This simulation solves a truss using the method of sections, which involves “cutting” along several selected members and taking the sum of the x forces, y forces and moment about a point. Select “solve for reaction forces” to see how the reaction forces R_A and R_B are calculated. Use buttons to calculate the moment about A, do a force balance, and see the solved forces. When “calculate moment” is selected, move the mouse over the equations to see an explanation of the moment balance. Select “make cuts” to make cuts along members. See the entire truss and use buttons to select which section to make a cut along. Check “make cut” to see an isolated structure of the supports to the left of the selected cut. Force and moment balances are shown with the solved member forces. When making cuts, the sign on all of the forces is positive because we assume we can determine which members are under tension and which are under compression before solving the truss. This is done by starting at joint A, seeing that the reaction force is pointing upward, and knowing that the member force must be pointing downward for the truss to remain stationary.