Force
Apply Newton's second law or estimate net force. Free online calculator with formulas and step-by-step solutions.
Key formula
F = ma
How do you calculate force?
Net force is F = m × a. Multiply mass (kg) by acceleration (m/s²) to get newtons. Rearrange to a = F/m or m = F/a. Weight near Earth is W = mg, a special case with a = g.
About this tool
Newton’s second law links net force to mass and acceleration. This page keeps F = ma visible so you can solve for force, mass, or acceleration without mixing kilograms, newtons, and weight.
How to use this calculator
- Choose the variable you want to solve for and confirm which values are already known.
- Enter inputs in consistent units before calculating so the formula is applied correctly.
- Check whether the result is physically reasonable by comparing it with the size of the inputs.
- Use the step-by-step breakdown to see how the equation was rearranged and evaluated.
Worked examples
Example 1: 4.0 kg at 2.5 m/s²
F = m a = (4.0)(2.5) = 10 N in the direction of the acceleration.
Example 2: find acceleration
F = 36 N, m = 6.0 kg. a = F/m = 36/6.0 = 6.0 m/s².
Example 3: find mass
F = 24 N, a = 3.0 m/s². m = F/a = 24/3.0 = 8.0 kg.
Frequently asked questions
What is the force formula?
Newton’s second law: F = m a. Mass in kg, acceleration in m/s², force in newtons. Rearrangements are a = F/m and m = F/a.
Is F the applied force or the net force?
F in F = ma is the net force — the vector sum of all forces on the object. Friction, tension, and gravity must be included before you apply F = ma.
What is the difference between mass and weight?
Mass (kg) measures inertia. Weight (N) is the gravitational force W = mg. Do not put weight in newtons into the m slot of F = ma.
How does F = ma relate to centripetal force?
For circular motion, a = v²/r toward the centre, so F = m(v²/r) = mv²/r. Use the centripetal force calculator when the path is a circle.
How does force relate to momentum and work?
Impulse J = FΔt equals Δp. Work W = Fd transfers energy when force acts through a displacement. Use the momentum and work calculators for those forms.