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Modern Physics

Modern Physics. Time to Blow your Mind!!!. Relativity. Motion is relative Frame of reference= the place from which motion is observed and measured EX: You and your friend are on a train….is your friend moving? How about if you are on the ground next to the train?. Beginnings of Relativity.

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Modern Physics

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  1. Modern Physics Time to Blow your Mind!!!

  2. Relativity • Motion is relative • Frame of reference= the place from which motion is observed and measured • EX: You and your friend are on a train….is your friend moving? How about if you are on the ground next to the train?

  3. Beginnings of Relativity • Thought the detection of motion through the ether might be measurable • In trying to measure the speed of the Earth through the supposed "ether", you could depend upon one component of that velocity being known - the velocity of the Earth around the sun, about 30 km/s. • Using a wavelength of about 600 nm, there should be a shift of about 0.04 fringes as the spectrometer was rotated 360°. Though small, this was well within Michelson's capability. Michelson, and everyone else, was surprised that there was no shift. • Although repeated over the next 40 years with ever greater precision and the same negative result, this 1887 experiment is pointed to as one of the experimental foundations of relativity, and earned Michelson the Nobel Prize in 1907. • Final Conclusion= the measurement of absolute velocity is not possible!

  4. Special Theory of Relativity • The physical theory of measurement in inertial frames of reference proposed in 1905 by Albert Einstein (after the considerable and independent contributions of Hendrik Lorentz, Henri Poincaré and others) • It generalizes Galileo's principle of relativity—that all uniform motion is relative, and that there is no absolute and well-defined state of rest (no privileged reference frames)—from mechanics to all the laws of physics, including both the laws of mechanics and of electrodynamics, whatever they may be

  5. Postulates of STR • 1. All laws of nature are the same in all uniformly moving frames of reference • Basically, the laws of physics in a uniformly moving airplane are the same as those in a stationary lab • The speed of light in free space has the same measured value for all observers, regardless of the motion of the source or the motion of the observer • The speed of light is a constant

  6. Conceptual Framework • Framework of STR • We will go into some of these concepts in more detail a little later

  7. Simultaneity • Two events are simultaneous if they happen at the same time • EX: When light bulb in the exact center of a spaceship is switched on the light spreads out in all directions at speed c. • Because the bulb is equidistant from the front and the back of the ship the light reaches the front of the ship at the same time it reaches the back of the ship • This will happen if the ship is at rest or has a constant velocity

  8. Simultaneity • Now, consider an outside observer who views the same two events (light reaching the front and light reaching the back of the ship) from another frame of reference….a planet NOT moving with the ship • Now the two events are NOT simultaneous! • The observer sees the light reach the back before it reaches the front • Soooo, we can reach the conclusion that two events that are simultaneous in one frame of reference need not be simultaneous in a frame moving relative to the first frame

  9. Time Dilation • Can time be stretched? • Consider the following scenario….

  10. Time Dilation • The longer the distance covered by the light flash in following the longer diagonal path below must be divided by a correspondingly longer time interval to yield an unvarying value for the speed of light! Distance = Distance =c Time Time

  11. Time Dilation • So, if this is true for a light clock is it true for any kind of clock? • YES • All clocks run more slowly when moving than when at rest • Time dilation has to do not with the mechanics of clocks but with the nature of time itself • The relationship of time dilation is derived from the following

  12. Time Dilation • If it were possible to make a clock fly by you at the speed of light the clock would not appear to be running at all! • Time dilation has been confirmed in the lab with particle accelerators. • The lifetime of fast-moving radioactive particles increase as the speed goes up, and the amount of increase is just what Einstien’s equation predicts

  13. The Twin Trip Paradox!!!! • TIME TO BLOW YOUR MIND! • http://player.discoveryeducation.com/index.cfm?guidAssetId=2ECA67DB-C0DB-4E93-AEC1-5E7FA99F1A1C&blnFromSearch=1&productcode=US

  14. Length Contraction • The length of any object in a moving frame will appear foreshortened in the direction of motion, or contracted. • The amount of contraction can be calculated from the Lorentz transformation. • The length is maximum in the frame in which the object is at rest.

  15. Length Contraction • Lorenz Transformation

  16. Length Contraction • Simulation

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