This Demonstration determines whether a truss can be solved or if it is statically indeterminate by calculating the number of equations and the number of unknowns. Use buttons to make joints either rollers (one reaction force) or pinned (two reaction forces). Eliminate joint by unchecking "support at joint ". The number of members, joints and reaction forces is shown above the truss. Check "joint labels" to show labels for each joint. The point load forces are green (known forces) and the reaction forces (unknown forces) are blue.

To determine if the truss can be solved or not, a degree of freedom analysis is done:

,

where is degrees of freedom, is the number of joints, and is the number of unknowns; and , where is the number of members, and is the number of unknown reaction forces.