OBJECTIVE: Students will conduct a scientific experiment to determine the weight required to support different lengths of cantilevers.
- 100 planks per group
- 1 KEVA "Yardstick" per group
- 1 Data Sheet per group
- 1 Classroom Data Chart per group
Introduce the class to the principle of cantilevers: a cantilever is a projecting beam supported at one end by a counterweight. Demonstrate a cantilever by laying a ruler or yardstick so that it extends over the edge of a table.
Before conducting this exercise, discuss with the class the importance of controls in experimental procedures. The edge of the table should be the starting point for each measurement; KEVA planks should be stacked along the end of the yardstick, even with the edge.
Divide the class into small groups and ask them to use KEVA to measure how many planks are necessary at one end of a yardstick to support a stack of 2 KEVA planks at the other end of the yardstick when it is hanging over the edge of a table by 6 inches; 12 inches; 18 inches; 24 inches. [The stack of 2 planks can be taped to the end of the yardstick using a 6” length of tape (control) to cut down on clatter in the classroom.]
Have each group complete a data sheet, then graph their results.
You can compile the data from the groups. Explain to the students that this can be done because of the controls used in the experiment. Have the students take an average of the classroom data.
Discuss the results with the students. What conclusions can they draw? [The longer the length of yardstick hanging over the table, the more weight is required to stabilize the cantilever.]
SCIENCE EXTENSION: You can modify this experiment by fixing the length of yardstick hanging over the edge of the table and varying the number of planks added to each end of the yardstick. What conclusions can the students draw from the results of this modification?
BUILDING EXTENSION: Have students build structures with cantilever designs.
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