Micro-world Macro-world Fall 2009 Instr: Stephen L. Olsen

1. Micro-world Macro-world Fall 2009 Instr: Stephen L. Olsen

2. What does “Physics” mean? Greek: φίσίσ phisis  Nature “logic” “things” Chinese: 物理 WU LI “The logic of things” or “How things work”

3. What kind of “things”? Ordinary-sized objects:: apples: footballs: etc. ukuleles:

4. Gigantic things Earth galaxies etc. Sun

5. Very tiny things cells molecules atoms quarks

6. Galileo Galilei1562 - 1642 1st “modern” scientist

7. Example of how Galileo thought:His experiments on motion on inclined planes

8. What if the 2nd track was horizontal?

9. Aristotle ~300 BC Forces are needed to keep objects in motion. A constant force will have a constant motion. Physics book VII chapter 5

10. Galileo’s big idea Forces are not needed to keep objects in motion. They are only needed to changethe state of motion.

11. Actually, Galileo wasn’t first If there is no opposing force, motion will never stop. before Aristotle! Mozi ( 墨子 ) ~400BC

12. Object sliding on a surface If there were no friction the book would keep sliding.

13. Angels are not needed to keep planets moving in their orbits

14. Law of inertia Discovered by Galileo, but as written by Newton: Every object perseveres in its state of rest, or of uniform motion in a straight line, unless it is so compelled to change that state of motion by forces impressed thereon.

15. Comment on the Law of Inertia • No mention of balls & tracks • Applies to ordinary objects & also huge objects like galaxies and tiny objects like atoms & quarks Galileo knew nothing of galaxies or quarks, but, thanks to his imagination, his insight, based on observations of ordinary objects, proved to be a universal truth.

16. Units & Reference Frames Required for measurements/observations

17. English units King’s foot 12 inches = 1ft 5280 ft = 1 mile

18. One meter of length 1 meter = 40 inches (1.1 yds) 10,000,000m 1m About the distance from nose to the outstretched finger (of a pretty big guy).

19. Centimeters & millimeters 1 centimeter = 1/100 meters ( radius of a penny) 1cm 1 millimeter = 1/1000 meters ( thickness of a dime) 1mm means “approximately equal to”

20. 1000 m = 1 kilometer (km) 1km  5/8 mile

21. Motion depends on the circumstances of the observer (I) backward forward • To us, both the red & blue cars move forward • To someone in the red car, the blue car is going backwards

22. Reference frames akaCoordinate systems z-axis (vertical) To describe the position of an object: You need to define a coordinate system (reference frame) & determine 3 coordinates e.g. x, y & z z reference point (e.g. home plate) z y-axis (e.g. the 3rd baseline) y x Choices of location of the coordinate system & directions of the axes are up the observer. x-axis (e.g. the 1st baseline)

23. Motion depends on the circumstances of the observer (II) z y x • In the fish’s reference frame, it is the ground that is moving

24. Some distances Nose to finger ~1m Back of the room ~10m SNU library ~100m SNU main gate ~1000m Incheon ~50000m Center of the Earth ~6400000m Earth to Moon ~385000000m Earth to Sun ~150000000000m Next star ~40000000000000000m We are only out to the next star & we are already running out of space

25. Some small sizes • radius of a 10 won coin ~0.01 m • thickness of a 10 won coin ~0.001 m • thickness of a human hair ~0.000075 m • diameter of a red blood cell ~0.00000002 m • size of hydrogen atom ~0.00000000006 m • size of hydrogen nucleus ~0.0000000000000001 m Again, the numbers become unwieldy & use up a lot of space

26. Exponential logic

27. Exponential logic powers of “2”

28. Area of a sheet of paper 21.5 cm Area =28 cm x 21.5 cm = 600 cm2 28 cm Cut it in half

29. Area of the remaining sheet after 1 cut Area =28 cm x 21.5 cm 2 21.5 cm = 600 cm2 2 = 600 (1/2)cm2 28 cm 2 =300 cm 2 Cut it in half again

30. Area of the remaining sheet after 2 cuts Area =28 cm x 21.5 cm 21.5 cm 2 2 2 = 600 cm2 2x2 28 cm =600 cm 2 x(1/2)2 2 =150cm2 Cut it in half again

31. Area of the remaining sheet after 3 cuts Area =28 cm x 21.5 cm 21.5 cm 2x2 2 2 = 600 cm2 2x2x2 =600 cm 2 x(1/2)3 1 2 28 cm 2 =75cm2 Cut it in half again

32. After 12 times Area =28 cm x 21.5 cm 21.5 cm 26 26 26 28 cm = 600 cm2 26 26x26 =600 cm 2 x(1/2)12 = 600 cm2 4096 =0.15 cm2 Smallest piece of paper I can handle

33. Imagine we did it 70 times 21.5 cm Area =28 cm x 21.5 cm 235 235 235 28 cm = 600 cm2 235 235x235 =600 cm 2 x(1/2)70 1 =600 cm2 x 1,180,591,620,717,411,3??,??? = 5.1 x10-19 cm2 (about ½ the area of an atom)

34. 1 1,180,591,620,717,411,3??,??? is unwieldy (다루기 힘든, 꼴 사나운) Difficult to manage (1/2)70 Is more tractable Tractable easy to manage

35. Powers of 10 $100.0 = $10.00 x 10 Move the decimal point 1 place to the left multiply by 10 & “penny” “dime” $0.01 = $00.1 x 1/10 Move the decimal point 1 place to the right divide by 10 &

36. Positive powers of 10 1500000.00000 x 105 150000000000 150000000000. 15000000000.0 x 101 1500000000.00 x 102 150000000.000 x 103 15000000.0000 x 104 15000.0000000 x 107 1500.00000000 x 108 150.0000000000 x 109 15.0000000000 x 1010 1.50000000000 x 1011 1500000000.00 x 10x10 150000.000000 x 106 11 jumps to the left  +11 in the exponent = 1.5 x 1011

37. Some distances • Nose to finger ~1 m • The back of the room ~10 m • SNU Library ~100 m • SNU Main gate ~1000 m • Incheon ~50000 m • Center of Earth ~6400000 m • Earth to Moon ~386,000,000 m • Earth to Sun ~150000000000 m • Next star ~40000000000000000 m ~5.0 x 104 m ~6.4 x 106 m ~3.86 x 108 m ~1.5 x 1011 m ~4.0 x 1016 m

38. nomenclature • 103 = 1 thousand (kilo) • 106 = 1 million (mega) • 109 = 1 billion (giga) • 1012 = 1 trillion (tera)

39. Small numbers 1 penny = $0.01 1 dime= $0.10 1 penny = 1/10th of a dime $0.01 = $0.10x(1 /10) Moving the decimal point 1 place to the right is the same as multiplying by 10

40. Negative powers of 10 00000.0000006 x 10-4 0.00000000006 00.0000000006 x 1/10 00.0000000006 x 10-1 000.000000006 x 10-1x10-1 000.000000006 x 10-2 0000.00000006 x 10-3 0000000.00006 x 10-6 00000000.0006 x 10-7 000000000.006 x 10-8 0000000000.06 x 10-9 00000000000.6 x 10-10 000000000006.x 10-11 000000.000006 x 10-5 11 jumps to the right  -11 in the exponent = 6.0 x 10-11

41. Some small sizes • radius of a 10 won coin ~0.01 m • thickness of a 10 won coin ~0.001 m • thickness of a human hair ~0.000075 m • diameter of a red blood cell ~0.00000002 m • size of hydrogen atom ~0.00000000006 m • size of hydrogen nucleus ~0.000000000000001 m ~7.5 x 10-5 m ~2.0 x 10-8 m ~6.0 x 10-11 m ~1.0 x 10-15 m

42. More nomenclature • 10-2 = centi- • 10-3 = milli- • 10-6 = micro- (m) • 10-9 = nano- • 10-12 = pico-

43. exponents are very important Distance to the Sun: 1.5 x 1011m Distance to next star: 4 x 1016 m 8 minutes from now Light from the sun takes 8 minutes to get here Exponents differ by 5 Light from the next star takes 4 years to get here 4 years from now?

44. Multiplying large numbers 10a+b Use the rule: (A x 10a ) x (B x 10b) =(AxB) x (10a x 10b) Number of people In the US x average income/person on 1/8/07 301,000,000 x $ 40,100 = 3.01x108 x $ 4.01x104 = (3.01 x $4.01) x (108 x 104) = $1.21 x 1013 = $12.1 x 108+4 =$12.1 x 1012 Sum of everyone’s income

45. dividing large numbers 10a-b A B 10a10b A B Ax10a x 10a x 10-b = x = Bx10b & change sign move b upstairs $8,598,000,000,000 301,000,000 persons on 818/07 US national debt # of persons in US = $8.60 x 1012 3.01 x 108persons $8.60 1012 3.01 108persons x = = = $2.86 x 1012- 8 /person = $2.86 x 104/person (= $28,600/person)

46. $28,600 (ladies not included)