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Unformatted text preview: ISP209s9 Lecture 21 Today • Announcements: – HW#1 is due Wednesday by 8:00 am – The first LONCAPA extra credit assignment is due 1/22 by 8:00 am. • Review from last time • Units • Scalars, Vectors and Tensors • Motion and Newton’s Law of Inertia ISP209s9 Lecture 22 Review: Einstein ’s Postulates 1) Principle of Relativity: Laws of Nature are the same in all nonaccelerated ( aka “inertial”) reference frames. 2) Principle of the constancy of the Speed of Light: The speed of light in empty space is the same for all nonaccelerated (aka “inertial”) reference frames: c = 300,000 km/s From these 2 postulates and nothing more, Einstein’s Special Theory of Relativity follows ISP209s9 Lecture 23 Review: Constancy of Lightspeed “c” You might expect Mort measures the speed of Velma’s light beam to be c + .25c = 1.25c. This is NOT the case. They both get c= 300,000 km/s. c = 300,000 km/s !!! ISP209s9 Lecture 24 Review: Relativity of Time • Einstein’s simple thought experiment with “light clocks” implied some mindblowing consequences about time: – Moving clocks run slow (I.e., Time slows down) – Time is relative according to your reference frame 2 2 2 1 1 1 1 ! " " # = $ $ % & ’ ’ ( ) # = = c v t t time that elapses on your watch time that elapses on the moving watch “TimeDilation” ISP209s9 Lecture 25 Time Travel • Moving at high speed is a way to travel into the future. (E.g., the mom who returns younger than her son after taking a long, fast rocket trip while he stayed on Earth.) • We can look into the past because, although the speed of light is fast, distances in space are large. – We see the Sun as it was 8 minutes ago – We see nearby stars as they were 410 years ago – The distance light travels in one year is called a lightyear. – We see nearby galaxies as they were 1 million years ago – Looking out at the stars is like looking back in time. • We can move forward in time. Can we move backward in time? ISP209s9 Lecture 26 Clicker Question #1 ISP209s9 Lecture 27 Clicker Question #2 ISP209s9 Lecture 28 Units • Physical quantities always have a unit attached; for example, the length of the table is NOT 2, it is 2 meters. • Some quantities are a combination of units; for example 1 liter = 1000 cm 3 (LONCAPA 1000 cm^3 or 1.0E3 cm^3 or 1.0E3 m^3) • How many liters are in a gallon?...
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 Spring '10
 SB
 Inertia, General Relativity, Special Relativity, Velocity

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