Home / Topics / Newton's Laws & Forces
Free-body diagrams
Beginner
Sketch all forces on one body to apply Newton's laws.
Draw the body alone as a dot and draw every force acting on it with arrows, then choose axes and write ΣF = ma for each. Include only forces on that body, not forces it exerts.
A block on a slope: weight, normal, friction; resolve along and perpendicular to the slope.
Do not draw the acceleration or "force of motion" as a force.
In more detail
A free-body diagram shows only the forces acting on one object, drawn as arrows from its centre. It is the first step in solving most dynamics problems.
Real-world uses
- Structural engineers draw free-body diagrams to check forces in beams and joints.
- Physics exams award marks for correct free-body diagrams before any calculation.
- Engineers draw free-body diagrams for every component of a crane to check that the support forces balance the loads.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Should I include forces the object exerts on others?
No. Include only forces acting on the object itself.
What forces are commonly missed?
Normal force, friction and tension are often forgotten, especially on inclines and with pulleys.
What should I include in a free-body diagram?
Every force acting on the body, such as weight, normal, tension and friction, and nothing that the body exerts on other objects.
Related topics in Newton's Laws & Forces
Units of force · Newton's third law · Weight and normal force · Net force and equilibrium · Tension · Atwood machine