Free Body Diagram Maker
Draw free body diagrams with every force an arrow from the body, labeled W, N, f or T, for inclines, friction, tension, pulleys and Atwood machines, elevators, circular motion and beams. For physics and statics.
Free body diagram examples
Real renders of the prompts shown: a block sliding down a 30° incline, a box pushed across the floor, a traffic light hung from two cables and a blank free body diagram worksheet. Click one to load and edit its prompt.
How to draw a free body diagram, shown on a block pulled up a slope
The labeled free body diagram here is a block pulled up a rough incline by a rope parallel to the surface. The same four steps work for any mechanics problem.
- 1
Shrink the body to a point
Every arrow starts at the dot in the middle of the block, tail on the body, even the pull of the rope.
- 2
Weight first, straight down
W = mg points toward the centre of the Earth, not into the slope.
- 3
Two forces from each surface
N perpendicular to the incline; kinetic friction f_k along it, down the slope because the block moves up.
- 4
Pulls, then tilted axes
F_applied along the rope; x along the slope and y perpendicular, so only W has to be split.
Free body diagram examples for the classic mechanics problems
Each setup has its own set of forces and its own best choice of axes. Describe the setup and say which object to isolate; these are the ones physics courses set most often.
Force diagram of a box on a level floor
The first one most courses teach. A box pushed to the right at constant speed has four forces: the push F_app to the right and friction to the left, equal; weight mg down and the normal force N up, equal. Constant speed means zero net force, so the arrows pair off. Push down at an angle θ below the horizontal and N grows to mg + F sin θ; pull up at the same angle and it shrinks to mg − F sin θ, so pulling meets less friction.
Free body diagram on an inclined plane
Weight mg straight down, the normal force perpendicular to the slope, friction along it. Tilt the axes: x down the slope, y perpendicular to it, and mg splits into mg sin θ along the slope and mg cos θ into it, so N = mg cos θ. A block at rest has static friction pointing up the slope, equal to mg sin θ; it starts to slide once tan θ is greater than μ_s.
Free body diagram with friction
Friction is always parallel to the surface. Kinetic friction f_k = μ_k N points against the sliding. Static friction points against the slip that would happen without it and can take any size up to μ_s N. A car speeding up is pushed forward by static friction on its driven tyres; a box on a braking truck is held by static friction pointing backward, against the truck's motion.
Free body diagram with tension
A hanging mass: tension T up the string, weight mg down; at rest or at constant velocity, T = mg. A traffic light on two cables at angles θ₁ and θ₂ to the horizontal: isolate the knot, draw T₁ and T₂ along the cables and the light's weight down. Then T₁ cos θ₁ = T₂ cos θ₂ horizontally and T₁ sin θ₁ + T₂ sin θ₂ = mg vertically. The third example render above is this setup.
Pulley and Atwood machine free body diagrams
One diagram for each mass, never one for the whole system. In an Atwood machine with a massless, frictionless pulley, each mass has tension T up and its own weight down, and T is the same on both sides. Taking positive in the direction the heavier mass m₂ moves, a = (m₂ − m₁)g / (m₁ + m₂) and T = 2m₁m₂g / (m₁ + m₂). For a block on a table tied over a pulley to a hanging mass, the block gets N, mg, T toward the pulley and friction, the hanging mass T and mg.
Elevator free body diagram
A person standing on a scale in a lift: weight mg down and the normal force N from the floor up — N is what the scale reads. With up as positive, N − mg = ma. Accelerating upward, N is larger than mg and the person feels heavier; accelerating downward, smaller; moving at constant speed in either direction, N = mg; in free fall, N = 0. For the lift car itself, draw the cable tension up and the total weight down.
Circular motion free body diagram
Draw only the real forces; the centripetal force is their net, pointing to the centre, and gets no arrow of its own. A car on a flat curve: mg down, N up, and static friction toward the centre, with f = mv²/r. A ball on a string in a horizontal circle (a conical pendulum): T along the string, mg down; the horizontal part of T points inward. At the top of a vertical loop, T and mg both point down.
Pendulum free body diagram
Two forces on the bob: tension T along the string toward the pivot and weight mg straight down. Use radial and tangential axes instead of x and y: mg sin θ along the arc pulls the bob back toward the bottom, and along the string T − mg cos θ = mv²/L. At the end of each swing the bob stops, so T = mg cos θ there; at the bottom T is at its largest.
Spring free body diagram
The spring force points along the spring, back toward its natural length, with size kx (Hooke's law). A mass hanging on a spring: kx up, mg down; at equilibrium kx = mg, which gives the stretch x = mg/k. A mass on a horizontal spring: the spring force is the only horizontal force, pulling back when the spring is stretched and pushing out when it is compressed, plus mg and N.
Free body diagram of a beam (statics and torque)
An extended body, so each force goes where it acts, not at one dot. A beam on two supports: reaction forces up at A and B, the beam's weight at its centre, any load where it hangs. A pin support gives a horizontal and a vertical reaction, a roller one perpendicular to its surface. Statics needs ΣF_x = 0, ΣF_y = 0 and Στ = 0; take torques about a support to drop its unknown. A ladder against a smooth wall works the same way: a horizontal push from the wall, N and friction at the floor, weight at the middle.
Forces on a free body diagram and how to draw each one
The forces that come up most often in mechanics problems, the symbol each is usually given, and the direction its arrow must point. These are the conventions every diagram here follows unless you ask for others.
| Force | Symbol | How to draw it |
|---|---|---|
| Weight (force of gravity) | W or mg (also F_g) | Straight down, toward the center of the Earth, on every object with mass |
| Normal force | N (also F_N) | Perpendicular to the contact surface, pushing away from it |
| Kinetic friction | f_k | Parallel to the surface, opposite to the direction of sliding |
| Static friction | f_s | Parallel to the surface, opposite to the way the object would start to slip |
| Tension | T | Along the rope, string or cable, pulling away from the body |
| Applied force | F_app (also F_a or P) | In the direction of the push or pull |
| Air resistance (drag) | F_air or D | Opposite to the object's velocity through the air |
| Spring force | F_spring | Along the spring, back toward its natural length |
Symbols vary between textbooks. Some courses write F_g and F_N, others W and N, and some write every force as F with a two-letter subscript naming who pushes on whom. Tell the maker which symbols your course uses and only those are drawn.
Free body diagram vs motion diagram: what is the difference?
A free body diagram shows the forces on one object at one instant; a motion diagram shows where the object is at equal time intervals, with its velocity and acceleration arrows. Mixing the two — adding a velocity arrow to a free body diagram — is one of the errors physics teachers mark down most often.
| Free body diagram | Motion diagram | |
|---|---|---|
| What it shows | The forces acting on one object | The object's position at equal time intervals |
| The arrows are | Forces, each exerted by something | Velocity and acceleration |
| The object is drawn | Once, as a dot or a simple box | Several times, as a row of dots |
| Arrow length | In proportion to the size of each force | In proportion to the speed or its change |
| Answers | Why does it move this way? (ΣF = ma) | How does it move? |
| Belongs on it | W, N, f, T, F_app | v and a |
Newton's second law links the two: the net force from the free body diagram points the same way as the acceleration on the motion diagram. If the arrows on your free body diagram cannot add up to the acceleration you expect, a force is missing or pointing the wrong way.
What is a free body diagram?
A free body diagram (FBD) shows one object on its own, drawn as a dot or a simple box, with every external force acting on it drawn as an arrow that starts on the object and points the way the force acts. Each arrow carries its symbol — W or mg for weight, N for the normal force, f for friction, T for tension — and the diagram is the first step in applying Newton's second law.
Key facts
- Only forces belong on it. Velocity, acceleration and the net force are not forces acting on the body, so they are not drawn; the net force is what you work out from the diagram.
- Every force needs something that exerts it. Weight comes from the Earth, the normal force and friction from a surface in contact, tension from a rope or cable. If nothing is pushing or pulling, there is no arrow — which rules out a “centrifugal force” in an ordinary, non-rotating frame.
- The normal force is perpendicular to the surface. On a level floor it points straight up; on an incline at angle θ it tilts with the surface, and with no other force pressing the block into the slope its size is mg cos θ, not mg.
- Friction is parallel to the surface. Kinetic friction points opposite to the direction of sliding; static friction points whichever way stops the object from starting to slip.
- Tilt the axes on an incline. With x along the slope and y perpendicular to it, only the weight has to be split into components: mg sin θ down the slope and mg cos θ into the surface.
Common questions about free body diagrams
What should a free body diagram include?
The object on its own as a dot or a simple box, one arrow for every external force acting on it, each labeled with its symbol, and a coordinate system. Nothing else — no surroundings, no velocity or acceleration arrows, no net force. That is the default; ask for the incline or the rope to be sketched in and they are.
Is a force diagram the same as a free body diagram?
In most courses, yes: both draw the forces on one object as arrows labeled with their symbols, and the two names are used for the same drawing. Where a course does separate them, a force diagram may show the object in its surroundings or several objects at once, while a free body diagram always isolates one object and nothing else. Either way, every arrow is a force exerted by something.
How do you draw a free body diagram step by step?
Isolate the object, find every force on it, then draw and label each as an arrow from the body. Start with its weight; add a normal force and friction for every surface it touches and a tension for every rope or cable; add any push or pull. Then choose axes — along and perpendicular to the surface on an incline — and check that every arrow has something exerting it.
Why is the normal force not vertical on an incline?
Because the normal force is always perpendicular to the surface that exerts it — and an incline's surface is tilted. Drawing it straight up is the most common free body diagram mistake. Its size changes too: with no other force pressing the block into the slope, N = mg cos θ, smaller than the weight.
Should I draw a centrifugal force for an object moving in a circle?
No. In the usual inertial frame nothing exerts a centrifugal force, so it has no arrow. The centripetal force is not an extra arrow either: it is the name for the net inward force made up of the forces already drawn — tension on a swinging ball, friction on a car in a bend, gravity on a satellite.
Do velocity and acceleration go on a free body diagram?
No — only forces do. A body moving to the right does not need a force to the right; a crate sliding at constant speed has balanced forces. If you want to show the direction of motion, write it beside the diagram, not as an arrow on it.
Which way does friction point?
Along the surface, opposite to the sliding. Kinetic friction opposes the motion of the object relative to the surface; static friction opposes the way it would start to slip, so on a block resting on a slope it points up the slope.
Where should the force arrows start?
On the object, pointing the way each force acts. In a particle diagram every arrow starts at the dot or the center of the box — even a push is drawn tail on the body. When turning effects matter, as for a beam or a ladder, draw each force at the point where it acts.
Does it calculate the forces, like a free body diagram solver?
It draws the diagram; the equations stay yours. Give it the numbers — the mass, the angle, a coefficient of friction — and they are written on the drawing, but it does not solve for unknown forces, so check any value before you rely on it.
Keep exploring
Our other diagram tools, and the guides behind them.
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