1. SMDEP Physics Work, Power, Potential Energy

2. New Syllabus Available at front Shifting topics by one day through “gravity”; one day less on gravity –NO HOMEWORK FOR WEDS! –Also, no TA session Weds Andrew teaching WTh, MTu –KR available by email Quiz on Friday

3. Friday’s Mechanics Quiz No calculators needed/allowed No clickers needed Don’t memorize formulas –Any formulas needed will be provided Mostly qualitative, conceptual questions Length: About 30 minutes Material: Kinematics, Mechanics, Energy –Circular motion, friction, springs –NOT: vectors, dot products, momentum Grades not instant Also: Midcourse evaluations –What would you change about the course?

4. Resources Textbook: especially end-of-chapter “Questions” New web site –http://www.astro.yale.edu/krines/smdep/ –Powerpoints of first two weeks, more to come Email –KR: krines@astro.yale.edu –AC: andrew.cahoon@yale.edu Office hours: KR today 5-6 pm Marigolds

5. Ch 8, #1: distance spring stretched 1.0.09 m 2.0.9 m 3.9 m 4.90 m 5.Other 6.Didn’t finish

6. Ch 8, #8: is air resistance conservative? 1.Yes 2.No 3.Sometimes 4.Didn’t finish

7. Normal forces –Always act at right angles to surface –Force of electron clouds repelling each other –Friction always normal to normal force, so friction is always parallel to surface “Centrifugal forces” – NO! “The centripetal force” – No “A centripetal force” – Yes –Centripetal force is always exerted by something touching object or gravity: e.g., normal force from rollercoaster track, string/rope tension force, Earth’s gravity

8. A stone is attached to a string is whirled in a vertical plane. Let T1, T2, T3, and T4 be the tensions required (at the locations shown) for the stone to have a constant speed v0 throughout. Which is true? T1T1 T4T4 T2T2 T3T3 1.T 3 > T 2 > T 1 = T 4 2.T 3 = T 2 = T 1 = T 4 3.T 1 > T 2 = T 4 > T 3 4.None of the above

9. You are pushing a wooden crate across the floor at constant speed. You then turn the crate on end, reducing by half the surface area touching the floor. In the new orientation, to push the same crate across the same floor with the same speed, the force that you apply must be about: 1.Four times greater 2.Twice as great 3.Equally great 4.Half as great 5.One-fourth as great

10. Consider a person standing in an elevator that is accelerating upward. The upward normal force exerted by the elevator floor on the person is: 1.Larger than 2.Equal to 3.Smaller than..the downward weight of the person

11. You stand on a scale in your bathroom. It reads 150 lb. In which of the following situations will it read less? 1.In an elevator accelerating upward 2.In an elevator accelerating downward 3.In an elevator moving up at constant velocity 4.In an elevator moving down at constant velocity 5.Two of the above

12. In the 17th century, Otto von Güricke, a physicist in Magdeburg, fitted two hollow bronze hemispheres together and removed the air from the resulting sphere with a pump. Two eight-horse teams could not pull the halves apart even though the hemispheres fell apart when air was re-admitted. Suppose von Güricke had tied both teams of horses to one side and bolted the other side to a heavy tree trunk. In this case, the tension on the hemispheres would be: 0 70 10 1.Twice 2.The same as 3.Half..what it was before

13. Consider a weightlifter holding a 500 pound barbell stationary above his head. The weightlifter is doing: 1.Positive work on the barbell 2.Negative work on the barbell 3.No work on the barbell