Physical methods final exam study quide

Toolmarks - Correct Answer Anytime a harder material is pressed into softer material striations - Correct Answer sliding action, whereas indentations are a result of forcing the tool onto surface class characteristic for toolmarks - Correct Answer basic size and shape individual characteristics for toolmarks - Correct Answer caused by stria what is the first thing you do with a tool? - Correct Answer First you want to look if there is still the soft material attached to the tool - use stereomicroscope for residue types of toolmarks - Correct Answer indented - tool pushed into surface. striated - tool slides across surface. combination of both - pushed and slides on surface. collection of toolmarks - Correct Answer movable objects - should be projected and sent to lab. fixed items - take lots of pictures and then cast using silicone rubber. What should you NEVER do with toolmarks? - Correct Answer never place a suspected tool into the toolmark - could damage mark or deposit residue on the tool and/or mark what is present on the tool face or mask? - Correct Answer trace evidence What microscope should you use to compare toolmarks? - Correct Answer Comparison microscope What can the examiner conclude about a toolmark? - Correct Answer toolmark was made by that tool and no other. marks are consistent in class characteristics and show a number of similarities. marks are clearly different. inconclusive. What does a cartridge consist of? - Correct Answer case, powder, projectile, and primer case - Correct Answer container for the other 3 components powder - Correct Answer small disks, cylinders, or balls of smokeless powder (cellulose nitrate) projectile - Correct Answer (bullet) made from lead or copper coated lead primer - Correct Answer consists of a shock sensitive material "Firing Train" Process - Correct Answer firing pin strikes primer "cup" located on base of case and causes the shock sensitive primer to ignite. primer lighting powder charge. powder gives off heat. rifling - Correct Answer spiral grooves cut or impressed into barrel of a gun to cause the exiting projectile to spin and have control. raised areas - lands depressed areas - grooves class characteristics of cartridge - Correct Answer number of lands and grooves. width of lands and grooves. direction of twist. caliber. caliber - Correct Answer distance between two opposing lands in millimeters - always talk to it regarding the barrel. 3 main ways of getting class characteristics - Correct Answer Broach method, Button method, and Hammer Forging Broach method - Correct Answer long steel rod that cuts rings attached to rod. rod is pushed through barrel "cut method" Button method - Correct Answer takes plug and forces it through barrel to make it deformed. "deformation method through barrel"