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Sunrayce '93

The Turing Test

Battle of the Crazy Machines

Human-Powered Submarines

Contest Extra
in the classroom

Human-Powered Submarines

Submarines propelled by human muscles and ingenuity may not make sense tactically, but contestants racing these unique vehicles in this competition take the concept very seriously. Frontiers travels to the Florida coast, where university and corporate teams race their ingenious crafts through an underwater course. Find out which challenger has the style and stamina to win. In the final race, it's the students versus the pros.

Curriculum Links
Notes & Discussion
Activity 1: Build a Better Tower
Activity 2: Flotation Science




ocean currents


flotation science


  • Oversized eggbeaters, wide bodies, paddle wheels, wagging tails and odd-shaped propulsion devices are among the designs entered in the submarine race. Stop the tape before the winner is revealed. Can you predict the winner? What seems to be the key to a winning strategy? (Muscle power aside, simplicity of design.)

  • No matter what the end product is -- a human-powered submarine, a cathedral or an automobile, engineers must think about materials, tools and technology. How did materials factor into the design of the human-powered submarine? What might "smart" materials be able to do in the future? (Detect a problem and repair it.) What are some of the tools and new technologies used by today's engineers? (Robotics; virtual reality that allows the builder to "walk through" a structure before the ground is broken.)

  • Brainstorm examples of products designed and built by engineers in different fields. (Civil -- roads, bridges, airports. Mechanical -- automobiles, factory machines. Chemical -- paint, fertilizer, drugs, explosives. Electrical -- power plants, radio and TV, telephones. Computer -- expert systems.)

  • What qualities might characterize an engineer? (Likes to solve puzzles, interested in math, creative.) What are some structures produced by ancient "engineers"? (The pyramids, the Parthenon, the Colosseum.) Identify some contemporary engineering marvels. (The World Trade Center, the tunnel under the English Channel.)


Here's a building challenge you can try on dry land. The tower you build here won't be subject to wind or earthquakes, but you'll have to test it. Can it hold the load, or will it buckle under the weight of the brick?

  • 4-inch by 6-inch index cards (unlimited quantity allowed)
  • staples and stapler
  • 1 standard brick


Build a tower of index cards at least 11 inches high. The cards may be stapled and/or folded. The structure must be capable of sustaining the weight of a brick. It must be built as cost-efficiently as possible (see notes under Production).

  1. The tower must be at least 11 inches tall.

  2. It must be able to hold a brick on top for at least 5 seconds.

  3. The folds must be discrete (distinct).

  4. You may not use the brick to test the tower's strength before the final event.

  • Designers and engineers must also consider cost factors. Imagine that the cards represent building material costs; the staples represent assembly costs; the folds represent production costs.

  • Every card, fold and staple used costs a hypothetical $1.00. Obviously, you want to build the most cost-efficient tower using the fewest number of cards and the cleverest design. You can either keep track of the cards, folds and staples used as you go along, or add them up at the end by observing your structure (carefully). Good luck!

  • Note: Contest can be performed by teams or individuals. You may also want to add other categories, such as "most aesthetically pleasing," so everyone wins something.

  • The index-card tower challenge may not seem to have much in common with a submarine, but it follows the same engineering design-build-test process. The activity was developed by Dr. David Hoult, Senior Research Associate at MIT, and works well as a competition.


Find out what happens to a basketball when it's filled with water. What would happen to a submarine of similar density?


  • metric tape measure
  • 2 old basketballs, exactly alike
  • trough or sink into which the basketball fits
  • inflation needle
  • 2 feet of rubber tubing with a diameter lightly smaller than the wide end of the inflation needle
  • scale or heavy duty balance


Flotation science examines the behavior of objects in air and water. After you try this experiment, you'll be able to answer the question, "What do a basketball and a submarine have in common?" Try this:
  1. Insert the needle in one of the basketballs and squeeze out the air. Force the needle's wide end into one end of the tube and attach the other end to a water faucet. SLOWLY fill the ball with water. There will be air left after your first try, so disconnect the tube and squeeze it out by withdrawing the needle slightly and pressing on the ball. Put more water in the ball until it is fully inflated.

  2. Now, perform the experiment. You could do this as a demonstration for the class, if you wish. If so, place the two basketballs in front of the class. Write on the chalkboard the formulas for determining diameter from circumference and for determining the volume of a sphere.

  3. Give the tape measure and air-filled ball to another student. Have the student measure and call out the circumference. Calculate the ball's volume. Have another student weigh the ball and call out the weight to the class. Write the mass and volume of the ball on the chalkboard. Calculate the mass of 1 cubic centimeter of ball/air (surprise! this is density). Write the density of ball/air on the chalkboard.

  4. Now, lift the water-filled basketball. Ask other students to predict how high the ball will bounce. Drop the ball from chest height (be careful if it's a ratty old ball). Calculate the measurements that you did in step 3 again. Write calculations on the board. When you've finished with the basketballs, carefully place them in the trough and observe.

  1. What is the relationship between density and an object's tendency to float or sink in water?

  2. How can a submarine use the principles in this experiment to both float and sink? Explain.

  3. Submarines "hover" in water much the same as blimps do in air. What factor must be adjusted to make this happen?

  4. Use the term "density" to explain why the Titanic sank.

  5. Design an experiment that demonstrates how a submarine sinks and floats. Use simple materials like soda bottles, plastic tubing, sand or other ballast. For a real challenge, design a submarine that rises from the bottom of a water-filled aquarium and floats on the surface of the water.

  6. What principle can be applied to ships, submarines, helium-filled balloons and airships?

  7. Why does flotation science consider both air and water?

  8. How are an airship and a submarine similar, yet different?

  1. Density greater than 1 sinks, less than 1 floats.

  2. Tanks are filled with air and the boat floats; when the tanks are flooded, the boat sinks.

  3. The overall density of the boat must be adjustable to allow it to float or sink. Adjusting the density to the exact density of its surroundings allows the boat (or blimp) to hover.

  4. The ship was pierced by an iceberg, allowing water to enter. Steel has a density of greater than 1, air less than 1. The volume of air in the boat was sufficient to reduce the ship's density to less than 1. When water flooded in, its density exceeded 1, so it sank.

  5. Answers will vary.

  6. Archimedes' principle (buoyant force), which states that a body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid, applies to both floating and submerged bodies.

  7. Both air and water are fluids and both have the ability to flow.

  8. Answers will vary, but should include: both must achieve neutral buoyancy; both ascend and descend; airship is filled with helium, but submarine is filled with water; a gas (air or helium) is pumped into and out of both vehicles.

  • Use "Great Balls of Air and Water" activity for a dramatic illustration of density and related concepts of flotation science. The activity can be performed as a teacher demonstration or by students themselves. Ask the athletic department to donate old basketballs.

CREDIT: Frank Weisel, Maryland science education consultant, likes to present the Flotation Science activity as a demo for its shock value. He also contributed "The Ultimate Zeppelin" activity in this guide.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.