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# Lec2 - Physics 2A Lecture 2 Today Estimation Variables of...

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Today: Estimation. Variables of motion. Physics 2A Olga Dudko UCSD Physics Lecture 2

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Estimation • Sometimes there will not be an easily found, exact answer available for a given problem. • In this case, you must estimate estimate certain values in order to continue. • Example : what if you were asked to fi nd the volume of a cow? • A fi rst order estimate: assume that the cow is a sphere • Estimates are designed to get you close to the answer with ease (say within a factor of ten). => V cow = 4/3 ± R 3
How many piano tuners are there in Chicago? Solution Solution First we should fi nd out how many pianos there were in Chicago… Physicist Enrico Fermi was known for his estimation prowess. At a party (in the late 60’s), he was approached by someone and asked: “How many piano tuners are there in Chicago?” Enrico Fermi, Nobel Prize in Physics (1938)

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Estimation Solution (cont Solution (cont d) d) • Fermi fi rst estimated how many people lived in Chicago, at the time it was 700,000. • He then guessed that 1 out of 3 families owns a piano. • Assuming a family is about 4 people this means 1 out of 12 people have a piano. We round this to 1 out of 10 for ease. • This means that there were about 70,000 pianos in Chicago at that time.
Estimation Solution (cont Solution (cont d) d) • Next, Fermi turned to how many piano tuners could get work for 70,000 pianos. • He fi rst determined that it took 1 to 2 hours to tune a piano. • Thus, a piano tuner could service about four pianos a day.

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Lec2 - Physics 2A Lecture 2 Today Estimation Variables of...

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