Physical Science

Exploring the Science of Automotive Air Bags

(For Teacher Notes and Student Materials, see Printer-Friendly Version of Lesson Plan)

Standard Statements

3.1.10a - Discriminate among the concepts of systems, subsystems, feedback, and control in solving technological problems.

3.1.10e - Describe patterns of change in nature, physical and man made systems.

3.2.10b - Apply the elements of scientific inquiry to solve problems.

3.2.10c - Identify and apply the technological design process to solve problems.

3.4.10a - Explain concepts about the structure and properties of matter.

3.4.10b - Analyze energy sources and transfers of heat.

3.8.10a - Analyze the relationship between societal demands and scientific and technological enterprises.

Content Objectives

Students will know that
  1. Acetic acid reacts with sodium bicarbonate to produce a gas.
  2. Acetic acid and sodium bicarbonate are the chemical names for vinegar and baking soda, respectively.
  3. The two main purposes of an air bag are to slow a person’s forward movement into the steering wheel (or dashboard) and to provide a cushion between the person and the steering wheel (or dashboard).
  4. The three parts of an air bag are the bag itself, the sensors, and the inflation system (or gas generator).
  5. The main chemical responsible for the inflation of an air bag is sodium azide, which rapidly decomposes into nitrogen gas and sodium metal when it is ignited.
  6. Other reactions occurring within an air bag ensure that highly reactive, dangerous byproducts are changed into stable and safe compounds.
  7. The inflation of an air bag and the other chemical reactions occur in a very short amount of time (1/25 of a second).
  8. The reaction between acetic acid and sodium bicarbonate is similar to the decomposition of sodium azide because both reactions produce a gas.

Process Objectives

Students will be able to
  1. Provide evidence that a chemical reaction occurs between acetic acid and sodium bicarbonate.
  2. Point out how the reaction between acetic acid and sodium bicarbonate is similar to the decomposition of sodium azide.
  3. Create a mock air bag by determining a quantity of sodium bicarbonate that will react with 25 mL of acetic acid and inflate a plastic bag.
  4. Test their mock air bag during an egg-drop crash test and determine the maximum height that their protected egg can be dropped without the egg cracking.

Assessment Strategies

  1. Evaluation of completed student handout.
  2. Group presentations of completed mock air bag designs.
  3. Evaluation of student essays from Part 8.

Suggested Level

Grades 8 - 9

Standard Category

3.1 - Unifying Themes

3.2 - Inquiry and Design

3.4 - Physical Science

3.8 - Science, Technology and Human Endeavors

Materials

Per class
  • A deflated balloon (to be blown up by you or a student)
  • Computer equipped with PowerPoint software
  • Projector and projector screen
  • PowerPoint presentation that accompanies this activity zip-seal plastic bags
  • Plastic sheet or other appropriate material to create an egg-drop crash zone


Per group of students

  • zipper-seal baggies (~3)
  • sodium bicarbonate (baking soda), ~5g
  • acetic acid (vinegar), ~100 mL
  • graduated cylinder
  • balance
  • raw eggs (can be substituted with boiled eggs for less mess)
  • facial tissue
  • paper cup
  • tape
  • meter stick


Per student

  • Copy of the history of air bag comic strip (pdf, 780kb)

Instructional Strategies

Small group

Procedures

Part 1 (1, 45-min class period)
  1. Assess what the students already know about automotive air bags by having them answer the questions that appear in their Student Handout (What does an automotive air bag do?; How does an automotive air bag work; Where are air bags found?)
  2. Have the students share what they wrote down.
  3. Show the first seven slides of the PowerPoint presentation on air bags to help the students understand what an air bag looks like and where it is located.
  4. Have the students sketch their own picture of an air bag in the box provided in their handout.
  5. Have your students watch as you (or a student) blow up a balloon. Discuss what makes the balloon inflate. Help the students understand that the balloon inflated because carbon dioxide gas was exhaled into it. Emphasize that gases cause inflatable materials (like balloons and bags) to inflate.
  6. Allow the students to think about how they would get an air bag to inflate by completing the prompt box in their handout.
Part 2 (30 min)
  1. Have the students observe the production of gas from the chemical reaction between acetic acid and sodium bicarbonate by following the directions provided in their handout.
  2. Ask the students to provide evidence that a chemical reaction occurred between these two substances.
  3. Guide the students in recognizing acetic acid and sodium bicarbonate as the common household substances, vinegar and baking soda, respectively.
Part 3 (40 min)
  1. Have the students read “Air Bags: What’s Their Purpose?” in the Additional Resources section of their handout and then have them summarize the two main purposes of air bags in the space provided in their handout.
  2. Help the students interpret what they read by showing them the slide in the PowerPoint that illustrates how force is distributed with and without an air bag (slide #8). Emphasize that an air bag helps to distribute the force of impact during a crash over a larger area.
  3. Have the students read “Timing is Everything” in the Additional Resources section, and then help them answer the questions in their handout on this reading.
  4. To make the time scale of air bag deployment more concrete for the students, have them view the 10-second online video clip entitled “Real-time deployment of air bag” from the General Motors website (refer to student handout for URL).
  5. Have students read about new design technologies for automotive air bags (“Advanced Air Bag Design” article in the Additional Resources section of the handout).
Part 4 (Hmwk Assignment)
  1. Distribute the history of air bag comic strip to each student. Have the students read it and then answer the questions in their handout about it for a homework assignment.
  2. Review the questions with the students to help make aspects of the nature of science embedded in the comic more explicit.
Part 5 (20 min)
  1. Have the students read “What’s Going On In There” in the Additional Resources section. Assist them in completing the comprehension questions associated with this reading.
  2. Help the students to realize that even though the chemicals they used in Part 2 are not the same as the ones used in automotive air bags, both chemical reactions produce a gas. (The questions in their handout are intended to help them with this concept.)
  3. Tell the students that the reason why they are using acetic acid and sodium bicarbonate in this activity is because sodium azide is highly toxic and explosive, making it too dangerous for classroom use. Acetic acid and sodium bicarbonate, on the other hand, are common household substances, safe enough to be used in a classroom.
Part 6 (20 min)
  1. Show the remaining slides of the PowerPoint to introduce students to the three main parts of an air bag. While doing so, select students to read the following parts from “The Three Parts of an Automotive Air Bag” ( Additional Resources section) aloud to the class: The bag, The sensors, and The inflation system / gas generator.
  2. Have the students construct an illustration of an air bag and its three major components using the space provided in their handout.
Part 7 (1, 45-min class period)
  1. Assign the reading entitled “Engineering Hurdles to Automotive Air Bag Development” and the corresponding questions in their handout as a homework assignment (items #19 and #20).
  2. Select students to read the four engineering hurdles in their handout aloud to the class.
  3. Tell the students that in this part of the activity, they will figure out how to create a mock air bag using the gas produced in the reaction between acetic acid and sodium bicarbonate. Emphasize the fact that they will be responsible for addressing each of the four engineering hurdles in this endeavor.

  4. Divide the students up into groups of three or four. Have the students follow the procedure in their handout for determining an appropriate amount of sodium bicarbonate to react with 25 mL of acetic acid (Engineering Hurdles #1, 2, & 3). Before allowing the students to work, point out the data table in their handout and emphasize the categories in this data table for which they will need to collect data.
  5. Prepare a crash zone (or multiple crash zone stations) by laying out sheets of plastic on the floor.
  6. Have the students follow the directions in their handout for determining how well their mock air bags perform (Engineering Hurdle #4).
  7. Allow each group of students to present how they met each engineering hurdle to the class.
Part 8 (Hmwk Assignment)
  1. As a post-assessment activity, have each student write an essay on how their group met each of the four engineering hurdles. If needed, explain to them what is meant by a “trade-off,” and instruct them to include which trade-offs they encountered while overcoming the four engineering hurdles.