Degrees of Freedom Explained: Why Walls Don't Move
A door can move. A wall cannot. The difference is degrees of freedom : the number of independent ways a structure can move. This video explains the idea in about 7 minutes, with animations, and shows why every structural engineer needs it. What you will learn What a degree of freedom is. A block on a table has 3 (two slides and one spin). A body free in 3D has 6. Joints and members. Each joint of a 2D truss has 2 degrees of freedom, a 2D frame joint has 3, and a 3D frame joint has 6. The structure and its connections decide the count. Supports remove freedom. A roller removes 1, a pin removes 2, and a fixed support removes 3. Every restraint adds a reaction. Counting for stability. For a planar truss, compare the unknowns (members + reactions) with the equations (2 per joint). Fewer unknowns than equations means a mechanism, equal means statically determinate, more means indeterminate. A passing count is not enough: the arrangement of members and supports must also be stab...