For Grade 3 students to help learn about how structures are built to withstand external forces and time.
From the Curriculum:
Students need to understand the important distinction between strength (the capacity to withstand forces that tend to break an object or change its shape) and stability (the capacity to maintain balance and stay fixed in one position), and the ways in which these two properties affect the usefulness of a structure. Students will investigate the factors that affect a structure’s strength and stability, such as its shape and centre of gravity, and apply their learning as they design and build their own strong and stable structures.
A structure has both form and function;
Structures are affected by forces acting on them. Structures need to be strong and stable to be useful.