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Unformatted text preview: 1 Principle of the invariance of coincidences: when one observer says two events coincide in space and time, so will all other observers. Moving Clocks run slowly Moving Sticks shrink 2 The Length of a Moving Stick: Part 1 The length of a meter stick that moves with uniform velocity along a line perpendicular to its length is the same as the length of a meter stick at rest. 10090807060504030200 10090807060504030200 The stationary meter stick A measures the length of stick B, which moves with speed v in the direction of the arrows. A B Direction of motion of stick B There is a single instant of time when B crosses A, they are on top of each other. At this moment we note the points on A that are in contact with the 0cm and 100cm points of B. If they are the 0cm and 100cm of A, the sticks are obviously of the same length. 3 The Length of a Moving Stick: Part 1 Now suppose, on the contrary, that moving stick B shrank so that, for example, the 100cm and 0cm coincided with 95cm and 0cm mark of A. 10090807060504030200 10090807060504030200 Direction of motion of stick B B A We can invoke the principle of relativity to show that this is impossible. From B point of view, A is moving, and he must also find that the 100cm and 0 cm coincided with 95cm and 0cm mark of A. So he concludes that a stick moving perpendicular to its length (for him, stick A) gets longer than the stationary sick (for him, stick B). Rule 1 : A meter stick moving with uniform velocity in a direction perpendicular to itself has the same length as a meter stick at rest. 4 Qu ickT ime and a An ima tion decompressor are needed to see th is p ic ture ....
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 Spring '08
 Alarcon
 Physics

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