Density of Glass Fragments

Purpose:

1. To explore how the density of an object is determined.
2. To determine what a "physical property" is.
3. To demonstrate how science can be applied to police work.

Student Objectives:

1. Students will be able to determine the density of five glass fragments.
2. Students will be able to list three physical properties of glass.
3. Students will be able to conclude which known glass sample matches the crime scene glass fragment.

Materials Needed:

1. Five glass fragments from different sources - for example: mirror, Plexiglas, window, light bulb, tempered glass - all sample should be the same color
3. Scales
4. Lecture Handouts
5. Lab Handouts
6. Homework Sheets
7. Yellow Crime Scene Tape
8. Small Envelopes
9. Forceps or Tweezers

Anticipatory Set:

1. Have warm up question posted on the board as students enter the room - "How can an investigator differentiate one glass sample from another?"
2. After students complete the warm up question, tell them the crime scene story - "There was a hit and run car accident in the school parking lot this morning. The police have requested that the students from this class compare the glass fragments found at the crime scene with those taken from two suspect vehicles. You will need to report your findings to the police department as soon as possible."
3. Take students to the "crime scene" and have them collect the evidence.

Procedures:

1. Complete the anticipatory set as described above. (Day 1)
2. Pass out lecture notes and discuss in class.
3. Pass out lab handouts. (Day 2)
4. Divide class into groups of three or four.
5. Model the procedure for finding density, and then allow students to complete their lab.
6. Hand out homework assignment.

Closure:

2. Day 1 - Have students answer the following before leaving class - "List two things you learned today."
3. Day 2 - Have students answer the following before leaving class - "List two physical characteristics of glass fragments you observed during the lab."

1. Learning support and lower ability students may be provided with an outline containing fewer spaced while gifted students may be provided with a minimal outline or no outline at all.
2. The lab will be conducted in mixed ability cooperative learning groups; therefore, no adaptations are required.

Reinforcement Activity:

1. The laboratory exercise will require students to use information from the lecture.
2. Students will have a homework assignment which uses the information they gathered in the lab exercise.

Student Evaluation:

1. Students will be assessed by quizzes throughout the forensics unit to ensure that they comprehend and can apply the concepts.
2. At the end of the unit, students will be divided into groups for a "unit activity." Students will be required to collect and evaluate evidence from staged crime scenes. The evidence evaluation will require them to apply the techniques taught throughout the unit. Students will also be required to develop a report on the results of their tests and their conclusion about the perpetrator, individually after collaboration on the data.

Lesson Evaluation:

1. The lesson will be evaluated based on the homework, lab handout, and quiz scores throughout the unit. All students will be expected to receive a minimum score of 80%.
2. The lesson will also be evaluated based on the final "crime scene" project, on which students will be expected to receive a minimum score of 80%.