frictional force Friction is important for motion (without friction, the body slips or skids) Friction is a NON CONSERVATIVE force. 8

9 What is Conservative e force oce What is a NON CONSERVATIVE Force? How do you define it? Force methods of solving problems in Physics is rather limited. So, what is the next alternative? Energy methods: How many energies are there? Potential and Kinetic What is conservation of energy? Whatis the relation between energy and force? 9

10 If a force is applied to move this table: I am applying the force, but the table is not moving at all Tell me, how much work is done? The earth is moving round the sun : how much work is done? What is the force involved? When an electron is moving round the nucleus, how much work is done? What is the energy involved? Where it comes from? If I move an object in any arbitrary direction i and if I come to the same point as I started, how much work is done? How much energy is spent? You have problems where ACTION AT CONTACT and ACTION AT A DISTANCE (WITHOUT CONTACT) Action at a distance is FIELDS 10

11 Imagine a body is moving under the influence of a force : Say, an electron is moving under the influence of electric and magnetic forces Describe the motion. How are you applying the Electric field + and ve plates How are you applying the magnetic field? N S or S N w.r.t to what DIRECTION is important 11

12 Direction MUST be specified to state your problem. The body can move with uniform velocity or with uniform acceleration How do you describe the motion? How do you express the direction? We can specify the location of the body by THREE Coordinates We specify the Three coordinates in a Frame of Reference or Space If the body moves, we also have to specify TIME Thus SPACE and TIME coordinates locate the body (either stationary tti or in motion) 12

13 If the body is moving with constant acceleration and if the frame of reference also moves with same acceleration, how do you describe the motion? What is an INERTIAL Frame? What is Newtonian space? How many coordinates you require to specify a body? What is a generalized coordinate? (If I wear a Green shirt every day, you can identify me with a Green shirt!!) This is a Generalized coordinate! 13

14 Types of Energy Example: Falling Body Kinetic Energy = 2 m E K mv /2 Potential Energy v E P = mgh Rest Energy h E R = mc 2

15 Classical Physics Picture prior to 20th Century: Energy and matter were separate and distinct i substances. Although appearing continuous to the naked eye, matter was composed of discrete, localized atoms. (Nano Science) Light was a form of electromagnetic wave, the vibration of a continuous cosmic field, the aether, and regarded as a form of "pure energy. " Gravity was a continuous action at a distance field.

16 Modern Physics Current picture: Energy and matter are the same stuff: E = mc 2 The discrete nature of matter is confirmed. Energy is also discrete. Quantum Mechanics There is no evidence for an aether or any other continuous medium in universe. Light is composed of particulate matter: photons. Fields are composed of discrete particles il ("quanta"). ") General relativityexplainsgravityexplains in terms of the curvature of space rather than as a force field.

17 Matter Molecules Atoms Nuclei and Electrons Protons and Neutrons Quarks

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19 The Standard Model of Matter Threegenerations of quarks and leptons u c t d s b e e plus antiparticles. Familiar matter : u, d, e proton = uud neutron = udd

20 Mass of a Proton Proton is made of u u d quarks Mass of proton = Mass of u and d quarks + Kinetic Energy of quarks + Potential Energy between quarks Most of Proton mass comes from energy components! As far as we know, Quark, Lepton and Force carrying Bosons are fundamental Where does their mass comes from?

21 Let us come back to the problem of Forces : 21

22 The Standard Model of Forces Forces result from the exchange of particles: Electromagnetism photon Strong nuclear gluons (8) Weak nuclear weak bosons (4) (No quantum theory of gravity as yet) While these force particles are described by quantum fields in the theory, no continuous medium, like the aether, is involved.

23 The Cosmos Mass Budget Radiation % Odi Ordinary visible iibl matter % Ordinary nonluminous matter 3.5 % Nature of dark matter and dark energy still unknown. But not immaterial since carry mass. Exotic dark matter 26 % Even more exotic dark energy 70 %

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25 So, it is all the same whether we talk of - Forces - Matter - Energy It is only the language of Physics. The Conservation of Energy, Conservation of Matter and Conservation of Charge are of fundamental importance These are the basic laws of Nature These basic laws of Nature can also be Derived from Symmetry. 25

26 Transformations and Invariance Physics should NOT change where ever you observe Transformations Changes from one reference frame to another. Invariance A physics equation is invariant if it does not change under a transformation. y X Covarient : The formula looks the same but meaning of each term is different

27 Symmetries Objects that are invariant under transformations are said to possess symmetry. This object is symmetric in horizontal direction but not the vertical direction.

28 Noether s Theorem For every continuous symmetry of the laws of physics there exists a conservation law and vice versa. -Emmy Noether (1915) Conservation laws follow from point of view Conservation laws follow from point-of-view invariance.

29 Conservation of Linear Momentum F ll f t l ti t Follows from space translation symmetry when there is no special position in space.

30 Breaking Space Translation Symmetry When space translation symmetry is broken, momentum is no longer conserved. We describe the cause as a force.

31 Conservation of Angular Momentum F ll f tti t Follows from space rotation symmetry when there is no special direction in space.

32 Conservation of Energy Follows from time translation symmetry Follows from time translation symmetry when there is no special moment in time.

33 So, the same laws of Physics are told in different languages What ever they talk, they talk of one and the same thing: Forces of Nature Energy principles Formation of Matter Interaction of Matter with Energy All this understanding of Nature is translated into Products : called ENGINEERING. 33

34 Once you know the language, you can understand what is happening Once you know the tools, you can understand your work. These are the tools we teach in this PH 1010 : Language of Physics and Engineering i 34

35 Let us come back to our Newtonian Physics Inertial Reference Frames An inertial reference frame is one in which Newton's laws hold. An accelerating elevator is a non-inertial frame. A reference frame at rest or with constant velocity is an inertial frame. 35

36 Let us fix our frame of reference as INERTIAL Frame Now we describe the motion of a particle under the influence of a force Force must have a direction : The body moving must also have a direction. We can include direction to the Physical observables by VECTORS Before we define the Vector, let us fix our coordinate system. We work with Cartesian co-ordinate system x, y, and z. But remember, to describe the complete motion, we need THREE space coordinates and ONE time coordinate The THREE space co-ordinates must specify the body and its direction of motion un-ambiguously. 36

37 Reference Frame 3 Space + 1 Time are aesufficient ce to describe nature!