Ch 2 Section 2 Flashcards
Measurements represent
Quantities
A quantity is something that has
Magnitude, size, or amount
Quantity is not the same as a
Measurement
Units of measurement compare
What is to be measured with a previously defined size
Nearly every measurement is a
Number plus a unit with choice of unit depending on quantity being measured
SI
Le systéme international d’Unités
Measurement system agreed on by scientists all over the world
SI system adopted in
1960 by General Conference on weights and measures
SI has
7 base units with most other units derived from these 7
SI units are defined in terms of
Standards of measurement
Standards are objects or natural phenomena that are of
Constant value
Easy to preserve and reproduce
Practical on size
Numbers are written in a form that is
Agreed upon internationally
Prefixes added to names of SI units represent
Quantities that are larger or smaller than the base units
Centi
1/100
1 cm
1/100 of a meter
SI standard unit for mass is
Kilogram
Gram
1/1000 of a kg
Gram is more
Useful for measuring masses of Small objects
For even smaller objects (measuring mass)
Milligram is used
1 mg
1/1000 of a gram
Mass is determined by
Comparing mass of an object with a set of standard masses that are part of the balance
Measurements are
Quantitative information.
Weight is a measure of the
Gravitational pull on matter
Weight is typically measured on a
Spring scale
As the force of gravity on an object increases
Weight increases
SI standard unit for length is
Meyer
1 km
1000 m
To express shorter distances the
Cm is often used
Combinations of SI units form
Derived units
Derived units are produced by
Multiplying or dividing standard units
Pascal
kg/ m x s^2
Prefixed can also be added to express
Derived units
Volume is the amount of
Space occupied by an object
Derived SI unit of volume is
m^3
One m^3=
Volume of a cube whose edges are 1 m long
The cm^3 is often used to
Express the volume of materials in a chem lab
m^3=
1000000 cm^3
When chemists measures volumes of liquids and gases they often use
A non SI unit called the liter
Liter=
1 decimeter cubed
1 liter =
1000 cm cubed
1000 mL=
1 L
mL and cm^3 are
Interchangeable
Density
Ratio of mass to volume
Mass/volume
SI unit for density is derived from
Base units for mass and volume- kg and m^3- and can be expressed as
kg/m^3
Density is often expressed as
g/ cm^3 it g/mL
Densities of gas are generally expressed as
kg/m^3 or g/L
Density is a characteristic
Physical property of a substance
Density doesn’t depend on the size of the same because
As the samples mass increases, it’s volume increases proportionately, and the ratio of mass to volume is constant
Density can be used as
A property to help identify a substance
Density varies with
Temperature
Most objects expand as temperature increases thereby
Increasing in volume
Density usually
Decreases with increasing temperature
A conversion factor is a
Ratio derived from the equality between two different units that can be used to convert from one unit to the other
Each conversion factor equals 1 because the
2 quantities divided in any conversion factor are equivalent to each other
Because conversion factors are equal to 1 they can be multiplied by other factors in equations
Without changing the validity of the equations
Dimensional analysis
Mathematical technique that allows you to use units to solve problems involving measurements
Quantity sought =
Quantity given x conversion factor
It is always best to begin with an idea
Of the units you will need in your final answer
Conversion factors can be derived if you know the
Relationship between the unit you have and the unit you want
1 m
10 decimeters
