Glass Flashcards
What are the two main types of fractures observed in broken glass?
The two main types of fractures are radial fractures and concentric fractures. Radial fractures extend outward from the point of impact, while concentric fractures form circular patterns around the point of impact.
Which type of fracture typically forms first when glass is broken?
- Radial fractures usually form first.
-They are caused by the initial stress wave that radiates outward from the point of impact.
How can you determine the side of impact on broken glass?
The side of impact can be determined by examining the fracture patterns:
- Radial fractures occur on the opposite side of the force application.
- Concentric fractures are more pronounced on the same side as the impact.
What is the purpose of fracture matching in forensic glass analysis?
Fracture matching, or the mechanical fit, is used to connect broken pieces of glass by fitting their edges together. This method can individualize a piece of glass to its original source.
What are the most important physical properties used to identify glass fragments?
- Density
- Refractive Index
- Additional properties include color, thickness, surface features, and fluorescence.
How is the refractive index (RI) of glass determined?
The refractive index is calculated using the Becke Line method. A piece of glass is immersed in a liquid with a known refractive index. When the refractive indices of the glass and liquid match (indicated by the disappearance of the Becke line), the RI of the glass is determined.
What factors can affect the refractive index of glass?
- Temperature: Higher temperatures lower the refractive index.
- Wavelength of light: Shorter wavelengths result in higher refractive indices.
What is the significance of density in glass analysis?
Density helps differentiate types of glass, as each type has a specific density range. It is calculated as D=M/V
How does the size of concentric fractures indicate the force of impact?
Smaller concentric fractures generally indicate a high-velocity impact, while larger fractures suggest a lower-velocity force.
Why are radial fractures used to identify the sequence of impacts in multiple fractures?
Radial fractures from a later impact will stop when they intersect radial fractures from an earlier impact, providing a timeline of events.
What are the common uses of laminated and tempered glass in forensic cases?
- Laminated glass is used in windshields and is designed to hold together upon breaking, reducing the spread of sharp shards.
- Tempered glass, used in car windows, shatters into small, blunt pieces for safety.
What is the importance of optical glass in forensic analysis?
Optical glass, used in lenses and similar items, can be analyzed for its unique properties to link fragments to specific products or devices.
