Physics III PH 113
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This 21 page Class Notes was uploaded by Jalon Willms on Monday October 19, 2015. The Class Notes belongs to PH 113 at Rose-Hulman Institute of Technology taught by Renat Letfullin in Fall. Since its upload, it has received 11 views. For similar materials see /class/225113/ph-113-rose-hulman-institute-of-technology in Physics 2 at Rose-Hulman Institute of Technology.
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Date Created: 10/19/15
Physics 1 1 3 Lecture 1 7 Special Relativity Today s Lecture will cover chapter 36 sections 1 7 Take a look at Special Relativity in 14 Easy Hyper essons htt webhe uiuceduhome o inrelativi Physics 102 Lecture 17 Slide 1 Inertial Reference Frame Review of Test 4 Frame in which Newton s Laws Work Moving is OK but No Accelerating No Rotating Technically Earth is not inertial but it s close enough Physics 102 Lecture 17 Slide 2 Postulates of Relativity Laws of physics are the same in every inertial frame Perform experiment on train going east gives same results as on train going west Speed of light in vacuum is c for everyone Measure c3XlO8 ms if you are on train going east or on train going west even if light source isn t on the train Physics 102 Lecture 17 Slide 3 Relative Velocity Ball Throw a ball at 30 mph How fast do I think it goes Whenl am Standing still I k I R39 15 ht d 3933 unning mp owar s 4 9 Running 15 mph away 4 I Physics 102 Lecture 17 Slide 4 Relatlve Velomty nght Throw photon 3X108 ms How fast do I think it goes When I am Standing still 3x108 ms r 8 Running 15X10 ms towards 3x108 mS r 8 Running 15X10 ms away 3x108 mS Strange but True It was verified in experiments with Physics 102 Lecture 17 Slide STEm n S d e The Relativity of Simultaneity A flash of light is emitted from the exact center of a box Does the light reach all the sides at the same time At Rest Moving Physics 102 Lecture 17 Slide 6 The Relativity of Simultaneity Afflas39h of light is eymifittjedifrom the exact center of 39a box D39o es the Ilig reach all th qusid at the same time At Rest YES Moving NO Simultaneous depends on frame Physics 1102 Lecture1739511de39739 The Relativity of Simultaneity httpwebhepuiuceduhomeq qollinre39lativitvp112 relativity 8html Relativity of Simultaneity Two events occurring simultaneously in reference frame S are not simultaneous in any reference frame 8 that is moving relative to S Physics 102 Lecture 17 Slide 8 Time Dilation Ato is proper time Because it is rest frame of event Physics 102 Lecture 17 Slide 9 Time Dilation e C Because it is rest frame of event Physics 102 17 Slide 10 Time Dilation You and a friend are having a drinking contest Your friend is on a train traveling at speed v09 o By her watch she finishes her drink in 5 seconds Determine the time you measure if you are standing still at the train station Since drinking is happening on the train that is the proper time Physics 102 Lecture 17 Slide 11 Time Dilation 2 Now it is your turn to drink According to your watch you finish your drink in 5 seconds How long does your friend think it took you to finish the d nk Now drinking is happening at the station so that is the proper time Both people think they won Physics 102 Lecture 17 Slide 12 Space Travel Alpha Centauri is 43 lightyears from earth It takes light 43 years to travel from earth to Alpha Centauri How long would people on earth think it takes for a spaceship traveling v095c to reach AC V C How long do people on the ship think it takes People on ship have proper time they see earth leave and Alpha Centauri arrive Ato 451 952 Ato 14 years Twin Paradox Twins decide that one will travel to Alpha Centauri and back at 0950 while the other stays on earth Compare their ages when they meet on earth Earth twin thinks it takes 2 x 45 9 years Traveling twin thinks it takes 2 x 14 28 years Traveling twin will be younger Note Traveling twin is NOT in inertial frame Physics 102 Lecture 17 Slide 14 Length Contraction People on ship and on earth agree on relative velocity v 095 0 But they disagree on the time 45 vs 14 years What about the distance between the planets EarthAlpha ol0 v t 95 3x1 08 ms 45 years 4x1 016m 43 light years Ship d v t 95 3x1 08 ms 14 years 1 25x1016m 13 light years Length in moving frame Length in object s restframe Physics 102 Lecture 17 Slide 15 Length Contraction Gifs v01 c v08 c v095 c Physics 102 17 Slit W Concept question You re eating a burger at the interstellar cafe in outer space your spaceship is parked outside A speeder zooms by in an identical ship at half the speed of light From your perspective their ship looks longer than your ship 1 horter than yo 3 exactly the same as your ship In the speeder s reference frame gt L Y J LIn your reference frame Always lt1 Physics 102 Lecture 17 Shde 17 Comparison Time Dilation vs Length Contraction AtO time in same reference frame as event ie if event is clock ticking then At0 is in the reference frame of the clock even if the clock is in a moving spaceship Time seems longer gt At Nquot from outside L0 length in same reference frame as object length of the object when you don t think it s moving V ength seems shorter I L LO 1 Ci L0 gt L from outside Relativistic Momentum mv Relativistic Momentum 9 2 1V 7 C Note for vltltc pmv Note for vc pinfinity Relativistic Energy Note forv0 E mc2 Note for vltltc E mc2 12 mv2 Note for vc E infinity if mltgt 0 Objects with mass can t go faster than 0 Physics 102 Lecture 17 Slide 19 Summary Physics works in any inertial frame Simultaneous depends on frame Proper frame is Where event is at same place or object is not moving Time dilates Length contracts EnergyMomentum conserved For vltltc reduce to Newton s Laws Physics 102 Lecture 17 Slide 20 Good Luck on the Exam Physics 102 Lecture 17 Slide 21
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