A Good Source of Fiber: Fiber Analysis

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SWBAT perform physical and chemical analysis of fibers in order to form scientific conclusions.

Big Idea

Even the smallest fiber left behind at a crime scene can provide BIG clues!

Day 1: Engage

15 minutes

I start each class period in this unit with a warm-up activity that targets forensic science concepts and other skills (listening, observation, problem-solving, etc.) Not only does this get the students in the frame of mind necessary to address the field of forensics, but it also introduces key vocabulary they will use throughout the unit in a more relevant way. In addition, this activity allows students to refine their research skills as they perform quick internet searches to find the correct answers. By using the attached weekly Answer Sheet* and passing it out as they enter the classroom every Monday morning, not only can I save paper, but I can also provide a routine that allows students to begin without prompting, waiting for paper, or asking things such as, "What do we do?" and, "Where do we write our answers?"

For this particular lesson, I have decided to utilize a Video Challenge* in which students watch a short video clip about forensics and follow up by answering an assortment of trivia questions.

After providing about 2-3 minutes to choose the correct answers, we go over them together and discuss the information provided. I help students to define key terms and providing background knowledge necessary to help students understand the questions. However, I do not spend as extended period of time on this portion, as it is just meant to be an activator and not necessary to understanding the core of the lesson at this time.

I pass out copies of the Hair and Fiber passage, provided by the Science Olympiad. We read the first three pages (about fibers) ONLY together as a class. After each paragraph, I have the students draw in the margin what they think each type of fiber looks like under a microscope. For each fiber type, I ask a random student to explain what makes this fiber unique and have 1-2 students compare their drawings under the document camera.

*Challenges and answer sheet courtesy of http://sciencespot.net/Pages/classforscistarters.html

Day 1: Explore

40 minutes

Next, I pass out pages 3 and 5 of the Fiber and Forensics Lab, created by the Illinois Museum of Science and Industry, as well as 3in. x 3in. samples of each of the following fabrics*, to each table group:

  • Wool (labeled "sample A")
  • Cotton (labeled "sample B")
  • Silk (labeled "sample C")
  • Polyester (labeled "sample D")
  • Rayon (labeled "sample E")

*DO NOT tell students what type of fabrics you have passed out! They will work to figure this out.

I also have a designated Materials Manager collect the following materials

  • microscope
  • slides
  • slide covers
  • scissors
  • dropper or pipette
  • water

I explain to the students that they will look at several samples of fibers under a microscope and draw their observations. After drawing what they see under three different magnifications (low, medium, high), I have them use the passage they previously read and access the Fiber Reference Image Library to determine what type of fibers they were given.

Day 2: Explore

40 minutes

I pass out the Wonderville Fiber Analysis Lab**, page 6 of the Fiber and Forensics Lab, and have the designated Materials Manager collect their fabric samples from the day before, as well as the following materials:

  • forceps
  • paper towels
  • tea-light candle
  • small cup of vinegar
  • small cup of acetone nail polish remover
  • 2 non-plastic dishes
  • marker
  • safety glasses (1 per student)

As a class, we go over the procedures involved in both labs. I ask students to summarize, in their table groups, what they are expected to complete before the lab period is up. I listen to the discussions, listening to ensure that each group understands that they are to perform three different tests (flame, vinegar, nail polish) to see how different fabrics respond to them.I designate a Lab Director for each group to write down their summary and to make sure all group members stay on task throughout the duration of the lab.

I explain to the students that as they conduct this lab, they must work as a group to create a chart or table to organize their data and observations in a way that is understandable to themselves and others. I designate one Scribe for each group to fill in their data once the group agrees on a chart or table structure.

**Even though this lab calls for samples of wool, cotton, and silk, we perform the tests on all 5 types of fabric in order to equally compare to the results our microscope lab.


10 minutes

After completing the labs, I have each table group partner up with the group nearest to them. They share their charts/tables, in order to communicate their data and compare their results. If a group got very different results for the same type of fabric, I have them repeat that part of the lab, in order to see which results are most accurate and to determine where/how they made their mistake. Students will revise their data tables as necessary to include the most accurate information.

Day 3: Elaborate

30 minutes

Next, we will apply our knowledge of fiber analysis to its implications on forensic science. We will do so by watching an episode of the series, Forensic Files, entitled, Material Evidence.*

After watching the episode, we discuss the importance and implications of forensics on the case in an engaging way that promotes student-to-student interaction, engagement and a little fun. I pose the following question to the class:

"Why was forensic science crucial to solving this crime?"

Next, I take out a Koosh ball and toss it gently to a student. The student who catches the Koosh ball must answer the question, then pass it to a peer.  Their peer will restate the first student's answer, then add their own response. For example, I pose the question to the class, then pass it to Josh. Josh says, "Because of forensics, the investigators were able to find DNA evidence and match it to the victim." Then, he passes to Katie. Katie responds with, "Forensics made it possible to match the DNA to the victim AND it also allowed scientists to match the fibers found on the victim to the fabric in the suspect's car."

We keep passing the Koosh ball around until there are no more responses left to discuss. The students are allowed to pass to anyone they want, even if that student has already answered. However, they cannot throw to anyone who has thrown it to them or who they have already thrown to. This ensures that any student could be called on at almost anytime, making engagement mandatory, but keeps the same few students from always getting a chance to speak. I follow this same procedure for the following questions:

  • What evidence was collected at the crime scene?
  • What kind of tests were conducted by forensic scientists?
  • How did fiber analysis become important to solving the crime?
  • What could investigators have determined about the crime without the use of forensic science?


 *This video shows footage and discusses details of actual crimes. it may be necessary to get administrator and/or parent approval prior to showing. This portion of the lesson can be omitted if necessary.


25 minutes

Finally, students will apply their knowledge of fiber analysis to help identify an unknown fabric. I pass out small baggies of mystery fiber samples to each group. (This can by any sort of fabric you choose. it can be the same for every group, or different.) Students will perform the same tests on the unknown sample (microscope, flame, vinegar, acetone) and collect data using the Mystery Fiber ID Sheet. After performing the tests, students must identify their fiber and write a summary of their findings, including evidence and data from their tests to back their claim as to which fibers they believe they have identified.

As a final way (or alternative) to evaluate whether or not students have met the objectives for the lesson and understood the content , I have them work independently to answer the "Did They Get It? Post Lab Questions" on the Fibers and Forensics Lab. I have rewritten the questions in a format that makes it easier for them to provide a corresponding response to each question.