Diameters and dome strength
The materials required for this science fair project:
- 4 plywood sheets, each measuring 1 meter x 1 meter
- 1 large pail
- 2 bags of sand
- 1 weighing machine
- 1 electric saw
- 1 ruler
- 30 bricks (add more bricks as required)
1. For this science fair project, the independent variable is the length of the arch, which will represent the diameter of the dome. The dependent variable is the amount of weight the arch can withstand before it collapses. This is determined by using the weighing machine to measure the weight. The constants (control variables) are the type of wood used, the height of the arch and the width of the sheet of plywood.
2. Cut all 4 plywood sheets into strips of 50mm width. Then, cut the lengths down to 530mm, 630mm, 730mm and 830mm and 930mm. Each length will have 4 pieces of plywood.
3. Arrange the bricks as shown in Figure 1 below, between two fixed pillars 1000mm apart or at a door entrance. Bend and fix the 530mm-long plywood with the bricks at the sides, as shown in Figure 1 below. Maintain the height of the arch at 100mm for all the plywood lengths. The sides of the door will be used to support the tension exerted by the bent plywood on the arranged bricks.
4. By either adjusting the brick arrangement or cutting the length of the plywood, keep the arch at a height of 100mm. Measure the distance D shown in Figure 1 and record your measurements in a table, as shown below. This dimension will represent the diameter of the dome.
5. Fix a pail at the center of the arch, as shown in Figure 1. Gradually fill the pail with sand, in increments of 100g. The plywood arch will gradually sink and collapse at a given weight. Record the weight of the sand in the bucket when the arch finally collapses. Repeat the test using the remaining 3 pieces of plywood of the same length, and calculate the average weight needed for the arch to collapse. Record your results in a table, as shown below.
6. Repeat steps 4 and 5 using the plywood measuring 630mm, 730mm and 830mm and 930mm in length. Record the average weights needed for the plywood arches to collapse in a table, as shown below.