1. Glass

2. Frontline: The Real CSI

3. Many solids are crystals
A solid in which the atoms are arranged in a regular pattern
Sodium chloride

4. Glass is an amorphous solid.
A solid in which the atoms are in no order.
It is also brittle
Shows a conchoidal (circular) fracture pattern,
Hardness, and elasticity of shape.
Primarily composed of silica (SiO2) and various amounts of elemental oxides

5. Types of Glass a. Soda-lime glass
Most common commercial glass (90% of total production)
Used in plate and window glass, electric light bulbs
least expensive

6. Composed of: Sand (silica…SiO2) Soda (Na2O) (reduces melting pt)
Lime (CaO) (water insoluble)

7. Soda-lime glass is used for:

8. b. Borosilicate glass strong heat resistant (ex. Pyrex)
contains boron oxides (B2O3)

9. c. Tempered Glass. 1. made stronger than soda-lime glass
c. Tempered Glass 1. made stronger than soda-lime glass by rapid heating and cooling 2. used for side and rear windows in cars

10. Also used in…

11. Tempered glass breaks into….

12. d. Laminated glass
For windshields

13. Glass Experiements

14. e. Soda-lead glass commonly called crystal or lead glass, expensive
widely used for the finest tableware and art objects, radiation protection
Lead- increases density and refractive index (sparkle)

15. Comparison
Individualized evidence (jigsaw fit)

16. Physical Characteristics making up class evidence
Density
Refractive index (RI)—the measure of light bending due to a change in velocity when traveling from one medium to another
Fractures
Color
Thickness
Fluorescence
Markings—striations, dimples, etc

17. Density
Mass per unit of volume
Density = Mass/Volume

18. Class characteristics
1. Flotation
Used to find the density of glass by floating glass particles in liquids of known densities.

19. Refraction

20. Refractive index (RI) Formula RI = velocity of light in vacuum
velocity of light in medium
The RI of water at room
temperature is 1.333

21. Refractive Index
Test tube demo- water vs veg. oil

22. 2. Immersion method – used to find the Refractive Index of glass

23. When the Becke line disappears
MATCH POINT The point at which the Becke line disappears
The RI of the glass = RI of the oil
When the Becke line disappears

24. The Becke Line
The Becke line is a “halo” that can be seen on the inside of the glass on the left, indicating that the glass has a higher refractive index than the liquid medium. The Becke line as seen on the right is outside of the glass, indicating just the opposite.

25. Data bank Densities Refractive indices Relative frequencies
in the glass
pop of US

26. Fragments Radial fractures- radiate out from the origin of the impact
they begin on the opposite side of the force

27. 2. Concentric fractures. a. lines are circular lines around the
2. Concentric fractures a. lines are circular lines around the point of impact b. they begin on the same side as the force

28. Name A and B B A

29. b. First Fractures Form on the side of the glass OPPOSITE
the side of the penetrating object

30. c. Next Fracture
Forms on the SAME side of the glass as the penetrating force
Forms concentric fractures
Puts tension on front surface causing concentric fractures
A high-velocity projectile leaves a wider hole on the exit side of the glass (helps determine direction of impact)

31. How does Glass break?

32. d. Stress markings

33. A determination of the direction of force in breaking a window pane:
-direction of the rib marks
[stress marks on broken edges of glass that are perpendicular to one side of glass]
3R rule—radial cracks form a right angle on the reverse side of the force.

34. Fracture Termination
Which bullet hole was made first?

35. Also know…
Blowback
- the backscattering of particles toward the direction of the force.