Podcast
Questions and Answers
Glass is a hard, amorphous material made by melting sand, lime (also called calcium oxide), and sodium oxide at very high temperatures.
Glass is a hard, amorphous material made by melting sand, lime (also called calcium oxide), and sodium oxide at very high temperatures.
True (A)
The primary ingredient of glass is carbon dioxide.
The primary ingredient of glass is carbon dioxide.
False (B)
Glass is called an amphibious solid because its atoms are arranged in a random fashion.
Glass is called an amphibious solid because its atoms are arranged in a random fashion.
False (B)
Fine glassware and decorative art glass, called crystal or leaded glass, contain lead oxide rather than calcium oxide.
Fine glassware and decorative art glass, called crystal or leaded glass, contain lead oxide rather than calcium oxide.
Each type of glass has a density that is specific to that glass. One method of matching glass fragments is by a density comparison.
Each type of glass has a density that is specific to that glass. One method of matching glass fragments is by a density comparison.
Density of glass is calculated by dividing the:
Density of glass is calculated by dividing the:
The refractive index is a tool used to study how light bends as it passes through:
The refractive index is a tool used to study how light bends as it passes through:
When light travels through any medium other than a vacuum, the particles in that medium slow the light down. As the density of the medium increases, the speed of light passing through that material _____.
When light travels through any medium other than a vacuum, the particles in that medium slow the light down. As the density of the medium increases, the speed of light passing through that material _____.
The speed of light passing through air is slightly:
The speed of light passing through air is slightly:
What is Snell's law?
What is Snell's law?
One method of determining if the evidence glass matches the glass from the crime scene is to compare the:
One method of determining if the evidence glass matches the glass from the crime scene is to compare the:
The submersion method involves placing the glass fragment into different liquids of known refractive indexes. If a piece of glass and a liquid have the same refractive index, the glass fragment will seem:
The submersion method involves placing the glass fragment into different liquids of known refractive indexes. If a piece of glass and a liquid have the same refractive index, the glass fragment will seem:
If the refractive indexes of several different liquids are known, the:
If the refractive indexes of several different liquids are known, the:
If the refractive index of the liquid medium is different than the refractive index of the piece of glass, a halo-like ring appears around the edge of the glass. This halo-like effect is called a:
If the refractive index of the liquid medium is different than the refractive index of the piece of glass, a halo-like ring appears around the edge of the glass. This halo-like effect is called a:
Obsidian refers to:
Obsidian refers to:
When glass is hit:
When glass is hit:
By examining glass fracture patterns, it is:
By examining glass fracture patterns, it is:
Silicon dioxide is:
Silicon dioxide is:
Glass will break first on the weaker side, the side:
Glass will break first on the weaker side, the side:
As a bullet passes through glass, it pushes some glass ahead of it, causing a cone-shaped piece of glass to exit along with the bullet. The cone of glass makes the exit hole:
As a bullet passes through glass, it pushes some glass ahead of it, causing a cone-shaped piece of glass to exit along with the bullet. The cone of glass makes the exit hole:
If several shots are fired through glass, the _____ in which the shots were fired can be determined if enough of the glass is available or can be reconstructed.
If several shots are fired through glass, the _____ in which the shots were fired can be determined if enough of the glass is available or can be reconstructed.
The angle at which a bullet enters a piece of window glass can help locate the position of the shooter. If the bullet was fired perpendicular to the windowpane, the entry hole of the bullet will be _____.
The angle at which a bullet enters a piece of window glass can help locate the position of the shooter. If the bullet was fired perpendicular to the windowpane, the entry hole of the bullet will be _____.
A high-speed bullet fired from a great distance will often exhibit characteristics of a _____ fired from a closer range.
A high-speed bullet fired from a great distance will often exhibit characteristics of a _____ fired from a closer range.
_____ is a combination of two or more types of glass, one hard and one soft. The softer layer makes the glass more elastic so it can flex instead of shatter.
_____ is a combination of two or more types of glass, one hard and one soft. The softer layer makes the glass more elastic so it can flex instead of shatter.
_____ is also known as tempered glass. It is used in windshields and is composed of two layers of glass bonded together by a layer of plastic in the middle.
_____ is also known as tempered glass. It is used in windshields and is composed of two layers of glass bonded together by a layer of plastic in the middle.
How is the density of glass calculated?
How is the density of glass calculated?
The refractive index is a tool used to study how light bends as it passes through what?
The refractive index is a tool used to study how light bends as it passes through what?
When light travels through any medium other than a vacuum, the particles in that medium slow the light down. As the density of the medium increases, what happens to the speed of light passing through that material?
When light travels through any medium other than a vacuum, the particles in that medium slow the light down. As the density of the medium increases, what happens to the speed of light passing through that material?
How does the speed of light passing through air compare to the speed of light passing through a vacuum?
How does the speed of light passing through air compare to the speed of light passing through a vacuum?
What does Snell's law describe?
What does Snell's law describe?
In the submersion method, what happens if a piece of glass and a liquid have the same refractive index?
In the submersion method, what happens if a piece of glass and a liquid have the same refractive index?
If the refractive indexes of several different liquids are known, what can the submersion method be used to estimate?
If the refractive indexes of several different liquids are known, what can the submersion method be used to estimate?
If the refractive index of the liquid medium is different than the refractive index of the piece of glass, a halo-like ring appears around the edge of the glass. What is this halo-like effect called?
If the refractive index of the liquid medium is different than the refractive index of the piece of glass, a halo-like ring appears around the edge of the glass. What is this halo-like effect called?
What does obsidian refer to?
What does obsidian refer to?
What can happen to glass when it is hit?
What can happen to glass when it is hit?
What is possible to determine by examining glass fracture patterns?
What is possible to determine by examining glass fracture patterns?
What is the chemical name for silica?
What is the chemical name for silica?
Glass will break first on the weaker side, which is which side relative to the strike? What type of fractures will result?
Glass will break first on the weaker side, which is which side relative to the strike? What type of fractures will result?
As a bullet passes through glass, it pushes some glass ahead of it, causing a cone-shaped piece of glass to exit along with the bullet. How does this affect the exit hole compared to the entrance hole?
As a bullet passes through glass, it pushes some glass ahead of it, causing a cone-shaped piece of glass to exit along with the bullet. How does this affect the exit hole compared to the entrance hole?
When light travels through any medium other than a vacuum, the particles in that medium slow the light down. As the density of the medium increases, the:
When light travels through any medium other than a vacuum, the particles in that medium slow the light down. As the density of the medium increases, the:
What materials are used to create soda lime glass?
What materials are used to create soda lime glass?
Can glass be considered trace evidence?
Can glass be considered trace evidence?
What is the primary ingredient in glass?
What is the primary ingredient in glass?
What is sodium oxide used for in glass production?
What is sodium oxide used for in glass production?
What is the role of calcium oxide in glass production?
What is the role of calcium oxide in glass production?
What are crystalline solids?
What are crystalline solids?
What are amorphous solids?
What are amorphous solids?
Is glass crystalline or amorphous?
Is glass crystalline or amorphous?
How does glass break?
How does glass break?
What is soda lime glass?
What is soda lime glass?
What effect does adding different metal oxides have on glass?
What effect does adding different metal oxides have on glass?
What characteristics of glass allow for comparisons in forensic analysis?
What characteristics of glass allow for comparisons in forensic analysis?
What is the formula for calculating density?
What is the formula for calculating density?
How is mass typically measured in a lab setting for density determination?
How is mass typically measured in a lab setting for density determination?
How can the volume of an irregular glass fragment be measured?
How can the volume of an irregular glass fragment be measured?
What is the refractive index?
What is the refractive index?
Define refractive index in the context of forensic analysis.
Define refractive index in the context of forensic analysis.
What is the normal line in the context of light refraction?
What is the normal line in the context of light refraction?
What happens to light when it moves from a less dense medium to a more dense medium?
What happens to light when it moves from a less dense medium to a more dense medium?
What does the term refraction mean?
What does the term refraction mean?
What happens to light when it moves from a more dense medium to a less dense medium?
What happens to light when it moves from a more dense medium to a less dense medium?
What is the submersion method used for in glass analysis?
What is the submersion method used for in glass analysis?
How is the refractive index practically applied in comparing glass fragments using the submersion method?
How is the refractive index practically applied in comparing glass fragments using the submersion method?
What is a Becke line and what does it indicate?
What is a Becke line and what does it indicate?
Provide examples of glass commonly found at crime scenes.
Provide examples of glass commonly found at crime scenes.
Why is the location of the Becke line significant when comparing refractive indices?
Why is the location of the Becke line significant when comparing refractive indices?
What happens when glass is forced to stretch beyond its elastic limit?
What happens when glass is forced to stretch beyond its elastic limit?
What type of fracture typically occurs first when glass breaks due to impact?
What type of fracture typically occurs first when glass breaks due to impact?
What are radial fractures?
What are radial fractures?
What information can glass fracture patterns provide to investigators?
What information can glass fracture patterns provide to investigators?
Why doesn't glass break into regular pieces?
Why doesn't glass break into regular pieces?
What are secondary fractures in glass, and where do they occur?
What are secondary fractures in glass, and where do they occur?
How does glass behave on the side it is impacted?
How does glass behave on the side it is impacted?
What are concentric fractures in glass?
What are concentric fractures in glass?
Describe the forces acting on glass when it is hit by an object like a rock or bullet.
Describe the forces acting on glass when it is hit by an object like a rock or bullet.
Which type of fractures appear first when glass is impacted?
Which type of fractures appear first when glass is impacted?
Describe what happens as a bullet passes through glass.
Describe what happens as a bullet passes through glass.
How does the exit side of a bullet hole in glass typically compare to the entrance side?
How does the exit side of a bullet hole in glass typically compare to the entrance side?
How does the entrance side of a bullet hole in glass typically appear?
How does the entrance side of a bullet hole in glass typically appear?
How do radiating fracture lines from a subsequent shot interact with existing fracture lines?
How do radiating fracture lines from a subsequent shot interact with existing fracture lines?
Under what condition can the sequence of shots fired through glass be determined?
Under what condition can the sequence of shots fired through glass be determined?
What is tempered glass, and where is it commonly used?
What is tempered glass, and where is it commonly used?
What is safety glass (laminated glass), and where is it commonly used?
What is safety glass (laminated glass), and where is it commonly used?
What evidence related to window glass can help locate the position of a shooter?
What evidence related to window glass can help locate the position of a shooter?
How can glass fragments become trace evidence related to a shooter?
How can glass fragments become trace evidence related to a shooter?
Describe the composition of bulletproof glass.
Describe the composition of bulletproof glass.
Describe the shape of a bullet hole in glass for different impact angles.
Describe the shape of a bullet hole in glass for different impact angles.
What is the relationship between the incident angle and the reflected angle when light hits a surface?
What is the relationship between the incident angle and the reflected angle when light hits a surface?
What type of property is density?
What type of property is density?
Is density an intensive or extensive property?
Is density an intensive or extensive property?
What does it mean for a property to be intensive?
What does it mean for a property to be intensive?
What is a common unit for density, particularly for liquids or relating volume by displacement?
What is a common unit for density, particularly for liquids or relating volume by displacement?
If the volume of an object increases while its mass stays the same, what happens to its numerical value of density?
If the volume of an object increases while its mass stays the same, what happens to its numerical value of density?
What is another common unit for density, often used for solids when dimensions are measured?
What is another common unit for density, often used for solids when dimensions are measured?
What property of a material is the refractive index primarily dependent upon?
What property of a material is the refractive index primarily dependent upon?
What happens to light passing between two mediums if it strikes the interface perpendicularly (at a 0° angle to the normal)?
What happens to light passing between two mediums if it strikes the interface perpendicularly (at a 0° angle to the normal)?
Glass can be considered trace evidence.
Glass can be considered trace evidence.
What is sodium oxide ($Na_2O$) used for in glassmaking?
What is sodium oxide ($Na_2O$) used for in glassmaking?
What is the role of calcium oxide ($CaO$) in glassmaking?
What is the role of calcium oxide ($CaO$) in glassmaking?
What property characterizes crystalline solids?
What property characterizes crystalline solids?
What property characterizes amorphous solids?
What property characterizes amorphous solids?
How does glass typically break?
How does glass typically break?
What is soda lime glass often used for?
What is soda lime glass often used for?
What characteristics allow forensic comparisons between glass fragments?
What characteristics allow forensic comparisons between glass fragments?
How is mass typically measured when determining the density of a glass fragment?
How is mass typically measured when determining the density of a glass fragment?
How is the volume of an irregular glass fragment typically measured?
How is the volume of an irregular glass fragment typically measured?
What is the normal line in optics?
What is the normal line in optics?
When light moves from a less dense medium to a more optically dense medium, how does its speed and direction change?
When light moves from a less dense medium to a more optically dense medium, how does its speed and direction change?
Define refraction.
Define refraction.
When light moves from a more optically dense medium to a less dense medium, how does its speed and direction change?
When light moves from a more optically dense medium to a less dense medium, how does its speed and direction change?
When is the submersion method particularly useful in forensic glass analysis?
When is the submersion method particularly useful in forensic glass analysis?
How does the submersion method work to determine refractive index?
How does the submersion method work to determine refractive index?
What is a Becke line and how is it used?
What is a Becke line and how is it used?
What are common examples of glass evidence found at crime scenes?
What are common examples of glass evidence found at crime scenes?
Why is the location of the Becke line significant?
Why is the location of the Becke line significant?
What happens when glass is stressed beyond its elastic limit?
What happens when glass is stressed beyond its elastic limit?
What information can be inferred from glass fracture patterns?
What information can be inferred from glass fracture patterns?
Why doesn't glass break into regular, predictable pieces?
Why doesn't glass break into regular, predictable pieces?
What are concentric fractures?
What are concentric fractures?
What happens to the side of glass that is hit during an impact?
What happens to the side of glass that is hit during an impact?
What happens to the side of glass opposite the point of impact?
What happens to the side of glass opposite the point of impact?
What often happens as a high-velocity projectile like a bullet passes through glass?
What often happens as a high-velocity projectile like a bullet passes through glass?
How can the sequence of multiple impacts (e.g., bullet holes) on glass be determined?
How can the sequence of multiple impacts (e.g., bullet holes) on glass be determined?
What is tempered glass?
What is tempered glass?
What is laminated safety glass?
What is laminated safety glass?
What aspect of a bullet hole in a window can help locate the shooter's position?
What aspect of a bullet hole in a window can help locate the shooter's position?
How can breaking glass create trace evidence relevant to the person causing the break?
How can breaking glass create trace evidence relevant to the person causing the break?
Describe the typical structure of bullet-resistant glass.
Describe the typical structure of bullet-resistant glass.
How does the shape of a bullet hole relate to the angle of impact?
How does the shape of a bullet hole relate to the angle of impact?
What is the relationship between the angle of incidence and the angle of reflection?
What is the relationship between the angle of incidence and the angle of reflection?
Is density a physical or chemical property?
Is density a physical or chemical property?
What defines an intensive property?
What defines an intensive property?
What is a common unit for density?
What is a common unit for density?
If the volume of an object increases while its mass remains constant, what happens to its density?
If the volume of an object increases while its mass remains constant, what happens to its density?
What physical property is the refractive index closely related to?
What physical property is the refractive index closely related to?
Does light bend if it enters a new medium perpendicular to the surface (along the normal)?
Does light bend if it enters a new medium perpendicular to the surface (along the normal)?
What characterizes crystalline solids?
What characterizes crystalline solids?
What characterizes amorphous solids?
What characterizes amorphous solids?
Is glass considered crystalline or amorphous?
Is glass considered crystalline or amorphous?
What characteristics of glass allow for forensic comparisons?
What characteristics of glass allow for forensic comparisons?
How is mass typically measured in a laboratory setting?
How is mass typically measured in a laboratory setting?
How can the volume of an irregular object like a glass fragment be measured?
How can the volume of an irregular object like a glass fragment be measured?
What happens to light when it moves from one medium into another, relating to the refractive index?
What happens to light when it moves from one medium into another, relating to the refractive index?
What is the refractive index a measure of?
What is the refractive index a measure of?
What is the "normal line" in the context of refraction?
What is the "normal line" in the context of refraction?
What happens to light when it moves from a less dense medium to a more optically dense medium?
What happens to light when it moves from a less dense medium to a more optically dense medium?
What does "refraction" mean in the context of light?
What does "refraction" mean in the context of light?
What happens to light when it moves from a more optically dense medium to a less dense medium?
What happens to light when it moves from a more optically dense medium to a less dense medium?
When is the submersion method typically used in glass analysis?
When is the submersion method typically used in glass analysis?
How is the refractive index applied in the submersion method?
How is the refractive index applied in the submersion method?
What is a Becke line?
What is a Becke line?
Why is the location and movement of the Becke line significant during refractive index analysis?
Why is the location and movement of the Becke line significant during refractive index analysis?
What is a primary type of fracture pattern in broken glass?
What is a primary type of fracture pattern in broken glass?
What are radial fractures and where do they originate?
What are radial fractures and where do they originate?
What clues can glass fracture patterns provide to investigators?
What clues can glass fracture patterns provide to investigators?
Why doesn't glass typically break into regular, predictable pieces?
Why doesn't glass typically break into regular, predictable pieces?
What are secondary fractures in glass often called, and where do they form?
What are secondary fractures in glass often called, and where do they form?
What happens to the side of the glass that is impacted?
What happens to the side of the glass that is impacted?
Describe concentric fractures in glass.
Describe concentric fractures in glass.
When an object like a rock or bullet hits glass, what forces act on each side?
When an object like a rock or bullet hits glass, what forces act on each side?
Which type of glass fracture appears first upon impact?
Which type of glass fracture appears first upon impact?
What typically happens as a bullet passes through glass?
What typically happens as a bullet passes through glass?
How does the exit side of a bullet hole in glass compare to the entrance side?
How does the exit side of a bullet hole in glass compare to the entrance side?
Is the entrance hole of a bullet in glass smaller or larger than the exit hole?
Is the entrance hole of a bullet in glass smaller or larger than the exit hole?
What happens to radiating fracture lines from a subsequent bullet shot when they encounter existing fracture lines?
What happens to radiating fracture lines from a subsequent bullet shot when they encounter existing fracture lines?
How can the order of multiple shots fired through glass be determined?
How can the order of multiple shots fired through glass be determined?
What is tempered glass and how is it made?
What is tempered glass and how is it made?
What evidence in broken window glass can help locate the position of a shooter?
What evidence in broken window glass can help locate the position of a shooter?
How can breaking glass create trace evidence relevant to a shooter or person causing the impact?
How can breaking glass create trace evidence relevant to a shooter or person causing the impact?
Describe the composition of typical bullet-resistant glass.
Describe the composition of typical bullet-resistant glass.
What shape is a bullet hole in glass if the impact is perpendicular? What if the angle is oblique?
What shape is a bullet hole in glass if the impact is perpendicular? What if the angle is oblique?
According to the law of reflection, how does the angle of incidence relate to the angle of reflection?
According to the law of reflection, how does the angle of incidence relate to the angle of reflection?
What is a common unit for density relevant to forensic glass analysis?
What is a common unit for density relevant to forensic glass analysis?
If the mass of an object remains constant but its volume increases, what happens to its density?
If the mass of an object remains constant but its volume increases, what happens to its density?
Flashcards
What is glass?
What is glass?
A hard, amorphous material made by melting sand, lime (calcium oxide), and sodium oxide at high temperatures.
Is carbon dioxide the primary ingredient of glass?
Is carbon dioxide the primary ingredient of glass?
False. The primary ingredient of glass is silicon dioxide (SiO2) or silica, derived from sand.
Is glass an 'amphibious' solid with ordered atoms?
Is glass an 'amphibious' solid with ordered atoms?
False; glass is called an amorphous solid because its atoms are arranged randomly, not in a crystalline structure.
Does fine glassware contain lead oxide?
Does fine glassware contain lead oxide?
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Is density comparison used to match glass fragments?
Is density comparison used to match glass fragments?
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How is density calculated?
How is density calculated?
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What is refractive index?
What is refractive index?
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How does density affect light speed?
How does density affect light speed?
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Is light faster in air or a vacuum?
Is light faster in air or a vacuum?
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What is Snell's Law?
What is Snell's Law?
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How to match glass fragments?
How to match glass fragments?
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What happens when glass matches liquid's refractive index?
What happens when glass matches liquid's refractive index?
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What can be estimated using the submersion method?
What can be estimated using the submersion method?
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What is the halo-like ring called?
What is the halo-like ring called?
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What is obsidian?
What is obsidian?
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What happens when glass is hit?
What happens when glass is hit?
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What can be determined by examining glass fracture patterns?
What can be determined by examining glass fracture patterns?
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What is silicon dioxide?
What is silicon dioxide?
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Where does glass break first?
Where does glass break first?
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Is the exit hole larger than the entrance hole?
Is the exit hole larger than the entrance hole?
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What can be determined from multiple shots through glass?
What can be determined from multiple shots through glass?
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What shape will the bullet entry hole be if fired perpendicularly?
What shape will the bullet entry hole be if fired perpendicularly?
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What characteristics will a high-speed bullet exhibit from a great distance?
What characteristics will a high-speed bullet exhibit from a great distance?
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What type of glass is a combination of two or more other glasses?
What type of glass is a combination of two or more other glasses?
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What kind of glass is used in windshields?
What kind of glass is used in windshields?
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Soda Lime Glass Ingredients
Soda Lime Glass Ingredients
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Glass as Trace Evidence?
Glass as Trace Evidence?
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Primary Glass Ingredient
Primary Glass Ingredient
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Sodium Oxide's Role in Glass
Sodium Oxide's Role in Glass
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Calcium Oxide's Role in Glass
Calcium Oxide's Role in Glass
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Crystalline Solids
Crystalline Solids
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Amorphous Solids
Amorphous Solids
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Glass: Crystalline or Amorphous?
Glass: Crystalline or Amorphous?
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How Glass Breaks
How Glass Breaks
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Soda-Lime Glass
Soda-Lime Glass
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Metal Oxides in Glass
Metal Oxides in Glass
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Glass Comparison Factors
Glass Comparison Factors
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Density Formula
Density Formula
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Measuring Mass
Measuring Mass
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Measuring Volume
Measuring Volume
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Refractive Index
Refractive Index
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Refractive Index (Definition)
Refractive Index (Definition)
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Normal Line
Normal Line
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Light: Less Dense to More Dense
Light: Less Dense to More Dense
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Refraction
Refraction
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Light: More Dense to Less Dense
Light: More Dense to Less Dense
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Submersion Method
Submersion Method
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Applying Refractive Index
Applying Refractive Index
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Becke Line
Becke Line
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Glass at Crime Scenes
Glass at Crime Scenes
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Becke Line Significance
Becke Line Significance
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Glass Stretching
Glass Stretching
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Glass Break Types
Glass Break Types
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Radial Fractures
Radial Fractures
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Fracture Pattern Clues
Fracture Pattern Clues
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Why Glass Doesn't Break Regularly
Why Glass Doesn't Break Regularly
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Secondary Fractures
Secondary Fractures
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Impacted Glass
Impacted Glass
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Concentric Glass
Concentric Glass
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Rock/Bullet Hitting Glass
Rock/Bullet Hitting Glass
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First Fractures to Appear
First Fractures to Appear
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Bullet Through Glass
Bullet Through Glass
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Exit Side of Hole
Exit Side of Hole
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Entrance
Entrance
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Subsequent Shot Fracture Lines
Subsequent Shot Fracture Lines
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Determining Shot Order
Determining Shot Order
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Tempered Glass
Tempered Glass
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Safety Glass
Safety Glass
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Locating the Shooter
Locating the Shooter
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Backscatter
Backscatter
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Bulletproof Glass
Bulletproof Glass
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Bullet Entry
Bullet Entry
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Incident vs. Reflected Angle
Incident vs. Reflected Angle
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Density Property Type
Density Property Type
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Density: Intensive or Extensive?
Density: Intensive or Extensive?
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Intensive (Property)
Intensive (Property)
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Density Unit
Density Unit
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Increasing Volume's Impact on Density
Increasing Volume's Impact on Density
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Object Volume Unit
Object Volume Unit
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Refraction Index Dependence
Refraction Index Dependence
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Light w/out Angle
Light w/out Angle
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Study Notes
- Glass is a hard, amorphous material.
- Glass is created by melting sand, lime (calcium oxide), and sodium oxide at very high temperatures.
- The primary ingredient of glass is not carbon dioxide
- Glass is not called an amphibious solid
- Crystal or leaded glass contains lead oxide rather than calcium oxide.
- Each type of glass has a specific density.
- Matching glass fragments can be done by density comparison.
- Depending on the size, glass can be trace evidence.
Materials to create soda-lime glass
- Silica, sodium oxide, and calcium oxide are used
Role of Silica/Silicon Dioxide (Primary Ingredient)
- The primary ingredient in glass is silica/silicon dioxide.
Role of Sodium Oxide
- Sodium oxide reduces the temperature of silica so it melts sooner.
Role of Calcium Oxide
- Calcium oxide prevents glass from being soluble in water.
Crystalline vs Amorphous Solids
- Crystalline solids have a regular atomic structure.
- Amorphous solids have an irregular atomic structure.
- Glass is amorphous.
- Glass breaks in a variety of irregular fracture patterns because it is amorphous.
Soda-Lime Glass
- Soda-lime glass is inexpensive and is used for most glass containers.
Adding Different Metal Oxides
- Adding different metal oxides yields different colors and characteristics allowing comparisons, such as densities and refractive indexes.
Density
- Density is calculated by dividing the mass of a substance by its volume.
- d=m/v is a formula for calculating density
- Mass is measured with a balance beam in grams
- Volume is measured by placing the glass fragment into a beaker filled with water and measuring the overflow in millimeters.
- The density numerical value decreases if the volume of an object increases.
- g/mL is the unit for density
- The volume of an object is g/cm^3
- Density is a physical property.
- Density is intensive which means it doesn't change if it is broken or a part of the sample is taken away
Refractive Index
- Refractive index studies how light bends as it passes through one substance into another.
- The refractive index is dependent upon the density of the material.
- As the density of a medium increases, the speed of light passing through it decreases.
- Light travels slower through air than a vacuum because air is denser.
- Snell's law describes the behavior of light as it travels from one medium to another.
- Comparing the refractive index of evidence glass to the refractive index of glass from the crime scene can help determine if they match.
- Refraction occurs when a beam of light moves from one medium into another, the speed changes, and the direction bends.
- Refraction is the bend
- Without an angle, there is no bend
- The normal line is perpendicular to the glass surface, where the two mediums meet.
- When light travels from a less dense medium to a more dense medium, the speed slows, and bends light towards the normal line.
- When light travels from a more dense medium to a less dense medium the speed goes up, and bends light away from the normal line
- The incident vs reflected angle are the same.
Submersion Method
- The submersion method involves placing a glass fragment into liquids with known refractive indexes.
- The submersion method is used when glass fragments found at the crime scene are small.
- Glass seems to disappear when placed in a liquid with the same refractive index.
- The submersion method can estimate the refractive index of glass if the refractive indexes of several liquids are known.
- A Becke line is a halo-like ring that appears around the edge of glass when the refractive index of the liquid medium is different than that of the glass.
- Applying the refractive index, the glass fragments will disappear when placed in a liquid of the same refractive index
- A Becke line is a halo like effect appearing at the edges of a glass fragment when the reflective index of the glass and liquid are different.
- If the line is inside the glass perimeter, the glass index is higher than the index of the liquid; if the line is outside the glass perimeter, the glass index is lower.
- The location of the becke line is significant because it is located in the medium with the higher index; located on the outside=refractive index is higher for the medium
Additional Information
- Obsidian is volcanic glass.
- Examples of glass used in crime scenes, are glass fragments from headlights or broken car windows
- Glass can stretch slightly when hit.
- Examining glass fracture patterns allows for the determination of which side of the glass was hit.
- Silicon dioxide is the chemical name for silica.
- Glass breaks first on the side opposite the strike, resulting in radial fractures.
- Fracture lines appear when glass is forced to stretch too far.
- What kind of breaks does glass have? Radial fracture
- Radial fractures occur on the opposite side and radiate out
- Fracture patterns provide clues about direction, rate, and sequence of impacts.
- Impacted glass is compressed on the side it is hit.
- Concentric fractures form circles around the point of impact and have the same center and form on the same side of glass as a point of impact.
- Secondary fractures are concentric fractures and are on the same side as the point of impact.
- When a rock or bullet hits the glass, the side that is hit is compressed and the other side will stretch and provide tension.
- Radial fractures appear first.
- A cone-shaped piece of glass exits with a bullet, making the exit hole larger than the entrance hole.
- As a bullet passes through glass, it pushes a cone shaped piece of glass out of the glass ahead of it
- The order in which shots were fired through glass can be determined if enough glass is available.
- Radiating fracture lines from a subsequent shot will stop at the edge of the fracture lines already present in the glass.
- The exit side of the hole is larger than the entrance side of the hole
- The entrance is smaller than the exit
- If a bullet was fired perpendicular to a windowpane, the entry hole will be round.
- If perpindicular, circular, from the left blows out to the right and oval
- A high-speed bullet fired from a great distance can exhibit characteristics of a slower-speed bullet fired from a closer range.
- Bulletproof glass combines a hard and soft type of glass.
- One hard and one soft have the same refractive index, so they appear as one, transparent
- A softer layer makes the glass more elastic so it can flex instead of shattering.
- Safety glass is also known as tempered glass which is used in windshields.
- Tempered glass is heated and cooled quickly and has a hard outer surface and is found in car and building windows
- Safety glass is also known as car glass
- Safety glass is composed of two layers of glass bonded together by a layer of plastic in the middle.
- Bits of the glass can fly backwards and backscatter and creates trace evidence
- The angles at which bullets enter window glass can help locate the position of the shooter.
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