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02ps-07 Size Of The Moon Solution

  • 0:00 - 0:04
    To solve this the first thing I want to know is how many moons can fit into the earth's shadow?
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    How many moons widths are there associated with this time spent in eclipse.
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    Well, 205 minutes is 3.42 hours.
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    Now, I have this conversion factor here,
  • 0:17 - 0:21
    which relates hours to moon widths, so why don't I use that?
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    3.42 hours times--well, now I want to invert this, because I want the hours to cancel out.
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    This guys has got to go downstairs.
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    Times 1 moon width per 0.93 hours. Hours cancels. Sorry. This should have been a 2.
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    This equals 3.68 moon widths.
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    Since we said the shadow was the same size as the earth,
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    this is equal to one earth width.
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    Let's divide this by 3.68, because I want to know what 1 moon width is.
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    I find it's one earth width divided by 3.68.
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    The moon is 3.68 times smaller than the earth.
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    I don't actually want width. I want circumference.
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    Let's go over here and say the moon's circumference, MC,
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    is equal to, well, 1 earth's circumference divided by 3.68.
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    That's going to be 40,000 km--that's the earth's circumference--
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    divided by 3.68, and the circumference of the moon is about 10,900 km.
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    Great work. This is really amazing.
  • 1:29 -
    You've calculated the circumference of the earth and the circumference of the moon.
Title:
02ps-07 Size Of The Moon Solution
Video Language:
English
Team:
Udacity
Project:
PH100 - Intro to Physics
Duration:
01:33
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