Draw a free body diagram the way physics is really done — one object, every force on it as an arrow, added up as vectors. Load a classic scenario (a block on the ground, a block on a frictionless incline, a sign hanging from two ropes, a box pushed against friction, an accelerating elevator) or add your own forces, then drag any arrowhead to change its size and direction. A live panel resolves the forces into ΣFx, ΣFy and the resultant, tells you whether the body is in equilibrium, and gives the acceleration from a = Fnet/m. It all runs on your device.
You are in the Physics lab.
What every coloured arrow, the dashed resultant and the readout panel are telling you.
Every arrow starts at the body and points the way that force pushes or pulls, with a length that stands for its size in newtons — and its label sits just beyond the head. The colours are fixed by type: amber is weight (gravity, straight down), blue is the normal force from a surface, purple is friction along a surface, green is rope tension, and orange is an applied push or pull. Reading the colours tells you which forces are in play before you add a single number.
The bold white dashed arrow is the net force — the vector sum of every coloured arrow — labelled Fnet in newtons. When the forces cancel it disappears and a green ⚖ In equilibrium — ΣF = 0 badge shows at the top of the stage, matched by the In equilibrium? readout turning to Yes. When they do not cancel, the dashed arrow points the way the body is pushed, and ΣFx, ΣFy, |Fnet| and its direction in the panel give it in numbers.
Newton's second law turns that resultant into motion: divide the net force by the mass and you get the acceleration, pointing the same way as the dashed arrow. The Acceleration a = F/m readout does this live for the mass on the slider, so a balanced body reads 0.00 m/s² while an unbalanced one accelerates — raise the mass and the same net force yields a gentler acceleration.
Isolate the body, draw every force, then add the arrows as vectors.
A free body diagram shows one object and nothing else — just the external forces acting on it, each drawn as an arrow from the body in the direction it pushes or pulls, with a length that stands for its size. Load a scenario to see a correct set of forces, or press Add force to place your own. Weight, the normal force, tension, friction and applied pushes each get their own colour.
Drag an arrowhead to change a force's magnitude and direction at once, or select it and use the magnitude and direction sliders for precision. As you do, the tool resolves every force into horizontal and vertical components and adds them, so the numbers update the instant an arrow moves.
The dashed white arrow is the net force — the vector sum of everything else. The panel shows ΣFx, ΣFy, the size and direction of Fnet, whether the body is in equilibrium, and the acceleration a = Fnet/m for the mass you set. Balance the arrows and the resultant vanishes; unbalance them and it points the way the body accelerates.
Teaching or blogging about mechanics? You can embed this tool on your own site free — one line of code, no sign-up.
A ready-to-assign lab using the simulation above. Free to use — nothing to install or sign up for, and no student data leaves the browser.
For each scenario, list the forces and their directions, then state the net force.
A free body diagram isolates one object and draws every force acting on it as a vector. Summing those vectors gives the net force, and Newton’s second law (a = F_net/m) turns it into the motion — the starting point for nearly every mechanics problem.
Educators: link or embed this simulation freely in your LMS or course guide.
Put the Free Body Diagram Maker on your own page — free, no sign-up, no watermark. It runs entirely in your visitors' browsers. Copy the snippet and paste it into your page's HTML.