phy190_l01 - (c Light waves move with respect to...

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PHY190 Lecture #1 October 22, 2007 1. Introduction/WebSite (a) Textbook website (b) Tutorial Schedule (c) Tests (d) Lecture Notes (e) STORM grades (f) Contacting me by email – permission to post, replies on BulletinBoard 2. What is Special Relativity Length Contraction Time Dilation Weird effects that occur when objects move close to the speed of light. 3. How fast does light travel ( 3 × 10 8 m/s)? 1 light-year 9 . 5 × 10 15 m, 9.5 Pm (nearest stars at 4 light years). 1 light-minute 18 × 10 9 m, 18 Gm (Sun is 8 light-minutes away). 1 light-second 300 × 10 6 m, 300 Mm (Moon is 1 light-second away). 1 light-nanosecond 30 cm . .. human scale. 4. Cosmos Episode 8 – First clip Setup: Sagan (astronomer) is interested in interstellar travel. Asking the question: “How fast can we get there?”. “Why is the speed of light as fast as we can go?” (a) Einstein was a high-school dropout – big discoveries usually require thinking outside the box. (b) Relative speeds are all we can measure/observe.
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Unformatted text preview: (c) Light waves move with respect to “what”? (d) Images don’t arrive from an object traveling at v at speed v + c . 5. Cosmos Episode 8 – Second clip • Setup: What would the world look like if one were able to travel close to the speed of light? (a) Clearly not part of our everyday experience – but all tests made to date agree with special relativity. We’ll see many examples over the next few weeks. (b) Length contraction: Back of the fast body ’catches’ up to front due to high speed (approaching speed of light) ⇒ length contraction (c) Images in “front” are blue-shifted (shorter wavelengths of light), peripheral images (and “behind”) are receding at close to speed of light and thus red-shifted (longer wavelengths of light). (d) Time dilation ⇒ twin paradox – harder to ’see’ physically but will be a consequence of our math....
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