College Physics (PHY 1301)

Transcription

1 College Physics (PHY 1301) Lecture 1. Introduction Syllabus and teaching strategy Newtonian Mechanics, Fluid Mechanics and Thermodynamics Physical Quantities, Measurements, Units and Vectors 1 6/1/2015

2 Lecturer: Syllabus and teaching strategy Dr. Sunil Karna, Room 119 Hill Hall, Phone: , Web: Office Hours: MTWR 2:30 AM -5:00 AM, Hill Hall 208 Grading: Homework 15% Regular Tests 60% Final 25% Attendance maximum 3 points (see details of syllabus) Class Rules and Regulations: No electronic devices should be used without instructor permission. It is important for you to come to the class prepared! Homework Sessions: Homework is assigned every week, and due at every Thrusday, Final Exam: There will be THREE (3) Hour Final Exam on 07/02 Thursday at am --- pm. Online Content: Lecture will be made available online to you as a supplemental reference. 2 6/1/2015

3 PHYSICS The word Physics is taken from Greek word Physis meaning Nature. It is the part of science that was developed from Philosophy. It is assumed to be the oldest and basic pure science. Physics is a branch of science that deals with the properties of matter. It is subdivided into two basic parts so called classical physics and modern physics. Chemistry is a branch of science that deals with constituents of matter. Biology is a branch of science that deals with the nature of life.

4 Chapter 1 INTRODUCTION: THE NATURE OF SCIENCE AND PHYSICS Galaxies are as immense as atoms are small. Yet the same laws of physics describe both, and all the rest of nature an indication of the underlying unity in the universe. The laws of physics are surprisingly few in number, implying an underlying simplicity to nature s apparent complexity. The flight formations of migratory birds such as Canada geese are governed by the laws of physics. Science is a systematic study of nature, it consists of empirical, theoretical and practical knowledge of natural world. Supernatural or magical world is beyond its limit till now.

5 Physics, chemistry, and biology help describe the properties of many things surrounds us.

6 Transaction in Daily Life

7 Units Fundamental Units Length [L] Time [T] Mass [M] Foot Meter - Accepted Unit Furlong Second - Accepted Unit Minute Hour Century Kilogram - Accepted Unit Slug 7 6/1/2015

8 Derived Units Single Fundamental Unit Area = Length Length [L] 2 Volume = Length Length Length [L] 3 Combination of Units Velocity = Length / Time [L/T] Acceleration = Length / (Time Time) [L/T 2 ] Jerk = Length / (Time Time Time) [L/T 3 ] Force = Mass Length / (Time Time) [M L/T 2 ] 8 6/1/2015

9 Units SI (Système Internationale) Units: mks: L = meters (m), M = kilograms (kg), T = seconds (s) cgs: L = centimeters (cm), M = grams (g), T = seconds (s) British Units: Inches, feet, miles, pounds, slugs... We will switch back and forth in stating problems. 9 6/1/2015

10 Unit Conversion Useful Conversion Factors: 1 inch = 2.54 cm 1 m = 3.28 ft 1 mile = 5280 ft 1 mile = 1.61 km Example: convert miles per hour to meters per second: mi mi ft 1 m 1 hr hr hr mi 3.28 ft 3600 s m s 10 6/1/2015

11 Orders of Magnitude Physical quantities span an immense range Length size of nucleus ~ m size of universe ~ m Time nuclear vibration ~ s age of universe ~ s Mass electron ~ kg universe ~ kg 11 6/1/2015

12 Physical Scale Orders of Magnitude Set the Scale Atomic Physics ~ m Basketball ~ 10 m Planetary Motion ~ m Knowing the scale lets us guess the Result Q: What is the speed of a boing 747? Distance - New York to LA Flying Time 4000 mi 6 hrs = 660 mph 12 6/1/2015

13 Dimensional Analysis Fundamental Quantities Length - [L] Time - [T] Mass - [M] Derived Quantities Velocity - [L]/[T] Density - [M]/[L] 3 Energy - [M][L] 2 /[T] /1/2015

14 Physical Quantities Must always have dimensions Can only compare quantities with the same dimensions v = v(0) + a t [L]/[T] = [L]/[T] + [L]/[T] 2 [T] Comparing quantities with different dimensions is nonsense v = a t 2 [L]/[T] = [L]/[T] 2 [T] 2 = [L] 14 6/1/2015

15 Units Physics and the Laws of Nature Units of Length, Mass, and Time Dimensional Analysis Significant Figures Converting Units Order-of-Magnitude Calculations Scalars and Vectors Problem Solving in Physics

16 Significant Figures accuracy of measurements is limited significant figures: the number of digits in a quantity that are known with certainty number of significant figures after mathematical operation is the number of significant figures in the least-known quantity

17 Scientific Notation Leading or trailing zeroes can make it hard to determine number of significant figures: 2500, Each of these has two significant figures Scientific notation writes these as a number from 1-10 multiplied by a power of 10, making the number of significant figures much clearer: 2500 = If we write 2.50x10 3, it has three significant figures = 3.6 x 10-5 Round-off error: The last digit in a calculated number may vary depending on how it is calculated, due to rounding off of insignificant digits Example: $ % tax = $2.3868, rounds to $2.39 $ % tax = $1.458, rounds to $1.49 Sum: $ $1.49 = $3.88 $ $1.35 = $3.56 $ % tax = $3.84

18 Converting Units Converting feet to meters: 1 m = ft (this is a conversion factor) Or: 1 = 1 m / ft 316 ft (1 m / ft) = 96.3 m Note that the units cancel properly this is the key to using the conversion factor correctly! Order-of-Magnitude Calculations Why are estimates useful? 1. as a check for a detailed calculation if your answer is very different from your estimate, you ve probably made an error 2. to estimate numbers where a precise calculation cannot be done Scalars and Vectors Scalar a numerical value. May be positive or negative. Examples: temperature, speed, height Vector a quantity with both magnitude and direction. Examples: displacement (e.g., 10 feet north), force, magnetic field

19 Problem Solving in Physics No recipe or plug-and-chug works all the time, but here are some guidelines: 1. Read the problem carefully 2. Sketch the system 3. Visualize the physical process 4. Strategize 5. Identify appropriate equations 6. Solve the equations 7. Check your answer 8. Explore limits and special cases

20 Summary Physics is based on a small number of laws and principles Units of length are meters; of mass, kilograms; and of time, seconds All terms in an equation must have the same dimensions The result of a calculation should have only as many significant figures as the least accurate measurement used in it Convert one unit to another by multiplying by their ratio Order-of-magnitude calculations are designed to be accurate within a power of 10 Scalars are numbers; vectors have both magnitude and direction Problem solving: read, sketch, visualize, strategize, identify equations, solve, check, explore limits