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# W1.3 - Physics for Scientists Engineers 1 Spring Semester...

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January 8, 2008 Physics for Scientists&Engineers 1 1 Physics for Scientists & Physics for Scientists & Engineers 1 Engineers 1 Spring Semester 2008 Lecture 3

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January 8, 2008 Physics for Scientists&Engineers 1 2 Few Points Few Points Homework First four homework sets opened (In case you might want to work ahead) Homework Set 1 due by Friday 23:59 Help room starts on Thursday TA office hours in Strosacker Thursday: Jon: 2 - 5 pm, Kyaw Zin: 5 - 7 pm Friday: Jon: noon ~ 4 pm, Kyaw Zin: 4 - 9 pm Honors option: today is last chance to enroll or change the hours in the help room
January 8, 2008 Physics for Scientists&Engineers 1 3 Scientific Notation Scientific Notation Physical quantities consist of a number that specifies its magnitude AND its unit Example: this lecture lasts 50 minutes (number) (unit) For very large or very small numbers, we use scientific notation Example: 3.2·10 -12 (or 3.2x10 -12 ) Product easy: (4.8x10 -17 )x(7.21x10 7 )=34.6x10 -10 =3.46x10 -9 You can enter number in scientific notation into the LON- CAPA homework system as 3.2e-12 or 3.2*10^-12 number = mantissa ! 10 exponent

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January 8, 2008 Physics for Scientists&Engineers 1 4 Significant Figures Significant Figures Two statements: The population of the USA is 294,109,799 The population of the USA is 294,000,000=2.94·10 8 First statement implies precision that is simply not warranted Second statement claims that the population is somewhere between 293M and 295M. This is justified! General Rule: The number of digits we write down in a number specifies the precision with which we claim to know that number. US Census Bureau August 2004
January 8, 2008 Physics for Scientists&Engineers 1 5 Example: Significant Figures Example: Significant Figures Suppose we are told that the radius of a circle is 2.66 feet; what is its circumference? Formula: Type into your pocket calculator and get: 16.7132729170977 But if we only know that the radius of the circle is between 2.65 and 2.67 feet, i.e. to 3-digit precision, then we cannot claim that we know the circumference of the same circle to better than 3 digits.

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W1.3 - Physics for Scientists Engineers 1 Spring Semester...

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