Week 4 Notes
Week 4 Notes Physics 120-01
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This 2 page Class Notes was uploaded by Alexandra Graham on Friday February 13, 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 76 views. For similar materials see Big Bang to Black Hole in Physics 2 at University of Massachusetts.
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Date Created: 02/13/15
Week 4 Notes No Monday again Holy cannoli 2 11 Einstein no object nor anything useful can travel faster than light 0 No messages Nada Discussion When the shadow of a bug travelling half the speed of the light appears to travel faster than the speed of light Special Relativity is NOT violated because the light is the medium carrying the shadow Our perception just lies to us Time Dilation Photon clock beam of light bouncing between two mirrors Traveling from bottom to top tick travelling from top to bottom again tock Synchronized with your Rolex it s a light clock If a photon clock is rapidly moving past you the beam will appear to move diagonally rather than up and down making it seem like the light is travelling at a longer distance 0 Naturally it must take longer for the light to tick tock 0 But NO instead time dilates slows down to stay in time with the speed of light Time dilation is true of ALL CLOCKS even your biological clock It is a testament to how time works not how photon clocks work 2 13 Time Dilation Cont d Cosmic Muons elementary particles like an electron but 200x heavier decay after 2x10quot6 seconds Travel from the upper atmosphere to earth s surface 3920 kilometers before they decay BUT WAIT To travel that distance so quickly they would have to travel at 30x THE SPEED OF LIGHT How do they do it TIME DILATION they travel so quickly that their biological clocks slow down meaning they decay much slower from our perspective From the perspective of the muon though it s time isn t slowing Earth is just length contracted Length Contraction Set one photon clock straight up tilt another photon clock next to it on its side then shoot them both to the right gtgtgtgtgtgtgtgtgtgt Both clocks will be in sync even though the beam from the tilted clock has to travel a longer distance 0 Why If you could see one clock slowing down you would be able to tell you were moving in an inertial reference frame and the theory of Relativity would be wrong o How Length is relative The length of the tilted clock is smaller the distance between the mirrors is shorter the beam of light does not have to travel as far
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