Modern Physics. Light and Relativity

Transcription

1 Modern Physics Light and Relativity

2 Electromagnetism In the late 1800 s, Electricity and Magnetism were united as one force: Electromagnetism

3 Electromagnetism In the late 1800 s, Electricity and Magnetism were united as one force: Electromagnetism With a moving electric field: we get a magnetic field

4 Electromagnetism In the late 1800 s, Electricity and Magnetism were united as one force: Electromagnetism With a moving electric field: we get a magnetic field With a moving magnetic field: we get an electric field

5 Electromagnetism In the late 1800 s, Electricity and Magnetism were united as one force: Electromagnetism With a moving electric field: we get a magnetic field With a moving magnetic field: we get an electric field Two forces move relative to each other at: the speed of light!

6 Electromagnetism In the late 1800 s, Electricity and Magnetism were united as one force: Electromagnetism With a moving electric field: we get a magnetic field With a moving magnetic field: we get an electric field Two forces move relative to each other at: the speed of light! 3x10 8 m/s (300,000,000 m/s)

7 Light Light is an electromagnetic wave, made up of a photon.

8 Light Light is an electromagnetic wave, made up of a photon.

9 Light There started to be some issues with physics around 1880

10 Relative Motion Motion must be measured from some point!

11 Relative Motion Motion must be measured from some point! Who is moving relative to who?

12 Relative Motion Motion must be measured from some point! Who is moving relative to who? George

13 Relative Motion

14 Relative Motion

15 Relative Motion Gracie

16 Relative Motion

17 Relative Motion

18 George, floating in space at a constant velocity, saw Gracie simply float by him Relative Motion

19 George, floating in space at a constant velocity, saw Gracie simply float by him Relative Motion Gracie, floating in space at a constant velocity, saw George simply float by her

20 George, floating in space at a constant velocity, saw Gracie simply float by him Relative Motion WHO S RIGHT? Gracie, floating in space at a constant velocity, saw George simply float by her

21 They both are right! Relative Motion

22 They both are right! Relative Motion You simply have to describe where motion is occurring!

23 Relativity Relativity Rules 1) All Physics are the same in all reference frames

24 Relativity

25 Relativity 30 m/s

26 Relativity 30 m/s

27 Relativity 10 m/s 30 m/s

28 Relativity Relative to George the Cheetah runs 30 m/s

29 Relativity Relative to George the cheetah runs 30 m/s Relative to Usain Bolt, the cheetah runs 20 m/s

30 Relativity 10 m/s

31 Relativity 10 m/s

32 Relativity 10 m/s 300,000,000 m/s

33 Relativity Relative to George the photon travels at the speed of light

34 Relativity Relative to George the photon travels at the speed of light Relative to Usain Bolt the photon travels the speed of light minus 10 m/s?

35 Relativity Relativity Rules 1) All Physics are the same in all reference frames 2) The speed of light is observed to be constant in all reference frames

36 Relativity Relative to George the photon travels at the speed of light Relative to Usain Bolt the photon travels the speed of light minus 10 m/s? HOGWASH!!! The speed of light is constant in all frames!

37 Relativity Relative to George the photon travels at the speed of light Relative to Usain Bolt the photon travels at the speed of light

38 Relativity 10 m/s 300,000,000 m/s

39 Relativity 10 m/s How can the photon be seen as going the same velocity to both people? 300,000,000 m/s

40 Relativity 10 m/s How can the photon be seen as going the same velocity to both people? 300,000,000 m/s

41 Time Dilation Let s look at the most simple, but impractical, clock

42 Time Dilation Let s look at the most simple, but impractical, clock Photon Clock

43 Time Dilation Let s look at the most simple, but impractical, clock Photon Clock

44 Time Dilation Let s put the Photon Clock on racecar!

45 Time Dilation Let s put the Photon Clock on racecar! From the driver s perspective, the photon only travels up and down

46 Time Dilation Let s put the Photon Clock on racecar! From the driver s perspective, the photon only travels up and down

47 Time Dilation Let s put the Photon Clock on racecar! From a spectator s perspective, we see much different motion

48 Time Dilation Let s put the Photon Clock on racecar! From a spectator s perspective, we see much different motion

49 Time Dilation Let s put the Photon Clock on racecar! From a spectator s perspective, we see much different motion The spectator see s the photon take a longer time to complete one cycle because it traveled farther!

50 Time Dilation Let s put the Photon Clock on racecar! From a spectator s perspective, we see much different motion The spectator see s the photon take a longer time to complete one cycle because it traveled farther!

51 Time Dilation Time appears to move at a slower rate for someone who is in motion!

52 Time Dilation Time appears to move at a slower rate for someone who is in motion! For the stationary person, time is dilated when compared to the person in motion

53 Time Dilation Time appears to move at a slower rate for someone who is in motion! For the stationary person, time is dilated when compared to the person in motion If I travel at the speed of light, time doesn t even progress!

54 Twin Paradox One twin journeys on a spaceship at speeds near the speed of light. Since time travels slower for the twin on the spaceship, when they come back from the journey they appear to be younger than their twin

55 Twin Paradox One twin journeys on a spaceship at speeds near the speed of light. Since time travels slower for the twin on the spaceship, when they come back from the journey they appear to be younger than their twin

56 Length Contraction Let s put the Photon Clock on racecar! From the driver s perspective, the photon only travels up and down

57 Length Contraction Let s put the Photon Clock on racecar! From the driver s perspective, the photon only travels up and down

58 Length Contraction Let s put the Photon Clock on racecar! From the driver s perspective, the photon only travels up and down

59 Length Contraction Let s put the Photon Clock on racecar! From the driver s perspective, the photon only travels up and down The photon doesn t travel as far as compared to the spectator!

60 Length Contraction Length appears to be shortened while someone is in motion. For the person in the racecar, lengths are all contracted (meaning shorter).

61 Relativistic Mass As you approach the speed of light

62 Relativistic Mass As you approach the speed of light: your mass will increase

63 Relativistic Mass As you approach the speed of light: your mass will increase E = mc 2

64 Relativistic Mass As you approach the speed of light: your mass will increase E = (Δm)c 2

65 Relativistic Mass As you approach the speed of light: your mass will increase E = (Δm)c 2 So as I go faster, it takes more energy to go faster. If I go the speed of light, it takes an INFINITE amount of energy to do so!

66 Relativistic Mass As you approach the speed of light: your mass will increase E = (Δm)c 2 So as I go faster, it takes more energy to go faster. If I go the speed of light, it takes an INFINITE amount of energy to do so! Relativity tells us that mass and energy are the same!

67 Modern Physics Light and Relativity Review

68 Relativity Relativity Rules 1) All Physics are the same in all reference frames

69 Relativity Relativity Rules 1) All Physics are the same in all reference frames 2) The speed of light is observed to be constant in all reference frames

70 Relativity Relativity Rules 1) All Physics are the same in all reference frames 2) The speed of light is observed to be constant in all reference frames No matter what motion is occurring between two (or more) reference frames: THE SPEED OF LIGHT IS ALWAYS THE SAME.

71 Relativity

72 Relativity The next example occurs based on George s perspective

73 Relativity

74 Relativity

75 Relativity

76 Relativity

77 Relativity

78 Relativity

79 Relativity Based on George s perspective, the time on the spaceship is moving slower than his time.

80 Relativity 1.0 seconds Based on George s perspective, the time on the spaceship is moving slower than his time.

81 Relativity 0.75 seconds 1.0 seconds Based on George s perspective, the time on the spaceship is moving slower than his time.

82 T G Relativity

83 Relativity T GR T G

84 Relativity T G > T GR T GR T G

85 Relativity T G > T GR T GR T G Speed of Light

86 Relativity T G > T GR T GR T G Speed of Light Since light speed is constant and George s time is larger than Gracie s: Gracie will measure lengths smaller than George will (L GR < L G )!

87 Relativity Summed Up: Means that people who are moving relative to each other each measure different times and different lengths

88 Relativity All the previous discussions were under the presumption of motion going through constant velocity!

89 Relativity All the previous discussions were under the presumption of motion going through constant velocity! It took Einstein from 1905 to 1918 to involve acceleration and gravity into relativity.

90 Acceleration, Mass, and Gravity How would you find the circumference of the circle (space-station) on your paper?

91 Acceleration, Mass, and Gravity How would you find the circumference of the circle (space-station) on your paper? 2 Ways: Find the radius Measure the circumference

92 Acceleration, Mass, and Gravity Lets have George and Gracie measure the space station while in space.

93 Acceleration, Mass, and Gravity Lets have George and Gracie measure the space station while in space. George will measure the radius; Gracie will measure the circumference.

94 Acceleration, Mass, and Gravity Lets have George and Gracie measure the space station while in space. George will measure the radius; Gracie will measure the circumference. One caveat: to simulate gravity on the space station, it has to rotate about its center!

95 Acceleration, Mass, and Gravity

96 Acceleration, Mass, and Gravity Why do George and Gracie not agree on the circumference on the space station?

97 Acceleration, Mass, and Gravity Why do George and Gracie not agree on the circumference on the space station? Length Contraction!

98 Acceleration, Mass, and Gravity Why do George and Gracie not agree on the circumference on the space station? Length Contraction!

99 Acceleration, Mass, and Gravity On your paper draw a warped circle: Then warp the paper so you see a circle

100 Acceleration, Mass, and Gravity What we find is that any type of acceleration will be due to the warping ( shape ) of space-time. Since gravity is a major type of accelerated motion, Einstein stated that with the presence of gravity in space, space-time must be warped.

101 Acceleration, Mass, and Gravity It is warped like placing some object on a pillow case.

102 Acceleration, Mass, and Gravity It is warped like placing some object on a pillow case. Mass presence in space causes space to warp; the warping of space is gravity.

103 Mass This is where we talk about black holes Any questions?