Free Body Diagram Builder
A Free Body Diagram is the first step in solving any statics or dynamics problem. Isolate the body, replace every contact with a force, and check equilibrium.
This interactive builder lets you do exactly that on a beam. Tap to place point loads, distributed moments, and three support types (pin, roller, fixed) anywhere along the span. Each support automatically shows the reactions it provides: pin gives Rx and Ry, roller gives Ry only, fixed gives Rx, Ry, and moment M.
Hit Solve and watch the reaction forces appear as green dashed arrows. The equilibrium check (∑Fx, ∑Fy, ∑M) updates live after every placement, turning green when all three are zero.
The builder handles simply supported, cantilever, and overhanging configurations.
Built for first-year engineering statics, GATE preparation, and anyone learning to draw FBDs correctly before touching a single equation.
A horizontal beam with a toolbar above it. Tap a tool, tap the beam, and the force/support/moment appears instantly. The equilibrium check (∑Fx, ∑Fy, ∑M) updates live after every placement.
Try this simulation yourself
Start with the Force tool selected (red dot, active by default). Tap the beam near the center. A 100 N downward force appears. The ∑Fy card immediately shows -100 N in red. The beam is not in equilibrium because there are no supports yet.
Select the Pin tool from the toolbar. Tap the left end of the beam. A triangular pin support appears with ground hatching. The label says "Pin (Rx, Ry)." The equilibrium check still fails because one pin alone cannot balance the moment.
Select the Roller tool. Tap the right end of the beam. A triangle on small wheels appears, labeled "Roller (Ry)." Now hit Solve reactions. Two green dashed arrows appear: RAy at the left and RBy at the right. If your force is at the center, both reactions are 50 N. All three equilibrium cards (∑Fx, ∑Fy, ∑M) turn green. The pill at the top reads "∑F = 0 ✓."
Select Move from the toolbar. Drag the force from the center toward the left pin. Watch the reactions change live. As the force gets closer to the left pin, RAy increases and RBy decreases. At the pin itself, RAy carries the entire load and RBy drops to zero. The moment balance shifts continuously.
Add a second force. Select Force again and tap at a different position on the beam. Now the beam carries two loads. Hit Solve. Both reactions adjust to balance the new total. The position labels below the beam show each item's location as a fraction of L (0.00L to 1.00L), matching how textbook problems specify load positions.
Select the Moment tool (purple) and tap the beam at midspan. A curved arrow appears showing a 50 Nm couple. Notice that ∑Fy does not change (moments have no vertical force component) but ∑M jumps by 50. Hit Solve again. The reactions adjust to balance the added moment without changing the total vertical force. This is the key difference between forces and couples.
Try a cantilever. Hit Clear all to start fresh. Place a Fixed support at the left end (wall with hatch marks, labeled "Fixed (Rx, Ry, M)"). Place a single force at the right end. Hit Solve. Three reactions appear at the wall: RAy (vertical), RAx (horizontal, zero for a vertical load), and a moment MA. The fixed support carries everything alone. No second support needed.