Hands-on Activity: Construct It!

Contributed by: VU Bioengineering RET Program, School of Engineering, Vanderbilt University


Students use simple household materials, such as PVC piping and compact mirrors, to construct models of laser-based security systems. The protected object (a "mummified troll" or another treasure of your choosing) is placed "on display" in the center of the modeled room and protected by a laser system that utilizes a laser beam reflected off mirrors to trigger a light trip sensor with alarm.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Two photos: (left) A classroom of students working at desks with white piping. (right) Atop a table, a cube shape made with white PVC pipes and corner pieces, with a round mirror attached to one edge and a small, orange-haired troll inside.
Student teams create laser-based security system models to protect the school's treasured troll.
Copyright © 2008 Terry Carter, Vanderbilt University

Engineering Connection

While the students are building their own alarm system it is important for them to consider how mechanical and civil engineers would go about building this system in reality. Lasers are used in manufacturing warehouses where industrial products are created by mechanical engineers. They can be used for accurate and efficient cutting and welding purposes. The PVC pipe the students use could be substituted with a metal that would have been cut with a laser! Students are prompted to think like engineers in the post-activity assessment questions 5 and 6, considering the real-world means of preparing materials and safety hazards when using lasers.

Pre-Req Knowledge

Basic understanding of light properties (especially reflection) and how lasers work, as provided in this unit's lessons 2 and 3, Learning Light's Properties and Laser Types and Uses, and their associated activities. An understanding of the engineering challenge and infomercial expectations outlined in lesson 4, Security System Design.

Learning Objectives

After this activity, students should be able to:

  • Apply laser properties to construct a security system.
  • Understand and describe how the system works.
  • Understand how a beam of light can control other devices.

This activity also meets the following Tennessee Foundations of Technology educational technology content standards: 2.1, 3.2, 3.3, 3.4, 5.2, 5.3, 7.1, 7.2 and 7.3

This activity also meets the following International Society for Technology in Education (ISTE) standards: 1.1, 1.2, 2.2, 2.3, 3.1, 3.2, 6.1, 6.2; see http://www.iste.org/AM/Template.cfm?Section=NETS

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Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Apply a design process to solve problems in and beyond the laboratory-classroom. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Make two-dimensional and three-dimensional representations of the designed solution. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • precisely describe, classify, and understand relationships among types of two- and three-dimensional objects using their defining properties (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • understand relationships among the angles, side lengths, perimeters, areas, and volumes of similar objects (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • draw geometric objects with specified properties, such as side lengths or angle measures (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • recognize and apply geometric ideas and relationships in areas outside the mathematics classroom, such as art, science, and everyday life (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Materials List

Two photos: (left) A tabletop with three pieces of white pipe connectors, sticky tack, small troll with orange hair and round mirror. (right) A small rubber troll doll with wild blue hair.
Materials each group requires.
Copyright © 2008 Terry Carter, Vanderbilt University (right) 2009 Denise W. Carlson, College of Engineering, University of Colorado Boulder

Each group needs:

  • 20 feet (6 m) of half-inch PVC pipe cut into eight 18-inch (~45 cm) and four 24-inch (~60 cm) sections (PVC pipes available at hardware stores)
  • 8 three-way PVC pipe corner connectors
  • 6-8 PVC pipe "snap-T" connectors and/or 90-degree street elbows (for attaching mirrors)
  • 6-8 compact mirrors (available at discount, drug or gift stores for ~$1.20 each, example source: CTA https://www.goodybeads.com/store/products/Z003407.htm)
  • 1 laser trip sensor alarm kit
  • sticky tack (reusable adhesive), 1 package (available in stationery/school supplies section at discount, office supply and drug stores)

For the entire class to share:

  • (optional) rubber troll doll (available at toy stores) or make up your own treasure to protect

Note: A US$ 36 per group cost for non-expendable items includes PVC pipe, pipe connectors, 90-degree elbows, and compact mirrors. To reduce costs, groups may share supplies.


At the beginning of this unit, we received a challenge from our principal to create a security system to protect a valuable troll found on the school grounds. After being presented with this engineering challenge, we explored the necessary light and laser scientific properties so we have the information needed to devise a solution.

(This activity begins the Test Your Mettle phase of the legacy cycle.) Today, you will design and build a working security system, which shows whether you understand the properties of light and lasers and are able to apply these concepts to solving the challenge. Following the building stage of our challenge, you will each answer questions to be turned in for a grade.

After this activity, we will Go Public. To do this, your team will create an infomercial to convince us that you have created the most reliable and cost-effective design.


laser: A device that emits coherent light through a specific mechanism.

light sensor: A device used to detect the presence of a light source.

model: A scaled representation of an actual system.


Before the Activity

  • Gather materials and bundle them in groups for student use.
  • Arrange for level working areas for students to construct their models.

With the Students

  1. Describe the assignment to students and explain the materials provided.
  2. Divide the class into groups of three or four students each.
  3. Give enough time for students to construct a working model of a laser trip sensor system.

Two photos show two teams of students at grouped desks working with PVC pipes and components in various stages of creating cube-shaped structures.
Copyright © 2008 Terry Carter. Used with permission.

Two photos: (left) A cube shape made with PVC pipes, a round mirror attached to one edge, and a small, orange-haired troll inside. (right) A white tube with a laser pointer and metal box attached to one side.
(left) Example student-designed security system model with one mirror attached. (right) The laser with trip sensor.
Copyright © 2008 Terry Carter, Vanderbilt University

Two photos show students at cube-shaped structures made of white pipes using their hands to adjust small mirrors mounted on edging pipes, and testing to see the laser's red light reflected through a series of mirrors.
Making final adjustments to the mirrors and laser.
Copyright © 2008 Terry Carter, Vanderbilt University


Post Activity Assessment

Summary Written Test: Have each student answer the following questions and submit them for grading. In addition to the design process, these questions address the Test Your Mettle phase of the legacy cycle.

  1. Why did you select the type of laser you used in your security system design?
  2. What other technologies might make use of the laser you have used in this design?
  3. If you were to change roles and act as the thief, how could you outsmart your design?
  4. What is the purpose of the trip sensor?
  5. If you were a mechanical engineer building this system on a life-size scale using a metal frame, what type of machinery would provide the most accurate cuts?
  6. As an engineer, it is important to consider the safety of the system you have created; could anyone be harmed once your system is implemented?

Activity Extensions

If students show an interest in security systems, contact a local security system consultant to demonstrate and discuss various systems.

Have students create advertising commercials that sells potential buyers on their systems.

Activity Scaling

  • For lower grades, provide more time for construction.
  • For upper grades, provide less time for construction, using it as a real-world limitation.


Dictionary.com. Lexico Publishing Group, LLC. Accessed August 7, 2008. (Source of vocabulary definitions, with some adaptation)


Terry Carter; Meghan Murphy


© 2013 by Regents of the University of Colorado; original © 2008 Vanderbilt University

Supporting Program

VU Bioengineering RET Program, School of Engineering, Vanderbilt University


The contents of this digital library curriculum were developed under National Science Foundation RET grant nos. 0338092 and 0742871. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

Last modified: August 17, 2018