1. Properties of Matter and the Analysis of Glass
Objectives:
Define physical and chemical properties.
List and define the metric system’s basic units and prefixes.
Compare metric and English units: length, volume, and mass.
Define elements and compounds and give examples of each.
State the differences between a solid, liquid, and gas.
Define phase.
State the differences between the wave and particle theories of light.
Describe the dispersion of light through a prism.
Describe the electromagnetic spectrum.
Explain the relationship between color and the selective absorption of light by molecules.
Updated 7/6/2019
Created by C. Ippolito August 2007

2. Properties of Matter and the Analysis of Glass
Objectives:
Distinguish between the Celsius and Fahrenheit temperature scales.
Distinguish mass from weight.
Define density.
Determine the density of irregular-shaped objects.
Define refractive index.
Distinguish crystalline from amorphous solids.
Define double refraction and birefringence.
Describe the flotation and immersion methods for comparing glass specimens.
State how to examine glass fractures to determine the direction of impact for a projectile.
Describe the proper collection of glass evidence.
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Properties of Matter
Physical Properties
describe a substance without reference to any other substance
weight
volume
color
Chemical Properties
describes the behavior of a substance in the presence of another substance
boiling point
melting point
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Created by C. Ippolito August 2007

4. Measuring with SI Units
The International System of Units (SI) is a revised version of the metric system
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Metric Prefixes
are used to increase or decrease base units to a size appropriate for the measurement undertaken
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Metric Units of Length
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Metric Units of Volume
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Metric Units of Mass
Weight – force that measures the pull of gravity on a given mass
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9. Metric Units of Temperature
measure of how hot or cold an object is
Celsius Scale
100 equal intervals between freezing (0°C) and boiling (100°C) points of water
Fahrenheit Scale
1°F is 1/180 change from freezing to boiling
freezing (32°F) and boiling (212°F) points of water
Conversion:
°C = (5/9) x (°F-32)
°F = (1.8 x °C)+32
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Nature of Matter
Matter
anything that has mass and occupies space
Element
matter that cannot be broken down into simpler substances by chemical means
Atom – smallest particle of an element still exhibiting its properties
Compound
matter that can be broken down into simpler substances by chemical means
Molecule – smallest particle of a compound still exhibiting its properties
Periodic Table
systematic arrangement of elements by atomic number
Family – vertical column
Series – horizontal row
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States of Matter
Solid
definite shape
definite volume
particles close together
almost incompressible
Liquid
indefinite shape
particles less close together – “flow”
Gas
indefinite volume
particles separated
compressible
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Changes of State
Freezing/Melting Point
freeze
change from liquid to solid
melt
change from solid to liquid
Boiling/Condensation Point
boil
change from liquid to gas
condense
change from gas to liquid
Sublimation
change from solid directly to gas without passing through liquid state
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Theory of Light
Wave Theory of Light
Amplitude
height from zero to the crest
Wavelength (λ)
distance between crests
SI unit is nanometer
Frequency (ν)
number of wave cycles passing a given point per unit time
SI unit is cycles/sec (cps) or hertz (hz)
Wavelength and frequency are inversely proportional
F = c/λ
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Created by C. Ippolito August 2007

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Behavior of Light
Dispersion
process of separating light into its component colors
Refraction
bending of light as its velocity changes when moving from one medium to another (i.e. air to glass, air to water)
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Created by C. Ippolito August 2007

15. Electromagnetic Spectrum
Visible Light
small part of all “wave” forms of energy
distinguished by wavelengths
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Light as Particles
DeBroglie
hypothesized that waves could act as both particles and waves at different times
Photon
discrete package (particle) of light energy
amount of energy depends on frequency
E = hf h is Planck constant
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Created by C. Ippolito August 2007

17. Physical Properties of Matter
Temperature
amount of heat in a substance
Extensive Properties – change with amount of object
Weight
force of gravity on an object
Mass
amount of matter an object contains
Intensive Properties – same regardless of amount of object
Density
mass per unit volume
Refractive Index
ratio of velocity of light in a vacuum to its velocity in another medium
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Types of Solids
Crystalline Solids
substances whose atoms are arranged in definite geometric patterns
Double Refraction
light refracts into two different beams when crystal does not have cubic configuration
Birefringence – difference between the two refractive indexes
Amorphous Solids
substances whose atoms are arranged in random or disordered positions
glass is actually a “liquid”
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Created by C. Ippolito August 2007

19. Forensic Analysis of Glass
Glass particles can connect a criminal to a crime (Locard’s Principle)
glass from window
glass from headlights
glass from windshield
glass from dinnerware
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Composition of Glass
Sand + metal oxides melted then cooled to form amorphous solid
Float Glass
bottle and window glass
a.k.a. soda (Na2CO3) lime (CaO) glass
Borosilicate Glass
headlights and heat resistant glass (Pyrex)
boron oxide added
Tempered Glass
side and rear car windows – will not shatter
special heating/cooling process
Laminated Glass
car windshield
two glass layers sandwich a layer of plastic
images from mosaik.wordpress.com,
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Created by C. Ippolito August 2007

21. Comparing Glass Fragments
Most glass cannot be individualized using today’s technology based on composition
Physical properties can be used as “class characteristics”:
density
refractive index
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Created by C. Ippolito August 2007

22. Measuring and Comparing Glass Densities
Flotation Method
standard/reference glass particle immersed in liquid
bromoform or bromobenzene added until glass remains suspended
nonstandard particles of similar size and shape added
if suspended density same as standard
sink density greater/float density less
sheet glass can vary by as much as 0.003g/ml but this method can distinguish differences of up to g/ml
so samples likely from same source if density matches
Updated 7/6/2019
Created by C. Ippolito August 2007

23. Determining and Comparing Refractive Indices
Immersion Method
glass particles in liquid medium adjusted by temperature change until its refractive index is equal to that of the glass particle
determined when Becke line disappears
Becke line
halo seen around glass particle when in a liquid with a different refractive index from it’s own
moves toward medium with higher refractive index
GRIM 3
automated system uses computer/video system
images from
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Created by C. Ippolito August 2007

24. Classification of Glass Samples
FBI lab has tabulated density and refractive indices of all glass samples
calculated “distribution” of refractive indices
can correlate data to this to find probability of glass coming from same source
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Glass Fractures
Radial Fracture
cracks in glass that extend out like spokes of a wheel
extend from point of impact
break on side opposite of force
Concentric Fracture
cracks in glass that form a circle around point of impact
break on side where force applied
images from:
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Glass Stress Marks
form arches
perpendicular to side where crack originated
curving until parallel to opposite side
Radial
perpendicular opposite impact point
Concentric
perpendicular on side of impact
3R rule
Radial cracks form Right angle on Reverse side of force
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Created by C. Ippolito August 2007

27. Which bullet hole is first?
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Created by C. Ippolito August 2007