Chapter_1-pre-lecture

# Chapter_1-pre-lecture - Often useful as a sanity check (for...

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Physics (and science in general) is all about building models, and confronting those models by comparing them to the ‘real world’. Measurements require standards, and we will use the international (metric) system. Physics and measurement

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Standard of Time Time – second (s) (1/60)(1/60)(1/24) of a solar day. 9 192 631 770 times the period of vibration of radiation from the cesium atom.
Smallest Atomic Clock

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Standard of Length Length – meter (m) 1/10 000 000 of the distance equator – north pole 1/299 792 458 of the distance traveled by light in one second
Standard of Mass Mass – kilogram (kg) Model kilogram kept at the International Bureau of Weights and Measures in France.

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Derived units Things like speed, density are derived units:
There are many customary units, which are in use either for historical or practical reasons 1 mile = 1 609 m; 1 ft = 0.304 8 m; 1 in. = 0.025 4 m Speed limit on a Vermont highway: 55 mph Conversion of Units

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Unformatted text preview: Often useful as a sanity check (for example, of an equation) Treat dimensions (units) as algebraic quantities Dimensional analysis Estimates and Order-of-Magnitude Calculations Order-of-Magnitude: Correct within a factor of ten Eg: Estimate the annual gas consumption of cars in Canada Significant Figures Significant figure is the number of reliably known digits. Leading zeros are not significant. Trailing zeros are ambiguous: The last digit of 1500 could be known exactly, or could be approximated. Correct treatment: Use scientific notation. Significant Figures -Multiplication Multiplication and Division: Significant figures of the result should be adjusted to the significant figures of the factor with the lowest number of significant figures. Significant Figures -Addition Addition and subtraction: Number of decimal places in the result should equal the smallest number of decimal places in any term....
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## This note was uploaded on 08/17/2010 for the course PHYS PHYS 131 taught by Professor Ragan during the Spring '09 term at McGill.

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Chapter_1-pre-lecture - Often useful as a sanity check (for...

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