In this lesson, students practice investigative skills by examining and testing fibers and comparing their results to other samples. First, they examine fibers visually using magnification and record the properties they observe in a data table. In a second activity, they observe an instructor demonstration of heat tests on all 4 fibers. From these observations and tests, they determine the identity of the crime scene fiber.
Fibers are a common form of trace evidence. Easily carried from one location to another, fibers from clothing, carpet, string, and upholstery are often analyzed as crime scene evidence.
Fabrics come from four sources: animal, vegetable, mineral, and synthetic. However, there are only two types of fibers: natural and artificial. Natural fibers, such as cotton, wool, and linen, carry no human intervention. Wool, silk, and cashmere are the most common fabrics from animals. Cotton is the most common fabric from a vegetable source, and therefore seldom links a suspect to a crime. Only unique fabrics, dye colors, and fiber shapes can identify a suspect.
Seventy-five percent of all fabrics made in the US are artificial, or synthetic. This is also the most common type of fiber analyzed in criminal investigations. There are more than 1,000 different types of synthetic fibers, which are classified by fiber shape and size, chemical makeup, additives, and manufacturing method. In forensic investigations, fibers are vacuumed, taken to a lab, analyzed, and compared to known samples. This matching process can offer a link between a suspect and the scene. In this lesson, your students follow procedures similar to those in a real forensic investigation!
The activities in this lesson address Next Generation Science Standards practices of Asking Questions and Defining Problems, Planning and Carrying Out Investigations, Analyzing and Interpreting Data, and Engaging in Argument from Evidence. In addition, they address Common Core State Standards CCSS. ELA-Literacy.CCRA.SL.1 and CCSS.ELA-Literacy. CCRA.SL.2. See the Standards Matrix included in the appendix for more detailed information.