Build a free-body diagram, then drag it around.
Pick a preset or add forces one at a time. Drag the block to move it, rotate vectors, zoom in and out, and hover any arrow to see what it represents.
Everything responds to a click or a drag.
The whole diagram is the interface — no menus to dig through.
Pick a scenario
Choose a preset like a block on a table, a pushed block, or a hanging mass — the diagram builds itself with the right forces.
Add or remove forces
Use the steppers to increase or decrease gravity, normal, friction, tension, and applied force and watch the arrows grow or shrink live.
Drag and rotate
Drag the block to move it around the stage, drag the tip of any arrow to rotate its direction, and scroll to zoom in and out.
Hover to identify
Hover any vector arrow to see its name, magnitude, and angle — and watch the net force readout update as you build.
What you're actually looking at.
Each arrow is a force — its length is the magnitude and its direction is the push or pull.
Gravity (weight)
The amber arrow pulls the block toward the centre of the Earth. Its magnitude is the mass times the gravitational field strength, and it never disappears in a free-body diagram.
Normal force
The teal arrow is the surface pushing back on the block. On a flat table it points straight up and usually balances gravity exactly when the block is not accelerating vertically.
Friction
The amber-deep arrow always points opposite to the direction the block would slide. It is zero when there is no attempt to move, and grows until it reaches its maximum value.
Questions people actually ask.
The short answers — with the long ones one tap away.
What is a force diagram?+
A force diagram — also called a free-body diagram — shows a single object isolated from its surroundings with every force acting on it drawn as an arrow. The length of each arrow is proportional to the size of the force and the arrow points in the direction the force pushes or pulls.
What is net force?+
Net force is the single force you get when you add all the individual force vectors together. If the net force is zero the object stays at rest or moves at constant velocity; if it is not zero the object accelerates in the direction of the net force according to F = ma.
What are the common forces on a block?+
The usual suspects are weight (gravity pulling down), normal force (the surface pushing up perpendicular to it), friction (opposing sliding along the surface), tension (a rope or string pulling), and any applied force you push or pull with.
How do you add forces that are not along the same line?+
You break each force into horizontal and vertical components, add the components separately, then combine the totals with the Pythagorean theorem. The direction of the net force comes from the inverse tangent of the vertical sum over the horizontal sum.
What happens when the net force is zero?+
When all forces balance the object is in equilibrium: it either stays still or keeps moving at a constant velocity in a straight line. There is no acceleration, which is why a book resting on a table does not sink or float.
Is this force diagram tool free and private?+
It is completely free and runs entirely in your browser — nothing you build or drag is uploaded, logged, or sent to a server. No account, no sign-up, no limits.