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# Space travel the speed of light we cant always ignore

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Unformatted text preview: ething is when it happened (at least for events here on Earth). You can determine how far away a lightning strike is by counting seconds from the time you see the lightning until you hear the thunder. It takes sound about 5 s to travel a mile, so if the thunder lags behind the lightning by 2 or 3 s, then the lightning strike occurred about half a mile away. Problem: You hear a thunder clap 6 s after you see the lightning. Assume the speed of sound to be 343 m/s. How far away is the lightning? (Solution on next slide) Light Vs. Sound (cont.) Answer: Ignoring the small amount of time light needs to travel to you, we have: d = v t = (343 m/s) (6 s) = 2058 m Problem: Now let’s do the same problem without ignoring light’s travel time: Light Waves Sound Waves Solution on next slide Light Vs. Sound (cont.) Answer: Let t = time it takes the light to reach you. In that time the sound of the thunder only travels a short distance. Since you hear the thunder 6 s after you see the lightning, the sound travels for (6 s) + t. The light and sound each travel the same distance, so: ⇒...
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