228s12-l09 - Physics 228 Today Introduction to(Special...

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Physics 228 Today: Introduction to (Special) Relativity Website: Sakai 01:750:228 or www.physics.rutgers.edu/ugrad/228 First exam (Thursday, Feb 23, 9:40 PM) room assignments: Physics Lecture Hall: sections 03, 16, 20, 22 - Profs. Salur and Basirnia ARC 103: sections 02, 04, 05, 06, 14, 15, 21 - Profs Cizewski, Zamolodchikov You are allowed 1 formula sheet (both sides may be used, any size font you want), pencils, and a calculator calculator. Contact Prof. Salur if you have conflicts or last-minute issues that prevent you from taking the exam. Thursday, February 16, 2012
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Special Relativity 1st postulate (assumption): Physical laws are the same in every inertial reference frame. 2nd postulate: speed of light is the same in every inertial reference frame The first might seem obvious, but the second is not how we add velocities. Let’s work through this. Thursday, February 16, 2012
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What is a Reference Frame? A coordinate system that tells us where things are. right left +x up +y If I demonstrate, for example, dropping a ball, you and J. Stick Figure, shown to the left, both at rest in the lecture hall, will describe the same motion, except for a simple transformation. Perhaps: t you = t JSF + t off x you = -x JSF + x off y you = y JSF + y off z you = -z JSF + Z off front +z Different people can have different reference frames / coordinate systems. Both you & JSF see F = -mg ŷ , and Δ y = ½ g(t-t 0 ) 2 . Thursday, February 16, 2012
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What is an Inertial Reference Frame? An inertial reference frame is a reference frame that is not accelerating. The idealized inertial reference frame is being on a spaceship, engines turned off, far from the sun, with no external forces. (Gravity is small enough to neglect.) While we usually think of us here on the surface of the earth as being in a fixed non-accelerating reference frame, we are not - the earth is rotating. But for many purposes, if we are not too precise in our measurements, we can approximate our on-the-surface-of-the- earth frame as an inertial reference frame. And we do so for most of this lecture. Thursday, February 16, 2012
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Inertial Reference Frames? Let’s consider dropping the ball again. You and JSF are still, but I walk left to right at constant speed. JSF would say I move at speed v to +x.
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