Week 5 Notes
Week 5 Notes Physics 120-01
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This 3 page Class Notes was uploaded by Alexandra Graham on Friday February 20, 2015. The Class Notes belongs to Physics 120-01 at University of Massachusetts taught by Guy Blaylock in Spring2015. Since its upload, it has received 142 views. For similar materials see Big Bang to Black Hole in Physics 2 at University of Massachusetts.
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Date Created: 02/20/15
217 220 Notes 217 Reference Frame of a Photon travelling through a FINITE universe the universe appears Mand time is frozen 0 This would not be if the universe is in fact INFINITE The New Galilean Transformation Classical and Lorentz transformation equations found on slides Galilean transformation is the factor by which length contraction is derived 0 ie you use the Galilean transformation as a piece of the equation you use to gure out how much say a pole is Iength contracted at a certain speed c When you change reference frames you mix up space and time quotmy time is a mix of your space and timequot Now that we know how distance and time work you can gure out how velocity works Lorentz transformation shows mathematically how adding time dilation length contraction make any attempt to pass the speed of light really come out as a smaller number The Relativity of Simultaneity If standing still looking at exact middle of train car lighting strikes are simultaneous If standing on train as it39s moving lightning from front of car seems to have occurred rst Simutaneity is rela tive 218 The Pole and Barn Paradox Bessie the Cow quotI won t t in that length contracted barnquot Barn appears much shorter than her Farmer Guy quotBessie the length contracted cow will de nitely t in that barnquot Bessie appears to be Iength contracted while the barn seems the same size This quotparadoxquot is actually nota paradox because it is explained by Special Relativity Simultaneity is relative Farmer Guy thinks Bessie39s nose and tail will be in the barn at the same time while Bessie thinks not Relativity of Simultaneity implies that different observers do not need to agree on the order of events The Twin Story see pictures in slides Alice must be older Why 0 Because Alice is in an inertial reference frame while Bob is in an accelerated reference frame he has to slow down in order to turn around and come back 0 Special Relativity cannot accurately explain Bob39s turn around in the time it takes him to turn back Alice has aged a BUNCH 2 Emc Einstein Mass Energy same thing Small amounts of mass gtgt large amounts of energy 0 Energy of motion kinetic energy 0 Potential energy stored energy that can be turned into motion A battery stored chemical energy 0 Conservation of Energy energy is neither created nor destroyed only changes form Gravitational Potential Energy a tightrope walker is in a gravitational eld putting her up high on a tightrope adds potential energy because of the possible effects of gravity her falling kinetic energy Conservation of energy in cases involving chemical or nuclear reactions we must de ne the type of energy as Em02 2 Emc shorthand for E mreativisticcquot2 0 mass has its own stored potential energy 0 the m in the equation is relativistic depends on reference frame mlreativistic chanoes W velocity the equation for which is on slides as object speeds up mrelativistic gets BIGGER You can t get past the speed of light because things heavier as they go faster so you have to keep adding energy Eventually the object will get in nitely massive so no matter how hard you push it won t move Two Familiar and Related Consequences 1 It takes in nite force to accelerate to the speed of light 2 It takes in nite energy to accelerate to the speed of light 220 Bubble Chamber a bunch of liquid helium depressurized to almost boiling almost charged particle moves through helium and ionizes some particles catalyzing boiling so you can see a string of bubbles where the particle has moved Advanced Studies in Gravity 158039s Drop two objects they will fall at the same rate Force of gravity is proportional to the mass of the object o It takes more force to pull down a quarter than a penny so the force of the gravity acting on it much be higher quotgravitational massquot is the same as quotinertial massquot Newton39s breakthrough maybe the thing holding the moon in place is that same thing that makes apples fall to the ground The Law of Universal Gravitation 1687 equations all on slides BIG IDEA Earth is super massive so it sets off the tiny G value
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