A free body diagram maker for statics and dynamics coursework. Draw force arrows, moment arcs, lines, rectangles, ellipses, dots and 3D cylinders, label them, then copy a PNG to paste into Word or Google Docs, or download PNG, SVG or PDF.
Ctrl+Z and Ctrl+Y undo and redo. Scroll to zoom, or pinch with two fingers on a touch screen. Click and drag the background to pan.
A free body diagram (FBD) is a sketch that shows all the forces and moments acting on a single object, isolated from its surroundings. The object is drawn as a simple shape; everything else is replaced by the forces those surroundings exert on it. This isolation converts a physical situation into a model you can apply Newton's laws to.
For a static object, the sum of forces in each direction equals zero and the sum of moments about any point also equals zero. These equilibrium equations let you solve for unknown reactions, cable tensions, or applied loads.
A complete FBD includes: the isolated body, all applied external forces with directions and labels, reaction forces at supports, and the weight of the object at its center of gravity if self-weight matters.
The most common convention in US undergraduate statics (Hibbeler, Beer and Johnston): positive x to the right, positive y upward, positive moments counterclockwise. Establish your coordinate axes at the start and stay consistent.
Problem: A 15 kg block rests on a 30-degree incline, held in place by friction. Find the normal force and the friction force.
Step 1. Isolate the block. Draw a rectangle representing the block. Remove the incline and replace it with the forces it exerts on the block.
Step 2. Draw weight W = mg = 15 x 9.81 = 147.15 N downward from the center using the Arrow tool. Label it W.
Step 3. Draw the two contact forces from the incline: normal force N perpendicular to the surface, and friction F along the surface pointing up the slope, since the block would otherwise slide down.
Step 4. The block is at rest, so it is in equilibrium. Tilt your coordinate system so x runs along the slope and y perpendicular to it. Sum of forces in y: N = W cos(30) = 147.15 x 0.866 = 127.4 N. Sum of forces in x: F = W sin(30) = 147.15 x 0.5 = 73.6 N.
| Setup | Forces to include | Notes |
|---|---|---|
| Block on flat surface | Weight down, normal up, friction horizontal | Friction opposes motion or tendency to move |
| Hanging mass (cable) | Weight down, tension up along cable axis | Cable tension equals weight at equilibrium |
| Simply supported beam | Applied loads, pin reaction (Rx, Ry), roller reaction (Ry only) | Pin carries horizontal and vertical; roller carries vertical only |
| Cantilever beam | Applied loads, fixed-wall reactions (Rx, Ry, moment M) | Fixed support provides moment resistance; pin and roller do not |
| Shaft under torque | Applied torques, bearing reactions, any transverse loads | Use Cyl Torque arrows to show torque direction along the shaft axis |
| Truss joint | Member forces along each axis, applied load if any | Assume tension positive; compression comes out negative |
Most courses expect them, especially if you tilt them to align with an inclined surface. Draw two short arrows with the Arrow tool and double-click each one to label it x or y.
Yes. On narrow screens the tools move to a bar along the bottom of the screen and the style controls collapse into a panel above it. Draw with one finger, pinch with two fingers to zoom and pan, and double-tap any shape to label it. A torque arc can be flipped with the on-screen Flip button. A mouse is still quicker for fine placement, but the tool is fully usable on a phone.
This tool has proper force arrow symbols, moment arcs, and 3D cylinder shapes built in. The PNG export is cropped to the drawing on a white background, so it pastes into a report without a slide around it, and SVG export stays sharp at any size.