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Lect11_[Compatibility_Mode]

Lect11_[Compatibility_Mode] - Physics 344 Foundations of...

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Physics 344 Foundations of 21 st Century Physics: Relativity, Quantum Mechanics and heir Applications Their Applications Instructor: Dr. Mark Haugan Office: PHYS 282 [email protected] TA: Dan Hartzler Office: PHYS 7 [email protected] Grader: Shuo Liu Office: PHYS 283 [email protected] Office Hours: If you have questions, just email us to make an ppointment. e enjoy talking about physics! appointment. We enjoy talking about physics! Reading: Chapter 8 of the text. Notices: Exam I will be at 8:00pm Thursday, October 7 in MTHW 210

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Recitation Recap The text’s Pole & Barn puzzle and the variation on it that we analyzed yesterday illustrate ways in which the accounts of sequences of physical events can differ from one frame to another. Events occur, and there is a consistent causal explanation of the sequence in both frames, but the time ordering of some events (the ones with spacelike separations) may differ in the two frames. e considered a shed 10 ns long (measured in its rest frame e Home frame) t We considered a shed 10 ns long (measured in its rest frame – the Home frame) and a 15 ns long pole (measured in its rest frame – the Other frame ) approaching at V = 4/5 so 15 γ == t 2 3 1( 4 / 5 ) This shed-frame spacetime diagram depicts the worldline of the front of the pole, which extends as B C far as event B along the t’ axis of the Other frame. It also depicts part of the worldline of the back of the pole which crosses the x axis at x = -9 ns x A because its length is Lorentz contracted as measured in the shed frame.
t We were interested in relationships between events t A = front of pole enters the shed B = front of pole strikes the back of the shed C = back of pole enters the shed D x B C In the shed frame, t B = 12.5 ns and t C = 11.25 ns so the pole is all in one piece inside the shed for about 1.25 ns until event B occurs and the pole egins to disintegrate The shed ame diagram x A begins to disintegrate. The shed-frame diagram clearly shows event C occurring before event B, i.e., lower than B in the diagram. he time order of events C and B is reversed as measured in the pole aulter’s The time order of events C and B is reversed as measured in the pole-vaulter s frame. We show the x’ axis and the Other-frame surface of simultaneity that includes event B to make this clear. Note that the time order of these events can differ from frame to frame without disrupting causality because they have a spacelike separation. Why in this Other frame representation does the back of the pole continue into the shed as if nothing had happened at the front?

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Lect11_[Compatibility_Mode] - Physics 344 Foundations of...

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