Activity developed by The Tech museum of innovation in San Jose, California. Click HERE for PDF of activity. Click HERE for PDF of engineering design process worksheet for bobsled activity adapted by the Museum of Science, Boston’s Engineering is Elementary.

Summary

Students in grades 3 to 12 explore the effects of gravity, friction, and air resistance upon acceleration by using the engineering design process to design, build, and test their own bobsleds with the aim of reducing run times with each attempt.

Grade level: 3-12

Time: Three 30-45 minute sessions

Learning objectives

After doing this activity, students should be able to:

• Demonstrate their knowledge of potential and kinetic energy
• Iterate on a design that decreases run times by reducing friction and drag
• Explain design considerations based on concepts of aerodynamics, acceleration, velocity, and terminal velocity
• Use the design process to meet an engineering challenge

Learning standards

Next Generation Science Standards

Engineering Design:

• Grades 3-5, ETS1-1, ETS1-2, ETS1-3;
• Grades 6-8: MS-ETS1-1, MS-ETS1-2, MS-ETS1-3, MS-ETS1-4;  Develop a model to describe that when the arrangement of objects interacting at a distance changes, different amounts of potential energy are stored in the system; Construct, use, and present arguments to support the claim that when the motion energy of an object changes, energy is transferred to or from the object. Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution.
• Grades 9-12: HS-ETS1.1- 1.3  Analyze a major global challenge, design a solution given qualitative and quantitative criteria and constratins, and evaluate and improve solutions.

Physical Science: Grade 3: 3-PS2-1; Grade 4: Physical Science 4-PS3-1 and 4-PS3-4; Grade 5: 5-PS2-1; Grades 6-8: MS-PS2-2, MS-PS3-1, MS-PS3-2, and MS-PS3-5; High School: HS-PS2-1, HS-PS2-6, HS-PS3-2, and HS-PS3-3

Common Core Language Arts

Speaking and Listening: Grade 3: SL.3.1b-d, SL.3.3, SL.3.4a; Grade 4: SL.4.1b-d, SL.4.4a; Grade 5: SL.5.1b-d, SL.5.4; Grade 6: SL.6.1b-d; Grade 7: SL.7.1b-d; Grade 8: SL.8.1b-d; Grade 9-10: SL.9-10.1b-d Grade 11-12: SL.11-12.1.b-d

Engineering Connection

Have you been in a car when the driver slammed on the brakes and the car skidded or started to chatter?  That vibration is caused by the anti-lock brake system (ABS). Engineers know that a non-skidding wheel has more traction than a skidding wheel, so they designed a braking system that prevents the brakes from locking up, which can cause a vehicle to slide. By not skidding, the static friction is maximized and the driver can stop the car quickly without loss of control.

There’s lots of engineering in bobsleds, from the aerodynamic body made of sturdy but lightweight carbon fiber materials to the

Engineers also are developing plastic bobsled tracks that not only mimic the same low-friction surface as ice when lightly lubricated with water but also heal themselves after the blade passes over. Another advantage: Plastic tracks make bobsled competitions possible year ’round, even in warm places, and reduce the environmental impact. They also cost less than today’s ice versions: around $5 million versus nearly $100 million.

The tracks, which are being studied by Jan-Anders Mansson, a professor of materials and chemical engineering at Purdue University, and software engineering Josh Dustin, are expected to premier at the 2020 Youth Olympic Games in Switzerland.

Materials

Materials can be limiting or inspirational to students! Have a wide variety of materials to promote a diversity of solutions.

“Recycled items” are really useful: 

• Old mouse pads
• Wood scraps
• Boxes
• Cardboard tubes
• Strawberry baskets

Class Supplies to Share

• Plastic Drinking Straws
• Craft Sticks
• Wooden Skewers
• Toothpicks
• Paper Clips
• Twist Ties
• Rubber Bands
• Pipe Cleaners
• Masking Tape
• Scissors
• Cardstock
• Cardboard

Testing Supplies

• Stopwatch
• Scale
• Rain Gutters (race track)
• Wood blocks (braces for the rain gutters)

Procedure

Before the activity

Make a multiple-lane bobsled course out of plastic rain gutters. Mark the start and finish lines with a dark marker, and brace the lanes with a wooden block.

Session 1: (30-45 minutes)

1. Introduce the Challenge: Design and build a bobsled using the provided materials to race down the rain gutter track.

2. Introduce the Constraints: • Each bobsled must weigh 8 grams or less. • Bobsleds must be able to fit behind the black line on the racetrack. • You must use only the materials provided. • Everyone on the team must be included (2-4 engineers).

3. Build: Give students about 20 minutes to build. Instructor should ask open-ended questions to help guide students through the design process, but should also allow students space to tinker.

4. Demonstration: Have students demonstrate their bobsled designs. If students have not completed their device, or their device did not function as expected, ask them how the device would have worked.

5. Reflection: Have each group of students explain their design strategy and how their bobsled uses energy, forces, and motion to complete the track.

The instructor should ask leading questions to get at the science behind the designs. For example: When the bobsled reaches the bottom of the track and stops, what kind of energy does it have? Potential? Kinetic?

What kind of energy does the bobsled have if it is only halfway down the track? How would a heavier bobsled affect the run? How would surface area affect your bobsled? How does shape affect your bobsled? Questions about specific design choices: Why did you use a…? What does the… do? How did you solve…?

Session 2: Directed Instruction (30-45 minutes)  

1. Questions for teaching points:

How would you describe the energy associated with your bobsled? • What would happen if you make your bobsled heavier? • What would happen if more of your bobsled were in contact with the track? • Is it possible to achieve a faster run-time just by changing the shape of your bobsled?

2. Friction: When things rub against each other, they generate friction. Materials that slide down the track more easily have less friction, less energy is lost, and so the track time is faster.

Demonstration Ideas: Have students rub their hands together. Do they feel the heat? That is the energy from the movement of their hands being converted to thermal energy (i.e. heat) through friction. Potential energy that becomes heat cannot become motion. Low friction means less energy is lost to heat, leaving more energy for motion; therefore, the bobsled goes faster. o Get a paperclip and a rubber band. Ask which one they think will go faster down the track. Drop the paperclip in one track and the rubber band in the other. The paperclip will slide down the track while the rubber band will stick at the top. Which one has higher friction? The rubber band. Things with more friction are “stickier.” Kids seem to have an innate understanding that sticky things don’t move well.

Questions: How does material choice affect the bobsled’s race time?  How does surface are affect the bobsled’s race time?

3 Aerodynamics: Air resistance, or air friction. When something moves through air, the air molecules rub against the object and create air friction. Friction slows an object down. Air friction is one form of drag. The larger the area hitting the air, the greater the number of air molecules hitting the object at any moment in time, and more friction is created. More friction means the object slows down more. This is why a parachute works.

Demonstration: Get two pieces of paper. Reduce the surface area of one piece by crumpling it up. Drop the two pieces of paper. The crumpled paper will hit the ground first. Gravity accelerates the two objects toward the earth at the same rate. The crumpled paper goes faster because there is a smaller surface for the air to hit, which means less air friction, which means it loses less speed.

Additionally: The other factor that affects air resistance is the object’s velocity. If an object can pass through more air space in a given amount of time, it will collide with more air molecules than the same object with a slower velocity. The more air molecules it hits, the more air friction is created and the more speed is lost.

Questions: How does shape affect a bobsled’s run time? What shapes are more effective? o What other vehicles make design considerations based on aerodynamics? What shapes do these vehicles utilize?

4. Terminal Velocity: Acceleration due to gravity = Deceleration due to air resistance. As an object falls it will continue to speed up. As it speeds up the force due to air resistance will increase. That force is accelerating the object in the opposite direction of its movement, or causing it to decelerate. When the force of air resistance matches the force of gravity, the object is being accelerated and decelerated at the same rate. That means there is no acceleration at all. It doesn’t mean the object stops falling. It just stops falling faster.

Demonstrations: Get a stack of cards (index or playing). Rubber band the stack together except for one card. Point out the bottom of the stack of cards and the single card have the same surface area that will hit the air when they are dropped. Hold the stack of cards and the single card at the same height and drop them. The stack of cards will hit the ground first. This is because the stack of cards has more mass so it takes longer to reach the speed that will create enough air resistance to counteract the acceleration due to gravity. If you dropped the single card and the stack in a vacuum they would fall at the same rate.

Get an empty matchbox and a matchbox full of pennies. Slide them both down the track. The matchboxes have the same profile to affect their aerodynamics. Because the box with the pennies is heavier, it will slide down the track faster.

Questions:  How does terminal velocity affect the bobsleds? NOTE: We want our bobsled to accelerate as long as possible so it reaches a high speed. Gravity will speed the bobsled up. Air resistance and friction will slow it down. Eventually, gravity will balance air resistance and friction and stop acceleration. This will be your terminal velocity. The bobsled cannot go faster than this. We want to delay reaching terminal velocity as much as possible so the bobsled accelerates as long as possible. A heavier bobsled will create a larger gravitational force (to create the same acceleration). It will take more air resistance to counteract the larger force of gravity in a heavy object. The more air resistance you need, the faster the object must be going to create it, the longer the bobsled must accelerate to reach that speed. This is why we want to add weight to our bobsleds. 

Session 3: Bobsled Redesign and Reflection (30-45 minutes)

1. Introduce the Challenge: Redesign and build a bobsled using the provided materials to race down the rain gutter track in order to decrease the initial run time.

2. Reintroduce the Constraints: • Each bobsled must weigh 8 grams or less. • Bobsleds must be able to fit behind the black line on the racetrack. • You must use only the materials provided. • Everyone on the team must be included (2-4 engineers).

3. Build: Give students about 20 minutes to build. Instructor should ask open-ended questions to help guide students through the design process, but should also allow students space to tinker.

4. Demonstration: Have students demonstrate their bobsled designs. If students have not completed their device, or their device did not function as expected, ask them how the device would have worked.

5. Reflection: Have each group of students explain their design strategy and how their bobsled uses energy, force, and motion to complete the track. The instructor should ask leading questions to get at the science behind the designs.

Questions: How did you change your original design? What affect did this/these change(s) have upon the performance of your bobsled? Did you do anything specific to increase the aerodynamics of your bobsled? Did you do anything specific to help your bobsled accelerate longer (i.e. decrease friction, delay terminal velocity by adding weight and increasing aerodynamics)? If you had more time what would you add, change, or do differently? o If you had another opportunity to redesign, do you feel you could make your bobsled run even faster?

Nigeria is sending its first bobsled team to the Pyeongchang Olympics. Jamaica’s 1988 bobsled team, subject of the movie Cool Runnings, says its debut at the Calgary Olympics was an even crazier experience than depicted in the film.

Resources

How Bobsledding Works An article by “How Stuff Works” on bobsledding provides information on the rules of the sport, technical information about courses and sleds, and the physics of how everything works.

Aerodynamics An article posted to “Live Science” that explains the basics of aerodynamics as it applies to a variety of vehicles.

Engineering Faster and Safer Bobsleds A National Science Foundation video explaining the engineering challenges associated with making sleds faster and tracks safer. The video is narrated by Michael Scully, of BMW DesignWorks USA, and mechanical engineer Mont Hubbard, professor emeritus at the University of California, Davis.

PhET Interactive Simulations. Interactive simulations for science and math from the University of Colorado, Boulder, includes an interactive skatepark (or snowboard half-pipe) graphing simulation that lets students manipulate a ramp in order to discover force, energy, and work.

Science of the Winter Olympics: Banking on Speed. National Science Foundation and NBCLearn video explains how the U.S. Men’s Bobsled Team hopes to win gold for the first time in decades at the Vancouver Olympics with the help of scientists, phyiologists, physicist George Tuthill of Plymouth State University, and bobsled designer Bob Cuneo.

Video of going down bobsled track. From Pyeongchang 2018 Olympic Bobsleigh official site.

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Filed under: Class Activities, Grades 6-8, Grades 9-12, Grades K-5

Tags: 2018 winter Olympics, Aerodynamics, Bobsled, Class Activities, Engineering Design Process, forces and motion, friction, Grades 6-8, Grades 9-12, Grades K-5