Forensics Study Guide (Glass & Ballistics)

What does the General Rifling Characteristics File have?

Class characteristics, lands and grooves dimensions, and directions of twists

Define Visible Light

Colored light ranging from red to violet in the electromagnetic spectrum.

Define Concentric Fracture

Cracks that encircle the bullet hole or point of force.

Define Radial Fracture

Cracks that radiate outwards.

What shapes does the glass break into? How big? Edges?

Cubes and circles, eraser sized, and has smooth edges

What do the forensic experts do once they find a bullet at the crime scene?

Find Bullet, Find the suspects gun, Bring it to the crime lab, Fire into the gel tank, Use a comparison microscope.

What type of glass is used for windows?

Float glass

Define Rifling

The spiral grooves formed in the bore of a firearm barrel that impart spin to the projectile when it is fired.

What evidence do they look for?

The type of gun, caliber of the bullet, # of shots fired, location of shooters if weapon has been fired recently, and if the gun is connected to any other cases.

What does IBIS do?

They use digital microscope images found on expended bullets and cartridges

If the target is within _____ft the target will have powder

Three

Griess test for GSR

1) Use swab of cotton w/ 5% nitric acid. 2) Front and back of each hand swabbed separately 3) Obtain a 5th control area w/out GSR

If the shooter is 30 yards away how much of the target will get punctured by shotgun pellets?

28 inches

How many layers does laminated glass have? What are they?

3 (Like a sandwich), Glass-Thin Sheet of Plastic-Glass

How many pellets does a 28 gauge shotgun have?

300

How far does GSR travel?

36 inches

Define Becke Line

A bright halo observed near the border of a particle immersed in a liquid of a different refractive index.

Define Sublimation

A change of state from a solid directly to a gas. (Like dried ice being placed into water)

Define Griess Test

A chemical test used to develop patterns of gunpowder residues around bullet holes.

What shape does the bullet make?

A cone

Define Birefringence

A difference in the two indices of refraction exhibited by most crystalline solids.

What is glass?

A hard brittle substance, typically transparent.

Define Crystalline Solid

A regular atomic structure. (Nice and organized, like my bedroom because I like things to be crystal clean.)

What is the gun barrel made of?

A solid bar of steel that has been hallowed out by drilling

Define Laminated Glass

A thin layer of flexible clear plastic film between two or more pieces of glass.

Define Cartridge

A type of ammunition packaging a bullet or shot, a propellant substance, and a primer within a metallic, paper, or plastic case that is precisely made to fit within the firing chamber of a firearm. (Also called a round or a shell)

Glass info:

Adding metal oxides with glass mixtures gives different colors, densities, and refractive indexes.

Air and Glass... Which is less and more dense?

Air is less dense and glass is more dense

Define Amorphous Solid

An irregular atomic structure, glass brakes into a variety of fracture patterns. (Messy like Kaitlyn's room because she isn't as A-More-Fussy as me. Just go with this example that does't make sense. Thanks.)

Define Refraction

Beams of light & other waves that travel at different speeds through different types of substances or mediums.

Where is tempered glass most commonly used?

Car windshields

Internal Characteristics

Each gun has individual markings

What do Forensic experts compare when looking at glass fragments?

Density and Refractive Index

What are the class characteristics of a rifled barrel?

Direction of twists, lands, grooves, and the width.

Refractive index of a medium is _______ to the ratio of the speed of light.

EQUAL

What happens when the bullet leaves the barrel?

GSR

Define Tempered Glass

Glass that has had strength added to it by introducing stress through rapid heating and cooling.

What are the 2 major forces in the bullet once fired?

Gravity --> The downward force Trajectory --> The forward force

What are three factors that can prevent an examiner from obtaining a perfect match of striation marks?

Grit/Rust, Mutilation/Distortion, and Striations not being permanent

What is GSR?

Gun shot residue which are particles of unburned powder and traces of smoke

What does IBIS stand for? What is it the bureau of?

Integrated Ballistic Identification System. Alcohol, tobacco, and firearms unit.

What is different about shotguns compared to every other gun?

It has a smooth barrel without any markings

What is window glass? What happens when it is hit?

It is a glass that does not make clean breaks and instead, shatters into a bunch of fragments, both large and small. When hit, a circle forms around the point of impact.

What is the purpose of the plastic in laminated glass?

It keeps all of the glass fragments together, lessening injuries. The film can stretch but the glass still sticks.

Define Primer

It reacts chemically to produce heat which ignites the main propellant charge and fires the projectile.

What happens when a wave moves through one medium to another?

Its velocity changes causing the wave to bend... REFRACTION INDEX

More dense ---> less dense

LARGER ANGLE OF REFRACTION

FINAL QUESTION: WHO IS STILL GOING TO FAIL THIS TEST???

NOT ME!!!!!!!!!!! MAYBE VANESSA BUT NOT MEEEEEEEE!!! MUAHAHAHAHAHAHA

What is the only way to individualize glass fragments to a single source?

PUT THEM ALL BACK TOGETHER

UPON IGNITION OF THE CARTRIDGES POWDER CHARGE, A _____ OR _____ WAD PUSHES THE PELLETS THROUGH THE BARREL

Paper or Plastic

A round entry means the bullet was from a _____ angle? If it is fired from an angle the glass will go _______?

Perpendicular, Outwards Bits of glass will fly backwards (TRACE EVIDENCE)

What is not a physical state of matter?

Plasma

What is ballistics the study of?

Projectiles, Trajectories, and the Effect on the target

What is the 3R rule?

RADIAL cracks form a... RIGHT angle on the ... REVERSE side of the force.

You told the police that if you could examine the actual broken glass, it would be possible to determine the direction in which the bullets were fired, from the inside or the outside. What are two methods you could use to determine the direction of the bullets?

Radial and concentric fractures.

Common applications of tempered glass?

Rear and side windows on cars, Glass shower doors, Coffee carafes, Oven door windows.

Less dense ---> more dense

SMALL ANGLE OF REFRACTION

What formulas can you use to find out where a bullet was shot from? (PRACTICE PROBLEMS ARE ON EDLINE)

SOH CAH TOA a^2 + b^2 = c^2

What is tempered glass also known as? Why?

Safety glass because it breaks into small pieces that will only cause superficial wounds.

Concentric fractures form on the ______ side as the impact.

Same

Impacted glass compresses on the ________ side it is hit. The tension will radiate _______.

Same side Outwards (Radial Fractures)

What is glass made out of?

Sand, soda (baking soda), and lime

When does tempered glass break?

Shatters along stress lines and when it falls

What is a Amorphous Solid made of?

Silica, calcium oxide, and sodium oxide.

If the destiny of a solid is greater than the liquid it will ____.

Sink

Define Gauge

Size designation of a shot gun, originally the number of lead balls with the same diameter as the barrel that would make a pound. (Basically the caliber of a shot gun)

The higher the gauge, the ___ the diameter

Smaller

What glass is used in bottles and windows?

Soda lime glass

Where should glass evidence be stored?

Solid containers

What are characteristics of tempered glass?

Strong and heat resistant

Define Bullet

TADA! You watch Criminal Minds, NCIS, and CSI. You know what a bullet is.

What are the 2 types of safety glass?

Tempered and Laminated

What does the Greiss test check for?

Tests for barium and antimony rather than nitrates

What are the records that the FBI has in regards to guns?

The General Rifling Characteristics File

Define Grooves

The cut or low lying portions between the lands in a rifled bore. (Think of the stuff that is growing as the lands and the dirt as the grooves. The dirt is lower than the plants.)

Define Caliber

The diameter of a rifled guns barrel. Expressed in hundredths of an inch or millimeters.

Define Wave Length

The distance between crests of adjacent waves.

What is larger? The entry or exit wound of a bullet?

The exit

Define Bore

The interior of a firearm barrel.

If you have a sheet of glass and the fragments are shattering to the right, what side of the glass was shot at?

The left. It will always be the opposite because the glass goes away from the applied force.

Define Ejector

The mechanism that throws the cartridge or fired case from the fire arm.

Define Breechface

The near part of a firearm barrel. (Show them your 'breech face' hahahahahahahaha.)

Define Lands

The raised portion between the grooves in a rifled bore. (Think of the stuff that is growing as the lands and the dirt as the grooves. The plants are above the dirt.)

Define Refractive Index

The ratio of the speed of light in a vacuum to its speed in a given medium.

How many reference points are needed to determine the position of the shooter?

Two

Define Magazine

Where all the bullets are stored.

LOOK AT OTHER SIDE OF FLASH CARD FIRST ============================================= (The fracture closest to the speaker was second and the fracture closest to the home button was first)

Which fracture would have come first if this was a window with bullet holes? (*cue James Bond music and James Bond voice*, "The investigation of the cracked phone screen.")

Common applications of laminated glass?

Windshields, Skylight windows, Widths tans hurricane strength winds

Do they have to put all the glass pieces together again?

Yes. No Thanks. That is way to much work.

How do you calculate density?

density = mass/volume