Crash Test Physics

By Jeff Gerstemeier, February 2, 2008

Grade Level

  • High School

Category

  • Product Design

Subject Area

  • Mathematics
  • Science
  • Technology

Lesson Time

Approximately three weeks

Introduction

In this lesson, students will design and test a co2-powered balsa wood dragster. They will begin with rough sketches and designs and build their cars to their own specifications which will have been informed by a careful study of Newtonian Kinematics. Students will have three to four weeks to design and build a car that will compete in time trials on a 15-meter track, while protecting a raw egg. This lesson should follow study of Newtonian Physics and the physics of motion. Vehicle crash safety concerns itself with safely surviving a rapid transition from motion to immobility. While the co2 dragster will remain a staple in physics class, this lesson gives students the opportunity to explore a more directed area of physics/automotive design/engineering.

National Standards

Science
Standard 10: Understands forces and motion Standard 12: Understands the nature of scientific inquiry Standard 13: Understands the scientific enterprise

Common Core Standards

Anchor standards for Speaking and Listening:

Comprehension and Collaboration:

CCSS.ELA-LITERACY.CCRA.SL.1 Prepare for and participate effectively in a range of conversations and collaborations with diverse partners, building on others' ideas and expressing their own clearly and persuasively.

Presentation of Knowledge and Ideas:

CCSS.ELA-LITERACY.CCRA.SL.4 Present information, findings, and supporting evidence such that listeners can follow the line of reasoning and the organization, development, and style are appropriate to task, purpose, and audience.

CCSS.ELA-LITERACY.CCRA.SL.6 Adapt speech to a variety of contexts and communicative tasks, demonstrating command of formal English when indicated or appropriate.

Anchor standards for Language:

Conventions of Standard English:

CCSS.ELA-LITERACY.CCRA.L.1 Demonstrate command of the conventions of standard English grammar and usage when writing or speaking.

Vocabulary Acquisition and Use:

CCSS.ELA-LITERACY.CCRA.L.6 Acquire and use accurately a range of general academic and domain-specific words and phrases sufficient for reading, writing, speaking, and listening at the college and career readiness level; demonstrate independence in gathering vocabulary knowledge when encountering an unknown term important to comprehension or expression.

Objectives

Students will:
  • use Newtonian Physics to make accurate predictions and to explain observed results
  • use the design process to identify, imagine, develop, execute, and evaluate solutions to a given problem
  • use various powered and hand tools to fabricate and test a model built to their own specifications and measurements

Resources

Materials

  • Car kits
  • Hand saws
  • X-acto knives
  • Sandpaper
  • Files
  • Scroll saw
  • Drill-press

Vocabulary

 
  • momentum: a property of a moving body that the body has by virtue of its mass and motion and that is equal to the product of the body’s mass and velocity
  • Impulse:  inspiration; a force so communicated as to produce motion suddenly
  • velocity: quickness of motion
  • acceleration:  change of velocity
  • displacement:  the state of being removed from the usual or proper place
  • speed:  act or state of moving quickly; rate of motion
  • aerodynamics:  a branch of science that deals with the motion of air and other gaseous fluids and with the forces acting on bodies in motion relative to such fluids
  • identify: to establish the identity of
  • imagine:  to form a mental image of something not present
  • develop:  to set forth or make clear my degrees or in detail
  • execute: to carry out fully
  • evaluate:  to assess the significance, worth, or value
  • crumple: to press, bend, or crush out of shape
  • zone: an area set off as distinct from surrounding or adjoining parts

Procedures

Set-up Set-up classroom space so that it is appropriate for the use of tools and the construction of models. Rows and columns of desks are not the best set up, instead tables (preferably work benches or lab tables) would work better. Space should be set aside for the use of various power tools such as a scroll-saw, a drill press, and rotary tools, in addition to the regular hand tools outlined in the materials section. Teacher Presentation and Motivation This project should come after a unit on Newtonian mechanics, so that students will have had a month or more of lecture and guided practice as an introduction to concepts like motion in one dimension, collisions and momentum, and energy transfer. Students should be able to do calculations regarding these concepts, and use them to make predictions and explain results. The overall project is explained below in steps. During and between each step, work with students to make sure that they are addressing the overall goal for their design, and that they are using their time wisely. Different classes will need different time allotments for each step, especially the execution stage where students will be building the models. The teacher should anticipate an average of two to three class periods for the brainstorming and drawing stages, and at least a week for the actual building of the models. Present the problem to the class: Students will design and test a co2 powered balsa wood dragster. The cars that they design will compete on a 15 meter track, while protecting a raw egg. They need to keep the parameters of their materials in mind: the balsa wood blanks are all identical 12 inch wedges which taper from about 4 inches to about 1 inch. Step 1 Break the students into groups. Students will identify the need which their car design will address. They will then brainstorm and create thumbnail sketches of at least 10 different ideas for the overall design of their car, paying attention to various ways that the car will address speed and safety. Encourage students to create a variety of ideas. Provide each group with a form divided into 10-15 spaces for thumbnail sketches. Have groups discuss the pros and cons of each design and re-design them to better solve the problem. Step 2 Tell students to select three designs from their thumbnails and develop them further. They should brainstorm together to make sure their designs are the most effective they can be. They will draw these designs on graph paper and begin to think about how to fit their ideas into the given parameters (the balsa wood blanks are all identical 12 inch wedges which taper from about 4 inches to about 1 inch). Step 3 Students will choose their best design and produce a scale drawing (blueprint) on full size graph paper that will be used as a pattern for the build stage of the project. This drawing can be cut out and taped onto the balsa wood blank, or simply traced onto the wood. Step 4 Students will use a variety of powered and non-powered tools to build their model car. They will each be provided with the body blank, axles, wheels, and an 8 gram co2 cartridge (kits from Pitsco can be used to ensure that each student starts with identical materials as a baseline). This is the segment of the project that will take the longest since students often have little wood-working experience. Make sure that time management is a big part of the students' responsibility. The deadlines are theirs, and a big part of each project is making sure they are aware of the importance of using their time wisely. Begin by teaching a few kids how to use the larger equipment and they can function as assistants and can be responsible for helping other students. By the end of the project, each student will have been able to use all of the tools at least once. The focus here is to make sure that the design blueprint is accurately transferred to the car blank, and that students take their time and produce a polished finished product. Stress the importance of proper technique with all the tools, and the importance of sanding well between paint stages. Step 5 On race day, students present their cars briefly to the class and explain how they designed various aspects to protect the egg. Close attention should be paid to timing the cars on race day. This is crucial, as times can be as close as a few hundredths of a second. Tracks and timers can be obtained from Pitsco and other companies. Step 6 Armed with distance and time measurements, as well as a broken or unbroken egg, students will write a brief report to present their test results and to evaluate their designs. These reports will include: Calculations
  • final and average velocity
  • momentum
  • impulse
  • net and frictional force
  Evaluation Students will critique their own designs and use their data and calculations to explain what worked, what didn't work, and why. They will also use their data to make inferences about how to improve their designs, and to state what changes they would make given the chance to do the project again.

Assessment

The student report at the end of the project will be used as a self-critique component of students’ overall evaluation. In addition to this self-critique, students will be graded in the following general categories. Each category can be given a possibility of achieving 20 pts, and grade appropriately. A rubric is provided with each student's grade which will include an explanation of their grade. The creativity and effectiveness of student’s design There should be a connectedness between the steps of the project in terms of the design process. In other words, the final car the students end up with should grow out of their application of the design process. Students often want to abandon the design process in the middle of the project in favor of a "cool idea" that they have halfway through. It is important to make sure that they are reflective enough that these ideas get incorporated into the design at each stage so that the project shows a conscious chain of thought. Execution Did the student pay attention to detail? Did they correctly use the appropriate tools? For example, was the cutting done precisely, did students spend enough time sanding between coats of paint. Does the model closely match the specifications on the student's blueprint? Did the egg survive?
Physics Did the student demonstrate an adequate grasp of the physics at work during the testing of the model? Did he or she correctly carry out appropriate calculations in order to make predictions during the design process and to explain results after race day?

Enrichment Extension Activities

Art students can focus on the appearance of their car in terms of shape, line, and color. Science and technology students can use wind tunnels, computer simulations, spreadsheets, CAD applications, etc., during the project. Graphic design students can create marketing materials to promote their car designs.

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