| Clay Boat |
The Clay Boat activity may be the fastest introduction to designing found in DITC. It takes students 1.5-2 class periods to complete. The challenge asks students to use a given amount of clay to create a structure that can float in water while carrying the greatest number metal washers (or other load).
Clay Boat can be used as a start-up design task. Even with this straightforward task, students need to discover how to work with the building materials they are given and use tools to fashion their designs. Using a round pencil to roll the clay is one way to make it nearly uniformly flat.
There are three ways you might approach preparing students to do the Clay Boat task. Like other design activities, students can do this task without knowing any of the science related to buoyancy:
1. They can do "messing about" to investigate characteristics of the materials and different designs through testing designs and observing results.
2. They can learn about the principles of buoyancy, from which they would learn that the boat whose shape displaces more water will hold a greater load.
3. You can take a case-based reasoning approach, and give students a number of examples of things that float, from which they can draw lessons (ballast, displacement, shape) of how to design their own structure.
Archimedes described the idea behind buoyancy -- that a body will float if its displaces a volume of water that is greater in weight than the body itself. Given that each team is given the same amount of clay, the challenge of Clay Boat is to create a shape that uses the least amount of material while taking up in space the greatest volume. If the water container where they test their boats is graduates, students could collect data on different designs that show the amount the water rises (displacement) and the weights the boats held before capsizing.
What 3-D shape from mathematics maximizes volume while minimizing surface area? The sphere does this. Unlike many design tasks, it would seem that the Clay Boat task converges a single, correct answer -- students should build the biggest hemisphere that they can, and then carefully load their boat with washers until just before the water pours into the vessel.
While this is true in an ideal world -- the actual solution must take into account that the walls of a perfectly hemispherically shaped boat may collapse when loaded. Students need to give thought to how to make a boat that is both strong and spherical. Even the word "boat" can be misleading to students. Since the specifications of the challenge require that the object designed remain buoyant, and not travel through water efficiently, the preferred shape may be more like a buoy, or a bobber for fishing, than a boat with a streamlined shape.
Clay Boat can be an activity where students describe how they went about designing. You could use this context to help students creating their own names for various strategies they use when designing.
- 2 ounces of oil-based clay/team
- 200 1/4" washers/team as Load
- Basin for holding water to a depth of 2 cm
- Paper or Design Diary sheets to record designs & tests