August 18, 2014

 Why is it important for scientists to use the same system/units of measurement? GUIDING QUESTION #1

SYSTEMS OF MEASUREMENT Why do we need a standardized system of measurement?  Scientific community is global.  An international “language” of measurement allows scientists to share, interpret, and compare experimental findings with other scientists, regardless of nationality or language barriers.  Problems with the “English” system of measurement

MAP OF COUNTRIES THAT USE ENGLISH SYSTEM OF MEASUREMENT

 The first standardized system of measurement: the “Metric” system  Developed in France in 1791  Named based on French word for “measure”  based on the decimal (powers of 10)  International System of Units  Modernized version of the Metric System  Abbreviated by the letters SI.  Established in 1960, at the 11th General Conference on Weights and Measures.  Units, definitions, and symbols METRIC SYSTEM & SI

COMPONENTS OF THE SI SYSTEM  The SI system of measurement has 3 parts: 1) base units 2) derived units 3) prefixes  Base Unit: measure of the quantity that is defined to be exactly 1  Prefix: modifier that allows us to express multiples or fractions of a base unit

 What objects can you measure?  What properties can you measure? GUIDING QUESTION #2

 Distance (length, width, height)  Time  Temperature  Mass  Force (gravity)  Amount of a substance  Electric current  Luminous intensity MEASURABLE PROPERTIES

 What objects can I can measure?  What property is being measured?  Come up with five examples of each measureable property coded in red on the previous slide. EXAMPLES

 What units are written with measurements of specific properties?  What tools are used for measurable properties? GUIDING QUESTION #3

SI: BASE UNITS Physical QuantityUnit NameSymbol lengthmeterm massgramg timeseconds electric currentampereA temperatureKelvinK amount of substancemolemol luminous intensitycandelacd

SI: DERIVED UNITS Physical QuantityUnit NameSymbol areasquare meterm2m2 volumecubic meterm3m3 speed meter per second m/s acceleration meter per second squared m/s 2 weight, forcenewtonN pressurepascalPa energy, workjouleJ

SI AND ENGLISH UNIT COMPARISON SI Units  Meter  Gram  Liter  Kelvin  Mol  Cubic meter English Units  Yard  Ounce  Quart  Fahrenheit  Troy ounce  Bushel

 Using your previous examples, answer the following questions for each one.  What units are written with measurements of specific properties?  What tools are used for measurable properties? EXAMPLES

USING APPROPRIATE UNITS  In order to make our measurements as accurate and precise as possible, it is important to choose the most appropriate prefix to accompany the base unit.  For example, if I want to measure the distance & mass of a paper clip, I would use centimeters & grams. To find the distance & mass of an elephant, I would use meters & kilogram.

PrefixSymbolNumerical Multiplier Exponential Multiplier yottaY1,000,000,000,000,000,000,000, zettaZ1,000,000,000,000,000,000, exaE1,000,000,000,000,000, petaP1,000,000,000,000, teraT1,000,000,000, gigaG1,000,000, megaM1,000, kilok1, hectoh decada no prefix means:110 0 PREFIXES

PrefixSymbolNumerical Multiplier Exponential Multiplier no prefix means:110 0 decid0.110¯ 1 centic0.0110¯ 2 millim ¯ 3 micro  ¯ 6 nanon ¯ 9 picop ¯ 12 femtof ¯ 15 attoa ¯ 18 zeptoz ¯ 21 yoctoy ¯ 24

SI PREFIXES To help you remember the most practical SI prefixes, label this staircase and glue it in your notebook. You will need to memorize these!!

MEASUREMENT & PRECISION The precision of a measurement depends on the instrument used to measure it. For example, how long is this block?

MEASUREMENT & PRECISION  You should estimate one decimal point past where you can accurately measure, if the scale continues so that you can make an educated estimate.  Thus, the tool you use determines the number of significant figures used to report measurements.  Never estimate past the reading on a digital instrument.

HOW BIG IS THE BEETLE? Copyright © by Fred SeneseFred Senese Measure between the head and the tail! Between 1.5 and 1.6 in Measured length: 1.54 in The 1 and 5 are known with certainty The last digit (4) is estimated between the two nearest fine division marks.

HOW BIG IS THE PENNY? Copyright © by Fred SeneseFred Senese Measure the diameter. Between 1.9 and 2.0 cm Estimate the last digit. What diameter do you measure? How does that compare to your classmates? Is any measurement EXACT?

WHAT LENGTH IS INDICATED BY THE ARROW?