Build a free body diagram, then drag it around.
Toggle forces on and off, adjust their magnitudes with sliders, and drag anywhere on the diagram to rotate the view. Hover any arrow to see what it represents.
Toggle a force, drag the view, read the result.
Everything updates instantly — no equations to type, no forms to submit.
Pick a scenario
Choose a preset from the dropdown — a block at rest, a block being pushed, pulled at an angle, sliding with friction, or falling.
Toggle forces on and off
Click any force card to add or remove that vector from the diagram. Weight, normal, friction, and applied force can each be shown or hidden.
Adjust magnitudes and angles
Use the sliders to change force strengths and the applied force angle. The arrows grow and shrink, and the net force readout recalculates live.
Spin and zoom the diagram
Drag anywhere on the stage to rotate the view, scroll or pinch to zoom, and hover any arrow to see its label and value.
What each arrow means.
A free body diagram isolates one object and shows every external force acting on it.
Weight (W or Fg)
Always points straight down toward the center of the Earth. Its magnitude equals the object's mass times gravitational acceleration (about 9.8 m/s² near Earth's surface).
Normal force (N or Fn)
Pushes perpendicular to the surface the object rests on. On a flat horizontal surface with no other vertical forces, it equals the weight. If you pull upward, the normal force decreases.
Friction (f)
Acts parallel to the surface and always opposes the direction of sliding (or intended sliding). Its maximum size depends on the normal force and the coefficient of friction between the surfaces.
Applied force (Fapp)
Fapp,y = F · sin θ
Any push or pull from outside the system. When applied at an angle, it splits into a horizontal component that drives motion and a vertical component that changes the normal force.
Net force (ΣF)
The vector sum of all forces. When the net force is zero, the object is in equilibrium — either at rest or moving at constant velocity. When it's nonzero, the object accelerates.
Newton's second law
The acceleration of the object is directly proportional to the net force and inversely proportional to its mass. This is the core link between the diagram and the motion.
Questions people actually ask.
The short answers — with the long ones one tap away.
What is a free body diagram?+
A free body diagram is a simplified drawing of a single object with every external force acting on it drawn as an arrow. The object is isolated from its surroundings, and each arrow shows the direction and relative magnitude of one force — weight, normal force, friction, tension, applied force and so on.
What forces act on a block sitting on a flat surface?+
A block resting on a horizontal surface has at least two forces: its weight pulling straight down and the normal force from the surface pushing straight up. If something pushes or pulls it sideways, an applied force appears, and if it slides or tries to slide, a friction force acts opposite to the motion.
How do you find the net force from a free body diagram?+
Break each force into horizontal and vertical components, add the components in each direction separately, then combine the two totals with the Pythagorean theorem. Net force equals mass times acceleration, so a zero net force means the object is in equilibrium — either at rest or moving at constant velocity.
What is the difference between weight and normal force?+
Weight is the gravitational pull on the object and always points straight down. Normal force is the perpendicular push from the surface the object rests on. On a flat surface with no other vertical forces they are equal in size, but they are not a Newton's third law pair — they act on the same object and come from different sources.
Why does friction oppose motion?+
Friction is the resistance between two surfaces in contact. It always acts parallel to the surface and opposite to the direction the object is sliding, or would slide if the surfaces were frictionless. Its size depends on how hard the surfaces are pressed together and on the roughness of the materials.
What does equilibrium mean on a free body diagram?+
Equilibrium means the net force is zero, so all the arrows on the diagram cancel out. The object is either stationary or moving at a constant velocity. On a free body diagram this shows up as the horizontal arrows matching each other and the vertical arrows matching each other.
Is this free body diagram tool free, and where does my data go?+
It's completely free and runs entirely in your browser — nothing you build or click is uploaded, logged, or sent to any server. No account, no sign-up, no limits.