Cantilevers (based on Fallingwater)
In this lesson, students will learn what a cantilever is, and design and build one that can withstand at least 2 pounds of weight.
Grades: 6 – 12
Time: 2 periods
This lesson addresses selected themes from McRel Science Standards
- Standard 10: Understands forces and motion.
Level III (grades 6 -8). Understands general concepts related to gravitational force.
Level IV (grades 9 – 12). Knows that laws of motion can be used to determine the effects of forces on the motion of objects.
- Standard 12: Understands the scientific inquiry.
Level III (grades 6 – 8). Designs and conducts a scientific inquiry.
Level IV (grades 9 – 12). Designs and conducts a scientific investigation.
To prepare to teach this lesson, teachers should:
- Popsicle sticks (maximum of 200/group) Note: The large “tongue depressor” size might be easier to use
- Hot glue guns with glue sticks Note: Use “low-temperature” hot glue guns only.
- Piece of foam board or corrugated cardboard for model bases, approximately 8” X 8”
- Blank paper for sketching
- Copies of Sample Cantilever Construction Instructions
- Strong tape like masking tape or duct tape
- 2 pound weights
- Heavy books
- Ask students to share their reaction to Fallingwater. Encourage them to use describing words to talk about the structure. Ask them if they remember what a cantilever is. Ask students to define a cantilever.
- Ask for two volunteers to come up to the front of the room. Explain that they will act out different types of construction: one, a cantilever, and the other, traditional post-and-beam construction.
- Take a pile of books or weights that weigh about the same amount. Pile one group on top of one student’s head. Have the other student extend his or her arm and pile the books in his or her hand. Who can stay in position for the longest time? (The student with the books on his or her head will last the longest.)
- Explain that the student with their arm extended is a cantilever. The other student represents post-and-beam construction. Why is the post-and-beam student able to hold up the books longer? Elicit the answer that all of the weight that the student is holding on his or her head is supported underneath. The cantilever (the arm) on the other hand, has no support underneath, and that’s why the student’s arm begins to droop and sag.
- Explain that this is the genius of Fallingwater—how Wright designed and built the cantilevers to be so long but also so strong. Ask if anything could be done to the student (whose arm is drooping) to make his or her “cantilever” withstand the additional weight? Have students share their ideas. One idea might be to place a column or support under the student’s arm. That would certainly help support the arm, but then it wouldn’t be a cantilever any more. Tell students that Fallingwater was unique in the way it utilized cantilever construction. Wright also was very smart in manipulating the materials and “folding” the concrete to make the cantilever stronger.
- Tell students that they are going to design and build a cantilever that must withstand at least 2 pounds of weight.
- Divide the class into groups of 4. Each group will design and build a cantilever. Tell students that they must build the support tower and the cantilever that extends from it. The cantilever must extend from the support tower at least 10 inches.
- Design brainstorming and safety. Please take some time to go over hot-glue safety with your class before letting them build. They must NEVER touch the tip or the glue when it is in its molten state. They may ONLY touch the trigger and handle of the glue gun. They must be aware of cords and be careful not to trip.
- Distribute copies of “Sample Cantilever Construction Instructions.” Ask students to share their observations. They may observe that there are lots of “x’s” in the design. Why is that? (Elicit that triangle and x’s make cross-bracing and create a stronger design than just plain squares.) Encourage students to use as many triangles as possible in their designs. Tell them that they may use the sample as a guide, but should try to come up with their own design.
- Distribute sketch paper (blank paper) and have students work up a design.
- Distribute building materials and students may begin building.
- Students continue building.
- Students test the weight of their cantilevers. When they test the weight, they must place the weight at the far end of the cantilever. NOTE: Before they test the weight, they will have to tape down or weight down the cardboard base to act as a counterweight. Otherwise, the entire structure will simply tip over.
- What happened? Why? Did the cantilever hold? For how long? If it started breaking, where did it break? Students assess the integrity and strength of their designs and what might have been done to make them stronger.
- The Engineering Book: From the Catapult to the Curiosity Rover by Brian Marshall
- Why Buildings Stand Up by Mario Salvadori
- The Art of Construction by Mario Salvadori
- The Story of America’s Bridges by Ray Spangenburg and Diane K. Moser.
- Fallingwater Rising: Frank Lloyd Wright, E.J. Kaufmann, and America’s Most Extraordinary House by Franklin
- dezeen magazine feature about worldwide architecture with cantilevers
For Further Study
This Art lesson can be extended to other subjects or paired with other 10 Homes that Changed America lessons to create the following interdisciplinary connections:
- Art: Trees—nature’s cantilever. Have students study the “architecture” of trees by studying and drawing (on site) tree trunks and branches, and how branches cantilever out from the trunk.
- English Language Arts: Students write a “How-To” book that describes the process of designing and building the cantilever out of popsicle sticks.
- Mathematics: Analyze which shapes were the strongest in the students’ designs of cantilevers. Squares? Rectangles? Triangles? Students may analyze which shape is the strongest and why.
- Social Studies: Frank Lloyd Wright used concrete in novel ways in the construction of Fallingwater. Students may conduct research about the earliest use of concrete in Ancient Rome and then create a travel catalogue that depicts examples of concrete architecture around the world.