What this calculator does
Net force is what is left once every force acting on an object along a line is added together, accounting for direction. An object pushed one way with 100 N and pulled the opposite way with 40 N does not experience 140 N: the two partly cancel, leaving a net force of 60 N in the direction of the larger push.
This calculator adds up to four forces acting along a single axis, treating one direction as positive and the opposite direction as negative, then reports the resultant net force. Given a mass as well, it also works out the acceleration that net force produces, using Newton's second law.
The formula
Enter each force as a signed number: positive for one direction along the line, negative for the opposite direction. Adding them gives the net force. If the forces exactly cancel, the object is in equilibrium and the net force is zero, meaning no change in its motion. With a mass entered, dividing the net force by that mass gives the resulting acceleration.
| Term | Meaning |
|---|---|
| Net force | The single resultant force left after every individual force along the line is added together, respecting sign. |
| Equilibrium | The state where the net force is zero, so the object's velocity does not change. |
| Acceleration | The rate of change of velocity the net force produces on a given mass: a = F_net / m. |
The inputs explained
| Field | What to enter |
|---|---|
| Force 1 (positive one way, negative the other) (N) | The first force acting on the object. Use a positive number for one chosen direction. |
| Force 2 (N) | A second force. Use a negative number if it acts in the opposite direction to force 1. |
| Force 3 (N) | A third force, if there is one. Leave at zero if not needed. |
| Force 4 (N) | A fourth force, if there is one. Leave at zero if not needed. |
| Mass of the object (0 to skip acceleration) (kg) | The mass of the object, to calculate the resulting acceleration. Leave at zero to skip this. |
When to use it
Tug-of-war and opposing pulls
Two or more forces pulling in opposite directions, such as a rope being pulled from both ends, are a direct case for signed forces along one line: whichever side pulls harder determines the direction of the net force and which way the object actually moves.
A vehicle with drive and drag forces
A car's engine pushes it forward while air resistance and rolling friction push back. The net of those forces, divided by the car's mass, gives its actual acceleration, which is always less than what the engine force alone would suggest.
Checking whether an object is in equilibrium
A stationary or constant-velocity object has zero net force acting on it by definition. Adding up the known forces and confirming they sum to zero is a standard check in introductory mechanics problems.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How net force and acceleration change with an opposing force
A fixed 100 N applied force and a 20 kg mass, against a growing opposing force.
| Opposing force | Net force | Resulting acceleration (F_net / m) |
|---|---|---|
| 0 N | 100.00 N | 5.000 m/s² |
| -20 N | 80.00 N | 4.000 m/s² |
| -40 N | 60.00 N | 3.000 m/s² |
| -60 N | 40.00 N | 2.000 m/s² |
| -80 N | 20.00 N | 1.000 m/s² |
| -100 N | 0.00 N | 0.000 m/s² |
How acceleration changes with mass at a fixed net force
A fixed 60 N net force (two 60 N forces in the same direction, no opposing force), across a range of masses.
| Mass | Net force | Resulting acceleration (F_net / m) |
|---|---|---|
| 5 kg | 120.00 N | 24.000 m/s² |
| 10 kg | 120.00 N | 12.000 m/s² |
| 20 kg | 120.00 N | 6.000 m/s² |
| 40 kg | 120.00 N | 3.000 m/s² |
| 60 kg | 120.00 N | 2.000 m/s² |
| 120 kg | 120.00 N | 1.000 m/s² |
Questions
What if my forces do not act along a single line?
This calculator handles forces along one axis, added with sign. Forces at an angle to each other need to be broken into components along perpendicular axes first (for example horizontal and vertical), with each axis summed separately, before the two resultant components are combined.
What does a net force of zero actually mean?
It means the object is in equilibrium: the forces acting on it exactly balance, so there is no acceleration. The object is not necessarily at rest, it could be moving at a constant velocity, since zero net force means no change in motion, not necessarily no motion at all.
How is this different from a basic force calculator?
A basic force calculator such as the force, mass and acceleration calculator starts from a single force (or works out force from mass and acceleration). This calculator starts from several separate forces acting on the same object and combines them into one net result first.
Why enter mass separately rather than always showing acceleration?
Net force by itself is a complete answer for many problems, such as checking equilibrium. Acceleration only makes sense once a mass is specified, so it is left optional rather than assuming a default mass that may not apply to your situation.
For a single force from mass and acceleration directly, see the force, mass and acceleration calculator. For gravitational attraction between two masses specifically, see the Newton's law of universal gravitation calculator.