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Dr. Mazen Alrahili مازن الرحيلي.د E-mail: [email protected] HOURS : LECTURES, TUTORIALS, OFFICE OHURS 2 Textbook The required textbook is compiled from books published by Pearson...
Dr. Mazen Alrahili مازن الرحيلي.د E-mail: [email protected] HOURS : LECTURES, TUTORIALS, OFFICE OHURS 2 Textbook The required textbook is compiled from books published by Pearson: Introduction to Physics (2014) Compiled by: Prof. Osama A. Yassin, Dr. Mahdi Yousif, Dr. Bilel Zarour , Prof. Isam Salih, Dr. Azza Moharram Course Contents 1. Introduction to Physics, Units and Measurements 2. Mechanics 3. Heat and Properties of Matter 4. Electricity 5. Light and Optics 6. Modern Physics NO measurement is absolutely precise ضبط OR accurate دقَة Good accuracy Poor accuracy Poor accuracy Good precision Good precision Poor precision Precision refers to the repeatability of a measurement using a given instrument. Accuracy refers to how close a measurement is to the true value Main sources of uncertainty شىء مشكوك فيه,(مجهولerrors): Human errors: Limited Instrument accuracy (systematic error) Relatively accurate ruler with least reading ~ 0.05 unit Less accurate ruler. Its least reading ~ 0.5 unit Smallest division = 1 mm = 0.1 cm The ruler is precise to within 0.1 cm, estimated uncertainty (error) = 0.1 cm The tiny book is 3.7 0.1 cm wide Width of thumbnail = 1.3 0.1 cm its true width likely lies between 3.8 and 3.6 cm it lies between 1.4 and 1.2 cm Therefore measurement result is expressed as: (Result Error) unit Measurement result is expressed as: (Result Error) unit Error The percent uncertainty = 100 % Result Example: Error The Percent U ncertainty (P.U.) = 100 % Result Error = 0.4 cm ; result = 20.2 cm 0.4 cm P.U. = 100 % = 1.9801 % 2 % 20.2 cm Example: Result = 2.03 m2 (with two decimal places) In this case the error is taken as the smallest number with two decimal places. Error = 0.01 m2 Error The Percent U ncertainty (P.U.) = 100 % Result 0.01 m 2 P.U. = 2 100 % 0.5 % 2.03 m Significant figure The number of reliably known digits in a number For example: 2 cm, 2.0 cm, & 2.00 cm are mathematically the same but experimentally different: They have different significant figures. Counting rules Rule 1: All nonzero digits (1, 2, 3, …, 7, 8, 9) are significant figures Q. determine the number of significant figures in: 11 and 235.68 Ans. 1 1 Has two significant figures 2 3 5. 6 8 Has five significant figures Rule 2: Zeros Trailing تَ َخلُّفzeros (to Zeros in-between Leading zeros (to the the right of a number) digits left of a number) Count Don’t count 2 0 33 0 0 91 1 0 01 0.1 Number with Number without decimal point decimal point 01 0 6. 2 2 0. 0 0 51 Count Don’t count 10.0 0 10 6 30. 630 17.3 0 0 540000 Check your understanding Significant figure: mathematical operations Carry out intermediate calculations without rounding. Only round the final answer (outcome) according to the following rules: 1. Multiplications and divisions Final result presented with significant figures similar to that for the number with least significant figure used in the operation. Round 11.3 cm 2. 0 cm = 22.6 cm2 ⎯⎯⎯⎯→ 2 3 cm2 See page 6 in your book for more details 2. Addition and subtraction Final result presented with decimal places similar to that for the number with least decimal places used in the operation. Round 9.300 cm + 0. 01 cm = 9.310 cm ⎯⎯⎯⎯→ 9. 31 cm Check your understanding Powers of 10 (Scientific Notation )الترقيم العلمي Common to express very large or very small numbers using powers of 10 notation. Examples: 39,600 = 3.96 104 (moved decimal 4 places to left) 0.0021 = 2.1 10-3 (moved decimal 3 places to right) Useful for controlling significant figures: 39600 3.9 6 0 104 = 3.9 6 0 0 0 0 104 4 104 Units, Standards, SI System All measured physical quantities have units. Units are VITAL مهم للغايةin physics!! The SI system of units: SI = “Systéme International” (French) More commonly called the “MKS system” (meter-kilogram-second) or more simply, “the metric system” SI or MKS System Defined in terms of standards (a standard one unit of a physical quantity) for length, mass, time, …. Length unit: Meter (m) (kilometer = km = 1000 m) – Standard meter. Newest definition in terms of speed of light Length of path traveled by light in vacuum in (1/299,792,458) of a second! Time unit: Second (s) – Standard second. Newest definition time required for 9,192,631,770 oscillations of radiation emitted by cesium atoms! – An earlier definition is terms of the solar day: (1 sec = 1/86400 of the solar day) Mass unit: Kilogram (kg) (kilogram = kg = 1000 g) – Standard kg. A particular platinum-iridium cylinder whose mass is defined as exactly 1 kg SI Base Quantities and Units 1. 2. 3. 4. 5. 6. 7. SI Derived Quantities and Units All physical quantities are defined in terms of the base quantities Example: Derived units for speed, acceleration and force: Distance (m) velocity (m/s) Speed (m/s) = Accelerati on (m/s 2 ) = Time (s) Time (s) Force (Newton, N) = Mass (kg) Accelerati on (m/s 2 ) Larger & smaller units defined from SI standards by powers of 10 & Greek prefixes البادئات Fullerene molecule 10000 km 1 dm (10 m) 7 (10 m ) -1 1 nm (10 m ) -9 Other Systems of Units CGS (centimeter-gram-second) system – Centimeter = 0.01 meter – Gram = 0.001 kilogram British (foot-pound-second) system – Our “everyday life” system of units – Still used in some countries like USA Suppose you are to convert 15 US Dollar ($) into Saudi Ryal (SR) : 1st Find conversion factor: 1 $ = 3.75 SR 2nd 1$ = 3.75 SR 1 = 3.75 SR 1$ 1$ $ SR 3rd 15 $ = 15 $ 1 = 15 $ 3.75 = 56.25 SR $ Likewise convert 21.5 inches (in) into cm : 1st Conversion factor: 1 in = 2.54 cm 2nd 1in 2.54 cm cm = 1 = 2.54 1in 1in in cm 3rd 21.5 in = 21.5 in 1 = 21.5 in 2.54 = 54.6 cm in Hint: 1 ft = 12 in and 1 in = 2.54 cm Hint: 1 m3 = 1000 L. Order of Magnitude; Rapid Estimating Sometimes, we are interested in only an approximate value for a quantity. We are interested in obtaining rough or order of magnitude estimates. Order of magnitude estimates: Made by rounding off all numbers in a calculation to 1 significant figure, along with power of 10. – Can be accurate to within a factor of 10 (often better) The dimension of a physical quantity is the type of units or base quantities that make it up. Base quantity Dimension abbreviation Length [L] Time [T] Mass [M] … … [L] Dimension of the velocity & speed = [ V ] = [T] [L] Dimension of the acceleration = [ T2 ] Dimensional analysis: Example: V = V + a t2 Final velocity Initial velocity acceleration time Left Hand Side (LHS) Right Hand Side (RHS) [ L] ? [ L] [ L] [ L] = + 2 [T ] = 2 + [ L] [T ] [T ] [T ] [T ] LHS dimension RHS dimension RHS dimension LHS dimension RHS dimension The equation is incorrect If LHS dimension = RHS dimension The equation is dimensionally correct (But could be physically incorrect) Ex. Which of the following is dimensionally correct Where g is the acceleration due to gravity Assessment Question 1 The new definition of the SI unit of length is: A. one ten millionth of the distance from the north pole to the equator B. the distance that light travels in a vacuum in a precise time C. the length of a platinum-iridium alloy bar kept in Paris D. 3.280 feet. Question 2 The SI base unit of time is: A. second B. minute C. hour D. day Question 3 State which of the following is the SI base unit of volume. A. Cubic cm (cm3) B. Millilitre (ml) C. Cubic meter (m3) D. Cubic foot (ft3) Question 4 Convert 0.75 cm3 to mm3. A. 7500 mm3 B. 7.5 mm3 C. 75 mm3 D. 750 mm3 Question 5 A mile is 5280 feet. What is 1 kilometer in miles to two significant figures? (Use the conversion factor 1 m = 3.28 ft.) A. 1.6 miles B. 0.62 miles C. 0.062 miles D. 0.621 miles Question 6 An order of magnitude estimate is likely to be accurate within a factor of: A. 100 B. 5 C. 10 D. 2 Question 7 Make an order of magnitude estimate of 3.14 27,800. A. 9 104 B. 9 105 C. 6 104 D. 9 103 Question 8 A swimming pool is 25 m long, 10 m wide and the depth varies from 1 m in the shallow end to 2 m at the deep end. Assuming the density of water is 1 g/cm3, what is the best estimate of the mass of water in the pool? A. 4 103 kg B. 4 104 kg C. 4 106 kg D. 4 105 kg Question 9 What are the dimensions of velocity? A. [L/T] B. [L/T2] C. [M] D. [M/T] Question 10 The dimensions of density are [M/L3]. Which of these would not be a valid unit for measuring density? A. g/cm3 B. kg/m2 C. kg/m3 D. g/m3 Question 11 Atmospheric pressure is 1.01 105 N/m2 (newtons per meter squared). Newton is the SI unit of force. What are the dimensions of pressure? A. [M/LT2] B. [ML/T2] C. [M/LT] D. [ML/T] END OF CHAPTER ONE
