PH 211 Winter 2014

1. PH 211 Winter 2014 Monday January 27

2. Midterm rooms Wednesday 1/29 and 2/19 from 8:30 to 9:50pm Note sheet 8.5 by 11 is OK Chapters 1,2,3, and 4. Format close to 2010. Weniger 151:   A-J Weniger 116:  K-R Weniger 153:  S-Z

3. MP error HW set 3, problem 2.80 part D seems to be wrong. That is a first! I have reported it, and will change scores appropriately.

4. What do you think about multiple choice questions as part of the exam? • Love them • They are OK • Neutral • Don’t care for them • Get rid of them 0 of 208 :36

5. Google moderator Which topic would you like to discuss in class on Wednesday? http://www.google.com/moderator/#16/e=214284

6. Google moderator Which topic would you like to discuss in class on today? http://www.google.com/moderator/#16/e=2108a3

7. Reaction time Mean RT for college-age individuals is approximately 190 milliseconds to detect visual stimulus About 20 folks with responses larger than 1, some as large as 200! Nobody very small, except one zero.

8. Why was the class time faster than the national average? • Data measurement error. Measure D. E.g. distance between lines was not centimeters. Measurement problem. • Error in physical model on which experiment is based. From D to T. E.g. need to include air resistance. Procedural problem in step going from measured data to required data. • Error in experimental set-up. From T to Treac. E.g. the reaction was to another clue. Design problem. • True result. Need to analyze why! Need to be very sure that first three steps are OK.

9. V0=4 m/s The value of X is about 0.7 m 1 m 12 m 28 m 36 m 45 m X m Acceleration of gravity is down.

10. The values of X is about • 0.7 m • 1 m • 12 m • 28 m • 36 m Acceleration of gravity is down. 0 of 209 :01

11. Degrees and radians A radian is a measure of an angle about equal to • 30 degrees • 45 degrees • 60 degrees • 90 degrees • I do not know what you are talking about

12. A radian is a measure of an angle about equal to • 30 degrees • 45 degrees • 60 degrees • 90 degrees • I do not know what you are talking about 0 of 209 1

13. Derivatives

14. Circular motion R

15. Circular motion On a circle of radius r we have s = R θ as long as the angle is measured in radians. R s θ

16. Circular motion The position of a particle on a circle is either given by the distance traveled along the circumference or by the corresponding angle. Angular velocity

17. Uniformcircular motion, v is constant In this case we have • The acceleration is zero • The component of the acceleration parallel to the velocity is zero • The component of the acceleration perpendicular to the velocity is zero • There are in general no non-zero components of the acceleration

18. Uniformcircular motion, v is constant,and we have • The acceleration is zero • The component of the acceleration parallel to the velocity is zero • The component of the acceleration perpendicular to the velocity is zero • There are in general no non-zero components of the acceleration 0 of 209 1

19. Centripetal acceleration In general we have

20. Uniform circular motion,Period T Time to go around once.

21. Earth velocity Radius of earth orbit around sun: RE= 1.5 x 1011 m. What is the velocity of the earth around the sun?

22. Radius of earth orbit around sun: RE= 1.5 x 1011 m.What is the velocity of the earth around the sun? • 3 m/s • 300 m/s • 30,000 m/s • 3,000,000 m/s • 300,000,000 m/s 0 of 209 1

23. Earth velocity Radius of earth orbit around sun: RE= 1.5 x 1011 m. What is the velocity of the earth around the sun? One complete orbit: D = 2 πRE T= 1 year = 365 * 24 * 60 * 60 s v= 2 π 1.5 x 1011 / (365 * 24 * 60 * 60 ) m/s v ≈ 10 x 1011 / ( 400*25*50*50) = 4 x 104 m/s

24. Earth velocity Radius of earth orbit around sun: RE= 1.5 x 1011 m Centripetal acceleration? v ≈ 10 x 1011 / ( 400*25*50*50) = 4 x 104 m/s acent = v2/R ≈ 0.01 m/s2 Is that large or small?