Reading Quiz. How many years of physics have you had?

Transcription

1 Reading Quiz How many years of physics have you had? 1) None 2) One 3) Two or more

2 Physics nl8n/201/ PHYS 201 homepage.htm Go to Toolkit under Materials after every lecture to look at the notes. All course information is on the above Website Let s go through some things

3 What you need for the course Textbook: Physics, 3rd Edition by Walker Optional: Student Study Guide and Selected Solutions Manual; Mastering Physics

4 iclicker: Important to understand the policy for using this unit

5 Course Objectives: To learn and understand the physical world How? Problem Solving and Conceptual Understanding

6 Lectures Quiz and Conceptual Questions Homeworks Discussion Section Quizzes

7 WebAssign Homeworks will be found and submitted on WebAssign. Look at the Website for more information. You have been sent your WebAssign logon information. Try it!

8 My office hours and those of the TA s can be found on the class Web page

9 Final grades Final Exam 40% Two hour-exams 40% Homework 15% Problem Session Quizzes 4% Quizzes in Lectures 1%

10 Behavior to avoid in class Reading the newspaper (or comics books) Surf the Web Private chats

11 Entering and leaving class at inappropriate times Loud snoring Having nightmares while snoring

12 How to learn from the Textbook Work out the conceptual questions at the end of each chapter. Work out extra problems (call beyond duty).

13 The Student Study Guide (optional) is very useful. Learn the strategy of problem solving from Problem-Solving Summaries.

14 Units of Length, Mass and Time Length: meter (m) One ten-millionth of the distance between the North Pole and the Equator, two marks on a platinum-iridium rod in Paris (where else?).

15 Distance traveled by light in vacuum in 1/299,792,458 of a second 1 inch = 2.54 cm; 3.28 ft = 1 m Mass: kilogram (kg) Kilogram = mass of platinumiridium cylinder kept outside Paris

16 Mass (intrinsic property) Weight (force due to gravity) Time: second (s) Earth rotation, etc... Most accurate: Atomic Clock (Cesium-133) Those are called SI units. Typical distances: Table 1-1.

17 Typical masses: Table 1-2 Typical times: Table 1-3 Multiples of basic units are common regardless of the system used. Common prefixes are shown in Table 1-4. One last comment:keep your units straight!

18 Dimensional Analysis Apples Oranges Example: x = x 0 + vt x: distance [L] v: velocity (distance/time) [L]/[T]

19 [L] = [L] + ([L]/[T])[T] OK! x = x 0 + vt 2 Not OK!

20 Significant Figures Very Important! Significant Figure = Number of digits known with certainty Ex.: x = 2.5m x is known to two significant figures.

21 Multiplication or Division: a b = c or a/b = c. number of sig fig for c = number of sig fig of the least accurate of a or b Same for more complicated manipulations Addition or Subtraction: a + b = c or a b = c. number of decimal places for c =

22 number of decimal places of the least accurate of a or b Same for more complicated manipulations Remember to keep all significant figures in your calculations until the very end, especially in WebAssign! Do not round off the numbers until you reach the end

23 Example The Coyote steadily sneaks upon the Roadrunner with a constant speed of 1.2 m/s. How much distance has he covered after 5.35 s? 1) 1.2m/s 5.4s = 6.48m 2) 1.2m/s 5.4s = 6.5m

24 3) 1.2m/s 5.35s = 6.42m 6.4m ** For (1): Incorrect number of Sig Fig in the answer; Round-off error in the time For (2): Correct number of Sig Fig in the answer but round-off error in the time For (3): Everything is done correctly

25 Exception: In WebAssign problems, you must get within 1% of the correct answer. Keep all sig fig in calculations and express answers to 3-4 sig figs.

26 Scientific Notation Example: Speed of Light = 299, 792, 458 m/s In this way, it is known to 9 sig figs It can be written as m/s

27 One can write it as m/s if it is known to 2 sig figs

28 How do we change from one unit to Example: Kareem Abdul-Jabar is 7-foot-2. How tall is he in meters? Answer: 1) 2 in = 1/6 ft; 2) 7 foot ft = 7.16ft/3.28ft = 2.18m

29 Order-of-magnitude estimates How many grains of rice are there in the jar lying on that table in class?

30 Problem Solving Read the problem carefully Sketch the system Visualize the physical process Find a strategy

31 Find the appropriate equations Solve the equations Check your answer Limits and special cases

32 Chapter 2 One-dimensional: along a line Kinematics: Study and description of motion regardless of the cause Position: With respect to what? Choose a coordinate system

33 Example: Fig. 2-1 Distance: Total length traveled Displacement: change in position = final position - initial position Displacement = x = x f x i

34 Example Fig. 2-3 What is the distance traveled after 4 s? 1) -2 m

35 2) 5 m 3) 8 m

36 Answer: 8 m What is its displacement? 1) 3 m 2) -2 m 3) -4 m

37 Answer: -2 m

38 Average Speed and Velocity Average speed = distance/elapsed time Average velocity = displacement/elap time Example: Fig. 2-3

39 What are the average speed and average velocity after 3 s starting from t = 0 s?

40 Answers: 1) average speed = 5/3m/s 1.7m/s 2) average velocity = (2m 1m)/3s = 1/3m/s 0.3m/s Fig. 2-4 and 2-5 show x-versus-t and showing graphically the average velocity