Units of Units of Measurement Measurement Chapter 2 Chapter 2 Section 2 Section 2 Objectives: Objectives: Distinguish between a quantity, a Distinguish between a quantity, a unit, and a measurement standard. unit, and a measurement standard. Name and use SI units for length, Name and use SI units for length, mass, time, volume, and density. mass, time, volume, and density. Distinguish between mass and Distinguish between mass and weight. weight. Perform density calculations. Perform density calculations. Transform a statement of equality Transform a statement of equality into a conversion factor. into a conversion factor.
Transcript
Units of MeasurementUnits of MeasurementChapter 2Chapter 2Section 2Section 2
Objectives:Objectives:Distinguish between a quantity, a unit, Distinguish between a quantity, a unit, and a measurement standard.and a measurement standard.Name and use SI units for length, Name and use SI units for length, mass, time, volume, and density.mass, time, volume, and density.Distinguish between mass and weight.Distinguish between mass and weight.Perform density calculations.Perform density calculations.Transform a statement of equality into Transform a statement of equality into a conversion factor.a conversion factor.
Would you be breaking the Would you be breaking the speed limit in a 40 mi/h zone speed limit in a 40 mi/h zone if you were traveling 60 if you were traveling 60 km/h?km/h?
Measurements are quantitative information.Measurements are quantitative information. Measurements are more than just numbers.Measurements are more than just numbers. Example:Example:
Measurements Measurements representrepresent quantities. quantities. A A quantityquantity is something that has is something that has
magnitude, size, or amount. magnitude, size, or amount. A quantity is not the same thing as A quantity is not the same thing as
measurement.measurement. The quantity represented by a teaspoon is The quantity represented by a teaspoon is
volume.volume. The teaspoon is a unit of measurement, while volume is The teaspoon is a unit of measurement, while volume is
a quantity.a quantity.
SI UnitsSI Units
Scientists use a single measurement Scientists use a single measurement system called system called Le SystLe Systèm èm International d’UnitèsInternational d’Unitès, abbreviated , abbreviated SISI..
SI Units are defined in terms of SI Units are defined in terms of standards of measurement. standards of measurement.
There are seven base units, and There are seven base units, and most other units are derived from most other units are derived from these seven.these seven.
QuantitQuantityy
Quantity Quantity SymbolSymbol
Unit Unit NameName
Unit Unit
Abbrev.Abbrev.Defined standardDefined standard
LengtLengthh
ll MeterMeter mm The length of the The length of the path traveled by path traveled by light in a vacuum light in a vacuum during a time during a time interval of 1/299 interval of 1/299 792 458 of a 792 458 of a second.second.
MassMass mm KilograKilogramm
kgkg Unit of mass equal Unit of mass equal to the mass of the to the mass of the international international prototype.prototype.
TimeTime tt SecondSecond ss Duration of 9 192 Duration of 9 192 631 770 periods of 631 770 periods of the radiation the radiation corresponding to corresponding to the transition the transition between the two between the two hyperfine levels of hyperfine levels of the ground state of the ground state of the cesium-133 the cesium-133 atom.atom.
QuantityQuantity QuantitQuantity Namey Name
Unit Unit NameName
Unit Unit AbbrevAbbrev
..
Defined Defined StandardStandard
TemperatuTemperaturere
TT kelvinkelvin KK The fraction The fraction 1/273.16 of 1/273.16 of the the thermodynamithermodynamic temperature c temperature of the triple of the triple point of water.point of water.
Amount Amount of of
SubstancSubstancee
nn molemole molmol The amount of The amount of substance of a substance of a system which system which contains as contains as many many elementary elementary entities as entities as there are there are atoms in 0.012 atoms in 0.012 kilogram of kilogram of carbon-12.carbon-12.
Quantity
Quantity Symbol
Unit Name
Unit Abbrev
.
Defined Statement
Electric Current
I ampere A The constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2x10-7 newton per meter of length.
Luminous
Intensity
Iv Candela Cd The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540x1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
SI Base Units (LENGTH)SI Base Units (LENGTH)
The SI unit for length is the meter (m).The SI unit for length is the meter (m). A distance of 1 m is about the width of A distance of 1 m is about the width of
an average doorway.an average doorway. Longer distances can be expressed Longer distances can be expressed
using the kilometer, km. One km using the kilometer, km. One km equals 1000m.equals 1000m.
For shorter distances, the centimeter For shorter distances, the centimeter is often used.is often used.
SI Base Units (MASS)SI Base Units (MASS) Mass is a measure of the quantity of Mass is a measure of the quantity of
matter.matter. The SI standard unit is the kilogram (kg).The SI standard unit is the kilogram (kg). The mass of typical textbook is 1 kg. The mass of typical textbook is 1 kg.
The gram (g), which is 1/1000 of a The gram (g), which is 1/1000 of a kilogram, is more useful for measuring kilogram, is more useful for measuring masses of small objects, such as flasks masses of small objects, such as flasks and beakers.and beakers.
Mass is often confused with weight.Mass is often confused with weight. Weight is a measure of the gravitational pull Weight is a measure of the gravitational pull
on matter.on matter. Mass does not depend on gravity.Mass does not depend on gravity.
Using the SI Prefix ChartUsing the SI Prefix Chart SI prefixes are based on powers of 10.SI prefixes are based on powers of 10. To change between one prefix to another To change between one prefix to another
requires the decimal point to be moved in requires the decimal point to be moved in either direction.either direction.
For example: Convert 4.0 km into cm.For example: Convert 4.0 km into cm. 11stst put your finger on the km space. Count how many put your finger on the km space. Count how many
spaces it takes to get to centimeters.spaces it takes to get to centimeters. Move your decimal point this many spaces.Move your decimal point this many spaces.
If you are counting spaces from left to right, the If you are counting spaces from left to right, the decimal point is moved to from left to right. (The decimal point is moved to from left to right. (The number should get bigger.)number should get bigger.)
If you are counting spaces from right to left, the If you are counting spaces from right to left, the decimal point is moved from right to left. (The decimal point is moved from right to left. (The number should get smaller.)number should get smaller.)
4.0 km = 400 000. cm4.0 km = 400 000. cm
SI PrefixesSI Prefixes
SI PrefixesSI Prefixes
Complete the following conversions.Complete the following conversions.
Derived SI UnitsDerived SI Units Many SI units are combinations of the Many SI units are combinations of the
quantities shown in the first table.quantities shown in the first table. Combinations of SI base units form Combinations of SI base units form
derived unitsderived units.. Derived units are produced by Derived units are produced by
multiplying or dividing standard units. multiplying or dividing standard units. For example, area, a derived unit, is For example, area, a derived unit, is length times width. length times width. If both length and width are expressed in If both length and width are expressed in
meters, the area unit equals meters times meters, the area unit equals meters times meters, which is square meters, meters, which is square meters, abbreviated mabbreviated m22..
Derived SI UnitsQuantity Quantit
y Symbol
Unit Unit Abbr
.
Derivation
Area A square meter
m2 length x width
Volume V cubic meter m3 length x width x height
Density D kilograms per cubic
meter
kg m3
mass/volume
Molar mass
M kilograms per mol
kg mol
mass/amount of
substance
Molar volume
Vm cubic meters per mol
m3
mol
volume/amount
of substance
Energy E Joule J force x length
Derived Units (VOLUME)Derived Units (VOLUME) VolumeVolume is the amount of space occupied is the amount of space occupied
by an object.by an object. The derived SI unit is cubic meters, mThe derived SI unit is cubic meters, m33. .
One cubic meter is equal to the volume of a One cubic meter is equal to the volume of a cube who edges are 1 m long.cube who edges are 1 m long.
Chemists measure the volumes of liquids Chemists measure the volumes of liquids and gases using the non-SI unit liter (L).and gases using the non-SI unit liter (L).
1 L = 1000 cm1 L = 1000 cm33
Another non-SI unit is the milliliter, mL and Another non-SI unit is the milliliter, mL and it is used for smaller volumes.it is used for smaller volumes.
1000 mL = 1L = 1000 cm1000 mL = 1L = 1000 cm33
Derived Units (DENSITY)Derived Units (DENSITY)
Density is the ratio of mass to volume, or mass divided by volume
Mathematically it is written as:density = mass or D = m
volume V The SI unit for Density is kg/m3 or g/cm3 for
small density measurements.
m
D V
DensityDensity
Density is a characteristic physical property of a substance.
It does not depend on the sample size because as the sample’s mass increases its volume increases proportionately, and the ratio is constant. Density can be used to identify a
substance.
Density ProblemsDensity Problems
A sample of aluminum metal has a mass A sample of aluminum metal has a mass of of
8.4 g. The volume of the sample is 3.1 8.4 g. The volume of the sample is 3.1 cmcm33..
Calculate the density of aluminum.Calculate the density of aluminum.
Solution: Solution: Given: mass (m) = 8.4gGiven: mass (m) = 8.4g
volume (volume (VV ) = 3.1 cm ) = 3.1 cm33
Unknown: density (Unknown: density (DD ) )
density = density = mass mass = = 8.4g 8.4g = 2.7 = 2.7 g/cmg/cm33
volume 3.1cmvolume 3.1cm33
Density ProblemsDensity Problems
What is the density of a block of marble What is the density of a block of marble thatthat
occupies 310. cmoccupies 310. cm33 and has a mass of 853 and has a mass of 853 g?g?
