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P221_2008_week1

# P221_2008_week1 - Swain Hall West 1 Floor Student Services...

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Swain Hall West- 1 st Floor DVB office 007 Stairs Student Services office (drop/add) o Secretary’s office

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Swain Hall West- 2 nd Floor Q. Bailey office on third floor 331 Library Physics Forum
CALM system

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CALM system
P221 Lecture 1 Welcome to P221; go over the syllabus Question: What is Physics (science in general)? Why do the objects we observe in everyday life come to rest when “left alone”? Any quantity in science has three elements: A number (3, or 2.56, or 6340.094 say). A unit (3 meters, 2.56 liters, 6240.094 seconds) An uncertainty (either explicit or implicit).

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Adding numbers requires the right UNITS!! This sign makes no sense, you can’t add years and people!
Units and Uncertainty Always check your units!! You can’t have the correct answer if your units are wrong or inconsistent! An informative website for the definition and meaning of units can be found at: http://physics.nist.gov/cuu/Units/units.html Sometimes the uncertainty in a number is expressed explicitly, sometimes implicitly: Explicit: 3.2265 +/- 0.0003 Implicit: 3.23 or 0.674 (3 sig. figs. Uncertainty is understood to be +/- 5 in the next digit, in these examples it is +/- 0.005 and +/- 0.0005 respectively). Note therefore, the relative uncertainty in 1.00 is quite different from that of 9.99. UNCERTAINTY is the key, not “number of significant figures”.

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Hints for solving problems The text gives you a number of strategies for solving problems, pay attention to them. Since it is often useful to have two views of such important matters, here is my version of the key strategic points: RTFQ!! Draw a diagram (e.g. identify all forces here). Organize the data provided, ask yourself what the question is after (explicit and implicit). Why was the question asked? Identify the crucial concept(s) and equation(s). What do you know about the quantity that is being sought and what can you relate it to? Can these be linked to the data provided? SIMPLIFY: can the problem be broken into smaller parts. SIMPLIFY: by doing some algebra before inserting numbers. Put numbers into the equation(s) (CHECK YOUR UNITS!!!) Round off to proper uncertainty (number of sig. figs.) ONLY at the end of the calculation. Check to make sure that the answer makes sense (check units, is it manifestly too large or too small, etc.) This may be easier if you can make a rough guess for the size of the answer (see below).
If someone were to suggest to you that the Earth “weighed” 1 billion billion tons (i.e. 10

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P221_2008_week1 - Swain Hall West 1 Floor Student Services...

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