advertisement

ANNOUNCEMENTS •Students that have purchased a book that includes the access code to WileyPlus, can submit the homework in WileyPlus INSTEAD of WebAssign. •All students must go once a week to recitation (R 300) and once a week to Lab (R 305). See the syllabus to know which day you have lab or rec. or check with your instructor. •The first homework is posted in WebAssign and WileyPlus. Deadline is extended until Sep. 4 to allow all students to register in the system. •If you have questions please ask me after the lecture. Chapter 1 Introduction and Mathematical Concepts 1.2 Units SI units meter (m): unit of length kilogram (kg): unit of mass second (s): unit of time 1.2 Units 1.3 The Role of Units in Problem Solving 1.2 Units The units for length, mass, and time (as well as a few others), are regarded as base SI units. These units are used in combination to define additional units for other important physical quantities such as force and energy. 1.3 The Role of Units in Problem Solving THE CONVERSION OF UNITS 1 ft = 0.3048 m 1 mi = 1.609 km 1 hp = 746 W 1 liter = 10-3 m3 1.3 The Role of Units in Problem Solving Example 1 The World’s Highest Waterfall The highest waterfall in the world is Angel Falls in Venezuela, with a total drop of 979.0 m. Express this drop in feet. Since 3.281 feet = 1 meter, Length = 979.0 (meters) = 979.0 (3.281 feet) = 3212 feet 1.3 The Role of Units in Problem Solving Reasoning Strategy: Converting Between Units 1. In all calculations, write down the units explicitly. 2. Treat all units as algebraic quantities. When identical units are divided, they are eliminated algebraically. 3. Use the conversion factors located on the page facing the inside cover. 1.3 The Role of Units in Problem Solving Example 2 Interstate Speed Limit Express the speed limit of 65 miles/hour in terms of meters/second. Use 5280 feet = 1 mile and 3600 seconds = 1 hour and 3.281 feet = 1 meter. miles 5280 feet feet Speed 65 65 95 hour 3600 s second feet (1/3.281) meter meters Speed 95 95 29 second second second 1.3 The Role of Units in Problem Solving DIMENSIONAL ANALYSIS [L] = length [M] = mass [T] = time Is the following equation dimensionally correct? x vt 1 2 2 L 2 L T LT T Wrong 1.3 The Role of Units in Problem Solving Is the following equation dimensionally correct? x vt L L T L T Right 1.4 Trigonometry: Review 1.4 Trigonometry ho sin h ha cos h ho tan ha 1.4 Example: how high is the building? ho tan ha ho tan 50 67.2m ho tan 50 67.2m 80.0m 1.4 Trigonometry ho sin h 1 ha cos h 1 ho tan ha 1 1.4 Example: How deep is the lake? ho tan ha 1 2.25m tan 9.13 14.0m 1 d 22.0m tan(9.13 ) 3.53 o 1.4 Trigonometry Pythagorean theorem: h h h 2 2 o 2 a 1.5 Scalars and Vectors A scalar quantity is one that can be described by a single number: temperature, speed, mass A vector quantity deals inherently with both magnitude and direction: velocity, force, displacement 1.5 Scalars and Vectors Arrows are used to represent vectors. The direction of the arrow gives the direction of the vector. The length of a vector arrow is proportional to the magnitude of the vector. 8 lb 4 lb 1.6 Vector Addition (Graphical) Example: Car moves on two steps, both due East 1.6 Vector Addition (Graphical) 3m 5m 8m Example: Car moves on two steps, first due east, later due north. 2.00 m 6.00 m 1.6 Vector Addition (Graphical) R 2.00 m 6.00 m 2 R 2 2 2.00 m 6.00 m 2 2 6.32m R 2.00 m 6.00 m 1.6 Vector Addition (Graphical) tan 2.00 6.00 tan 1 2.00 6.00 18.4 6.32 m 2.00 m 6.00 m 1.6 Vector Addition (Graphical) When a vector is multiplied by -1, the magnitude of the vector remains the same, but the direction of the vector is reversed. 1.6 Vector Addition (Graphical) B AB A A AB B 1.7 The Components of a Vector x and y are called the x vector component and the y vector component of r. 1.7 The Components of a Vector The vector components of A are two perpendicu lar vectors A x and A y that are parallel to the x and y axes, and add together vectoriall y so that A A x A y . 1.7 The Components of a Vector It is often easier to work with the scalar components rather than the vector components. Ax and Ay are the scalar components of A. xˆ and yˆ are unit vecto rs with magnitude 1. A Ax xˆ Ay yˆ 1.7 The Components of a Vector Example A displacement vector has a magnitude of 175 m and points at an angle of 50.0 degrees relative to the x axis. Find the x and y components of this vector. sin y r y rsin 175 msin 50.0o134 m cos x r x rcos 175 mcos50.0o112 m r r 112 mxˆ 134 myˆ 1.8 Addition of Vectors by Means of Components C AB A Ax xˆ Ay yˆ B Bx xˆ By yˆ 1.8 Addition of Vectors by Means of Components r C Ax xˆ Ay yˆ Bx xˆ By yˆ Ax Bx xˆ Ay By yˆ Cx Ax Bx C y Ay By