Parallelogram of forces
3 N plus 4 N doesn't always make 7 N.
Force is a vector, and forces combine according to the parallelogram rule: draw a parallelogram with the two component forces as adjacent sides, and its diagonal is the resultant. The larger the angle between the two forces, the smaller the resultant; it is largest when they point the same way (F₁ + F₂) and smallest when they point in opposite directions (|F₁ − F₂|). Conversely, a single force can be resolved into two components using a parallelogram.
This is a static model: forces and the graph update as soon as you change a parameter.
Resultant vs. angle between forces
As the angle increases from 0° to 180°, the resultant decreases from F₁ + F₂ to |F₁ − F₂|.
Think about it
Two forces of 3 N and 4 N: at what angle between them is the resultant exactly 5 N?
90°. When the two forces are perpendicular, the resultant is the hypotenuse of a right triangle: √(3² + 4²) = 5 N. Set F₁ to 4 N, F₂ to 3 N and the angle to 90° to check.
Model assumptionsTwo concurrent forces in the same plane · Resultant found by the parallelogram rule
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.