2.6 si units the international system of units, si, is a revised version of the metric system the...
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2.6 SI Units2.6 SI Units
The International System of Units, SI, is The International System of Units, SI, is a revised version of the metric systema revised version of the metric system
Correct units along with numerical Correct units along with numerical values are critical when communicating values are critical when communicating measurements.measurements.
The are seven base SI units (Table 2.1) The are seven base SI units (Table 2.1) of which other SI units are derived.of which other SI units are derived. Sometimes non-SI units are preferred for Sometimes non-SI units are preferred for
convenience or practical reasonsconvenience or practical reasons
2.6 SI Units – Table 2.22.6 SI Units – Table 2.2QuantityQuantity SI Base or Derived SI Base or Derived
UnitUnitNon-SI UnitNon-SI Unit
LengthLength meter (m)meter (m)
VolumeVolume cubic meter (mcubic meter (m33)) literliter
MassMass kilogram (kg)kilogram (kg)
DensityDensity grams per cubic grams per cubic centimeter (g/cmcentimeter (g/cm33); ); grams per mililiter grams per mililiter (g/mL)(g/mL)
TemperatTemperatureure
kelvin (K)kelvin (K) degree Celcius (°C) degree Celcius (°C)
TimeTime second (s)second (s)
PressurePressure Pascal (Pa)Pascal (Pa) atmosphere (atm); atmosphere (atm); milimeter of mercury milimeter of mercury (mm Hg)(mm Hg)
EnergyEnergy joule (J)joule (J) calorie (cal)calorie (cal)
Common SI Prefixes Common SI Prefixes
Units larger than the base unitUnits larger than the base unit
TeraTera TT ee1212 base base unitsunits
termeter (Tm)termeter (Tm)
GigaGiga GG ee9 9 base base unitsunits
gigameter gigameter (Gm)(Gm)
MegaMega MM ee6 6 base base unitsunits
megameter megameter (Mm)(Mm)
KiloKilo kk ee3 3 base base unitsunits
kilometer kilometer (km)(km)
HectoHecto hh ee2 2 base base unitsunits
hectometer hectometer (hm)(hm)
DekaDeka dada ee1 1 base base unitsunits
decameter decameter (dam)(dam)
Base Base UnitUnit
ee0 0 base base unitsunits
meter (m)meter (m)
Common SI PrefixesCommon SI Prefixes
Units smaller than the base unit Units smaller than the base unit
Base Base UnitUnit
ee0 0 base base unitsunits
meter (m)meter (m)
DeciDeci dd ee-1 -1 base base unitsunits
decimeter decimeter (dm)(dm)
CentiCenti cc ee-2 -2 base base unitsunits
centimeter centimeter (cm)(cm)
MilliMilli mm ee-3 -3 base base unitsunits
millimeter millimeter (mm)(mm)
MicroMicro μμ ee-6 -6 base base unitsunits
micrometer micrometer ((μμm)m)
NanoNano nn ee-9 -9 base base unitsunits
Nanometer Nanometer (nm)(nm)
PicoPico pp ee-12 -12 base base unitsunits
picometer picometer (pm)(pm)
Common SI PrefixesCommon SI Prefixes
A mnemonic device can be used to A mnemonic device can be used to memorize these common prefixes in memorize these common prefixes in the correct order:the correct order: TThe he GGreat reat MMonarch onarch KKing ing HHenry enry DDied ied
BBy y DDrinking rinking CChocolate hocolate MMocha ocha MMilk ilk NNot ot PPilsnerilsner
2.7 Units of Length2.7 Units of Length
The basic unit of length is the The basic unit of length is the metermeter Prefixes can be used with the base Prefixes can be used with the base
unit to more easily represent small unit to more easily represent small or large measurementsor large measurements Example: A hyphen (12 point font) Example: A hyphen (12 point font)
measures about 0.001 m or 1 mm.measures about 0.001 m or 1 mm. Example: A marathon race is Example: A marathon race is
approximately approximately
42,000 m or 42 km.42,000 m or 42 km.
2.7 Concept Practice2.7 Concept Practice
15. Use the tables in the text to order 15. Use the tables in the text to order these lengths from smallest to these lengths from smallest to largest.largest.
a. centimetera. centimeter
b. micrometerb. micrometer
c. kilometerc. kilometer
d. millimeterd. millimeter
e. metere. meter
f. decimeterf. decimeter
- 1 (smallest)- 1 (smallest)
- 2- 2
- 3- 3
- 4- 4- 5- 5
- 6 (largest)- 6 (largest)
2.8 Units of Volume2.8 Units of Volume
The space occupied by any sample of The space occupied by any sample of matter is called its matter is called its volumevolume The volume ofThe volume of rectangular solids rectangular solids can can
be calculated by multiplying the be calculated by multiplying the lengthlength by by widthwidth by by heightheight Units are cubed because you are measuring Units are cubed because you are measuring
in 3 dimensionsin 3 dimensions Volume ofVolume of liquids liquids can be measured can be measured
with a with a graduated cylindergraduated cylinder, a , a pipetpipet, a , a buretburet, or a , or a volumetric flaskvolumetric flask
2.8 Units of Volume2.8 Units of Volume
A convenient unit of measurement for A convenient unit of measurement for volume in everyday use is the liter (L)volume in everyday use is the liter (L)
Milliliters (mL) are commonly used for Milliliters (mL) are commonly used for smaller volume measurements and smaller volume measurements and liters (L) for larger measurementsliters (L) for larger measurements 1 mL = 1 cm1 mL = 1 cm33
10 cm x 10 cm x 10 cm = 1000 cm10 cm x 10 cm x 10 cm = 1000 cm33 = 1 L = 1 L
2.8 Units of Volume2.8 Units of Volume
2.8 Concept Practice2.8 Concept Practice
17. From what unit is a measure of 17. From what unit is a measure of volume derived?volume derived?
A: Volume is a length measurement A: Volume is a length measurement cubed.cubed.
2.8 Practice2.8 Practice
18. What is the volume of a paperback 18. What is the volume of a paperback book 21 cm tall, 12 cm wide, and 3.5 book 21 cm tall, 12 cm wide, and 3.5 cm thick?cm thick?
A: 882 cmA: 882 cm33 → → 880 cm880 cm33; ; 8.8 x 108.8 x 102 2 cmcm33
19. What is the volume of a glass 19. What is the volume of a glass cylinder with an inside diameter of 6.0 cylinder with an inside diameter of 6.0 cm and a height of 28 cm?cm and a height of 28 cm?
V=V=ππrr22hh
A: A: 790 cm790 cm33; ; 7.9 x 107.9 x 102 2 cmcm33
2.9 Units of Mass2.9 Units of Mass A person on the moon would weigh 1/6 of A person on the moon would weigh 1/6 of
his/her weight on Earth.his/her weight on Earth. This is because the force of gravity on the This is because the force of gravity on the
moon is approximately 1/6 of its force of Earth.moon is approximately 1/6 of its force of Earth. Weight is a forceWeight is a force – it is a measure of the pull – it is a measure of the pull
on a given mass by gravity; it can change by on a given mass by gravity; it can change by location.location.
Mass is the quantity of matter an Mass is the quantity of matter an object containsobject contains Mass remains constant regardless of location.Mass remains constant regardless of location.
Mass v. WeightMass v. Weight
2.9 Units of Mass2.9 Units of Mass
The The kilogramkilogram is the basic SI unit of is the basic SI unit of massmass It is defined as the mass of 1 L of water It is defined as the mass of 1 L of water
at 4°C.at 4°C. A gram, which is a more commonly A gram, which is a more commonly
used unit of mass, is 1/1000 of a used unit of mass, is 1/1000 of a kilogramkilogram 1 gram = the mass of 1 cm1 gram = the mass of 1 cm33 of water at of water at
4°C.4°C.
2.9 Concept Practice2.9 Concept Practice20. As you climbed a mountain and the force 20. As you climbed a mountain and the force
of gravity decreased, would your weight of gravity decreased, would your weight increase, decrease, or remain constant? increase, decrease, or remain constant? How would your mass change? Explain.How would your mass change? Explain.
A: Your weight would decrease; mass would A: Your weight would decrease; mass would remain constant.remain constant.
21. How many grams are in each of these 21. How many grams are in each of these quantities?quantities?
a. 1 cga. 1 cg b. 1 b. 1 μμgg c. 1 kgc. 1 kg d. 1mgd. 1mg
A: 0.01g 0.000001g 1000g 0.001 gA: 0.01g 0.000001g 1000g 0.001 g
2.10 Density2.10 Density
DensityDensity is the ratio of the is the ratio of the massmass of of an object to its an object to its volumevolume..
Equation →Equation → D = mass/volumeD = mass/volume Common units: g/cmCommon units: g/cm33 or g/mL or g/mL Example: 10.0 cmExample: 10.0 cm33 of lead has a mass of lead has a mass
114 g114 g
Density (of lead) = 114 g / 10.0 cmDensity (of lead) = 114 g / 10.0 cm33 = = 11.4 g/cm11.4 g/cm33
See Table 2.7, page 46See Table 2.7, page 46
2.10 Density2.10 Density
Density determines if an object will Density determines if an object will float in a fluid substance.float in a fluid substance. Examples: Ice in water; hot air risesExamples: Ice in water; hot air rises
Density can be used to identify Density can be used to identify substancessubstances See Table 2.8, page 46See Table 2.8, page 46
2.10 Concept Practice2.10 Concept Practice
22. The density of silver is 10.5 g/cm22. The density of silver is 10.5 g/cm33 at 20°C. What happens to the at 20°C. What happens to the density of a 68-g bar of silver that is density of a 68-g bar of silver that is cut in half?cut in half?
A: Its density does not change.A: Its density does not change.
2.10 Concept Practice2.10 Concept Practice
23. A student finds a shiny piece of metal 23. A student finds a shiny piece of metal that she thinks is aluminum. In the lab, that she thinks is aluminum. In the lab, she determines that the metal has a she determines that the metal has a volume of 245 cmvolume of 245 cm33 and a mass of 612 g. Is and a mass of 612 g. Is the metal aluminum?the metal aluminum?A: Density = 2.50 g/cmA: Density = 2.50 g/cm33; the metal is not ; the metal is not aluminum.aluminum.
24. A plastic ball with a volume of 19.7 cm24. A plastic ball with a volume of 19.7 cm33 has a mass of 15.8 g. Would this ball sink has a mass of 15.8 g. Would this ball sink or float in a container of gasoline?or float in a container of gasoline?A: Density = 0.802 g/cmA: Density = 0.802 g/cm33; the ball will ; the ball will sink.sink.
2.10 Specific Gravity 2.10 Specific Gravity (Relative Density)(Relative Density)
Specific gravitySpecific gravity is a comparison of the is a comparison of the density of a substance to the density of a density of a substance to the density of a reference substance, usually at the same reference substance, usually at the same temperature.temperature. Water at 4°C, which has a density of 1 g/cm3, Water at 4°C, which has a density of 1 g/cm3,
is commonly used as a reference substance.is commonly used as a reference substance.Specific gravity = Specific gravity = density of substance (g/cm3)density of substance (g/cm3)
density of water (g/cm3)density of water (g/cm3) Because units cancel, a measurement of Because units cancel, a measurement of
specific gravity has no unitsspecific gravity has no units A hydrometer can be used to measure the A hydrometer can be used to measure the
specific gravity of a liquid.specific gravity of a liquid.
2.11 Concept Practice2.11 Concept Practice
25. Why doesn’t a measurement of specific 25. Why doesn’t a measurement of specific gravity have a unit?gravity have a unit?
A: Because it is a ratio of two density A: Because it is a ratio of two density measurements, the density units cancel measurements, the density units cancel out.out.
26. Use the values in Table 2.8 to calculate 26. Use the values in Table 2.8 to calculate the specific gravity of the following the specific gravity of the following substances.substances.
a. Aluminuma. Aluminum b. Mercuryb. Mercury c. icec. ice
A: 2.70A: 2.70 13.6 13.6 0.917 0.917
2.12 Measuring 2.12 Measuring TemperatureTemperature
Temperature determines the direction of Temperature determines the direction of heat transfer between two objects in heat transfer between two objects in contact with each other.contact with each other. Heat moves from the object at the Heat moves from the object at the higher higher
temperaturetemperature to the object at a to the object at a lower lower temperature.temperature.
TemperatureTemperature is a measure of is a measure of the degree the degree of hotness or coldness of an objectof hotness or coldness of an object..
Almost all substances expand with an Almost all substances expand with an increase in temperature and contract with increase in temperature and contract with a decrease in temperaturea decrease in temperature An important exception is waterAn important exception is water
2.12 Measuring 2.12 Measuring TemperatureTemperature
There are various temperature There are various temperature scalesscales
On the On the CelsiusCelsius temperature scale temperature scale the the freezing point of water is freezing point of water is taken as 0°Ctaken as 0°C and the and the boiling point boiling point of water at 100°Cof water at 100°C
2.12 Measuring 2.12 Measuring TemperatureTemperature
The The Kelvin scaleKelvin scale (or absolute scale) is (or absolute scale) is another temperature scale that is usedanother temperature scale that is used On the Kelvin scale the freezing point of On the Kelvin scale the freezing point of
water is water is
273 K273 K and the boiling point is and the boiling point is 373 K373 K (degrees are not used).(degrees are not used).
1°C = 1 Kelvin1°C = 1 Kelvin The zero point (0 K) on the Kelvin scale is The zero point (0 K) on the Kelvin scale is
called called absolute zeroabsolute zero and is equal to -273°C and is equal to -273°C Absolute zero is where all molecular motion stopsAbsolute zero is where all molecular motion stops
2.12 Measuring 2.12 Measuring TemperatureTemperature
Converting Temperatures:Converting Temperatures: K = °C + 273K = °C + 273 °C = K - 273°C = K - 273
2.12 Concept Practice2.12 Concept Practice
27. Surgical Instruments may be 27. Surgical Instruments may be sterilized by heating at 170°C for 1.5 sterilized by heating at 170°C for 1.5 hours. Convert 170°C to kelvins.hours. Convert 170°C to kelvins.
A: K = 170°C + 273 = 443 KA: K = 170°C + 273 = 443 K
28. The boiling point of the element 28. The boiling point of the element argon is 87 K. What is the boiling argon is 87 K. What is the boiling point of argon in °C?point of argon in °C?
A: °C = 87 K – 273 = -186°CA: °C = 87 K – 273 = -186°C
2.13 Evaluating 2.13 Evaluating MeasurementsMeasurements
Accuracy in measurement depends on Accuracy in measurement depends on the the quality of the measuring quality of the measuring instrumentinstrument and the and the skill of the skill of the person using the instrumentperson using the instrument.. Errors in measurement could have various Errors in measurement could have various
causescauses In order to evaluate the accuracy of a In order to evaluate the accuracy of a
measurement, you must be able to measurement, you must be able to compare it to the true or compare it to the true or accepted accepted valuevalue..
2.13 Evaluating 2.13 Evaluating MeasurementsMeasurements
accepted valueaccepted value – the true or correct – the true or correct value based or reliable referencesvalue based or reliable references
experimental valueexperimental value – the measured – the measured value determined in the experimentvalue determined in the experiment
The difference between the The difference between the accepted valueaccepted value and the and the experimental valueexperimental value is the is the errorerror.. error = accepted value – experimental error = accepted value – experimental
valuevalue
2.13 Evaluating 2.13 Evaluating MeasurementsMeasurements
The The percent errorpercent error is the is the errorerror divided by the divided by the accepted valueaccepted value, , expressed as a percentage of the expressed as a percentage of the accepted value.accepted value.
Percent Error =Percent Error = x 100 x 100
An error can be positive or negative, An error can be positive or negative, but an absolute value of error is used but an absolute value of error is used so that the percentage is positiveso that the percentage is positive
|error||error| AVAV
2.13 Concept Practice2.13 Concept Practice
32. A student estimated the volume of a 32. A student estimated the volume of a liquid in a beaker as 200 mL. When liquid in a beaker as 200 mL. When she poured the liquid into a graduated she poured the liquid into a graduated cylinder she measured the value as cylinder she measured the value as 200 mL. What is the percent error of 200 mL. What is the percent error of the estimated volume from the beaker, the estimated volume from the beaker, taking the graduated cylinder taking the graduated cylinder measurement as the accepted value?measurement as the accepted value?A: A: Percent Error =Percent Error = x 100 = x 100 = 4%4%
|200 mL - 208 mL||200 mL - 208 mL|200 mL200 mL