Does a wider dome hold less weight than a narrow one? Because full domes are difficult to build, you test this with plywood arches that share the same structural properties. You bend plywood strips of increasing length into arches that all stand 100 mm tall.
As the arch gets wider, the span (representing dome diameter) increases. You hang a pail from the center of each arch and add sand in 100-gram increments until it collapses.
The wider arches fail under less weight. This shows that increasing a dome's diameter without raising its height weakens the structure.
Hypothesis
The hypothesis is that increasing the diameter of a dome structure while maintaining its height will decrease its strength.
Proportions matter: making a dome wider without raising its height weakens the structure. To test this, you bend plywood strips of increasing length into arches that all stand 100 mm tall. As each strip gets longer, the span increases — representing a wider dome diameter. You hang a pail from the center of each arch and add sand in 100-gram increments until the arch collapses. The wider arches fail under less weight. Increasing the diameter while keeping the height fixed reduces how much the structure can hold before it breaks.
An arch's height relative to its width determines how well it spreads weight to its sides. When you bend plywood strips of increasing length into arches that all stand 100 mm tall, the wider arches produce a flatter curve. Hanging a pail from each arch's center and adding sand in 100-gram increments reveals the difference: wider arches collapse under less weight. A flatter curve weakens the sideways force distribution, confirming that increasing a dome's diameter without raising its height weakens the structure.
Bending plywood strips into arches that all stand 100 mm tall but span different widths reveals how geometry controls where a structure gets pushed together or pulled apart under load. As the span increases, the arches fail under less weight — wider diameters without added height shift more of the load into pulling forces the plywood cannot resist.
Force distribution depends on the relationship between an arch's width and its height. As the arch gets wider while staying the same height, the span increases and the structure holds less weight before it collapses. The wider arches fail under less weight, showing that increasing a dome's diameter without raising its height weakens the structure because the shape can no longer spread the load across itself as effectively.
Method & Materials
You will cut plywood into strips of different lengths, arrange bricks between two fixed pillars, and fix the plywood with the bricks at the sides. You will measure the distance between the bricks and record your measurements. You will then fix a pail at the center of the arch and gradually fill it with sand. You will record the weight of the sand in the bucket when the arch finally collapses.
You will need 4 plywood sheets, a large pail, 2 bags of sand, a weighing machine, an electric saw, a ruler, and 30 bricks.
Eureka Crate — engineering & invention kits for ages 12+ — monthly projects that build real-world skills. (Affiliate link)
The results show that increasing the diameter of the dome while maintaining its height will make the construction weaker, due to vertical stress. The hypothesis that increasing the diameter of a dome structure while maintaining its height will cause the vertical strength to be weakened has been proven to be true.
Why do this project?
This science project is interesting because it tests the strength of domes, which are used in many different types of buildings. It also shows how the shape of a structure can affect its strength.
Also Consider
Variations of this experiment include using different types of wood, such as bamboo, oak, or redwood, and increasing the width and thickness of the plywood.
Full project details
Additional information and source material for this project are available below.
