Title:

Air Drag and Friction Effects on the Bobsled

Grade Level:

6,7,8,9

Subject:

Science

Author:

nbclearn

Time:

Two 55 minute class periods

Lesson Plan Type:

Video,Interactive Instruction

Keywords:

Acceleration Aerodynamics Air Resistance/Air Drag Force Friction Gravitational Potential Energy Kinetic Energy Thermal Energy Velocity

Brief Description:

 Through discussion and the use a physics simulation program students will investigate kinetic friction and air resistance (air drag) on an object going down a hill and then design build and test different miniature “bobsled” designs.

California State Standards Addressed:

Science/9/Physics)1.0,2.0

Related Links:

Link 1:

Goal(s):

 Students will learn about the effects of air resistance (drag) and kinetic friction (sliding friction) on a bobsled. Students will develop a conceptual model to explain the relationship between initial gravitational potential energy, energy dissipated to the environment due to friction, and the gain of kinetic energy. Students will also improve their skills in communication and group work as they design, build, and test their miniature bobsled.

Specific Objectives:

Students will be able to:
1. Explain the concept of the conservation of energy.
2. Explain that the amount of gravitational potential energy decrease is approximately equal to the sum of the kinetic energy gained by the bobsled and energy transferred to the environment because of friction.
3. Describe at least one effective strategy for reducing kinetic friction for an object sliding down a ramp.
4. Describe at least one effective strategy to reduce air drag for an object sliding down a ramp.
5. Describe and explain at least two examples where reducing friction is used to succeed in another sport.

Required Materials:

• The NBC Learn Video: Banking on Speed: Bobsled
• Free Java Applet Energy Skate Park (http://phet.colorado.edu/simulations/sims.php?sim=Energy_Skate_Park)
• popsicle sticks
• toilet paper tubes
• tape/glue
• fan
• wax paper
• aluminum foil
• glossy magazine paper
• plain paper
• small weights (e.g. pennies or pebbles)

In order to build two 6 foot tracks you will need:

• 4 sections of corrugated cardboard dimension 6 inch x 3 feet (tape 2 sections together)
• optional: any suitable track material can be used as a track instead of the cardboard (e.g. poster board, rain gutter, 4 in pvc pipe cut horizontally)
• glue guns
Note: you can easily add to or modify this list depending upon available resources.

Anticipatory Set (Lead-in):

 Ask students what the following sports have in common: short track skating, bobsled, luge, and downhill ski racing. Emphasize that they are all trying to go as fast as is safely possible. Ask if there is anything preventing them from going faster and faster. Emphasize answers related to air and kinetic (sliding) friction. Tell them that they are going to spend the next two days exploring these topics as well as designing miniature bobsleds, which they are going to race.

Lesson Plan Procedure:

Part I: Reviewing Energy Principles (20 Minutes)

1. Ask a volunteer student to explain briefly what they know about bobsledding. Encourage them to pay special attention when the video discusses air drag and friction, and then show them the NBC Learn Video: Banking on Speed: Bobsled.
2. Review prior concepts of energy (this lesson assumes students have already encountered a unit on energy and are familiar with concepts of kinetic energy (K.E.), gravitational potential energy (G.P.E.), and conservation of energy.) Discuss the general energy dynamics of the bobsled competition: K.E. gained during through the process of working (force x distance) during the initial acceleration, and G.P.E. decreases over the course of the race.
3. Use the Skate Park applet to demonstrate the general energy dynamics:

I. Create a simple straight ramp with no friction and activate the Bar Graph and Pie Chart options. Stop the simulation when the skater reaches the bottom of the ramp. (Hint: It will be easier to ‘pause’ the simulation at desired place if you adjust the simulation speed to “slow”.) Observe the graph and pie chart and discuss the conservation of Total Energy.
II. Repeat several times, but gradually increase the friction. Discuss the interplay G.P.E., K.E, and Thermal Energy. Challenge students to create an equation relating the three terms.
III. Depending upon time and level of students you can explore the other graphical representations as well as effects of differing levels of gravity.
IV. Ask students to explain how this relates to the bobsled competition.



Part II: Designing the Bobsled (30 Minutes)

1. Describe the task: Students are to work in small groups to design and build the fastest possible bobsled using the materials given. Show them the testing track (at approximately 45 degrees) and set up a fan blowing up the ramp in order to amplify the effects of air resistance.
2. Describe the materials available. Each bobsled must include 2 popsicle sticks and a toilet paper roll, but they can be as creative as they want with the other materials.
3. Brainstorm briefly with the class the possible uses of the materials, including the pennies/pebbles. (Optional: you may choose to set a maximum weight as they do in real bobsled competitions, since aerodynamics become less important as mass increases. On the other hand, you might want to let the students discover this for themselves in a follow up activity).
4. Before any construction begins, each team must complete a sketch and a brief written description justifying their design decisions.

Part III: Building, Testing, and Racing the Bobsleds (50 Minutes).

1. Ideally students will have access to hot glue guns or tape in order to avoid waiting for glue to dry.
2. Give students a long piece of cardboard or access to the ramp in order to test their designs (as in actual sport competitions, some groups may want to keep their designs secret until the event.)
3. After about 25 minutes of building time, conduct the competition.
4. After the competition, lead a discussion on the experience in order to prepare them to record their reflections on the attached worksheet.
5. Have them answer the attached reflection questions either as class work or homework.
6. It’s always fun to award little prizes, and you can be creative with categories (fastest, slowest, most creative, etc.)

Closure (Reflect Anticipatory Set):

 Ask students to share anything they learned during the bobsled lesson. Ask students to identify similarities and differences between the physics involved in their mini-bobsleds and real bobsleds.

Plan for Independent Practice:

 Ask students to complete the attached reflections worksheet.

Assessment Based on Objectives:

 See the attached post-activity quiz.

Possible Connections to Other Subjects:

 Mathematics Connection: Graphing results, data tables, and averages for multiple trials.

Adaptations and Extensions:

 • The building and testing phase can be extended in order to enable students to experiment with various designs. They can be asked to perform multiple trials and record times.
• Give students time to investigate the simulation Energy Skate Park in pairs.
• Investigate effects of the angle of the ramp or different fan orientations/speeds. Would another team have won under different conditions?
• Investigate the effects of increasing the mass on the time to slide down the ramp.

Additional Notes:

 This lesson assumes students have already encountered a unit on energy and are familiar with concepts of kinetic energy, gravitational potential energy, and conservation of energy. However, these concepts can also be introduced in the context of this lesson during the introductory simulation activity “Energy Skate Park�.