Force Calculator
Calculate force from mass and acceleration (F = ma).
Try an example
98
About this calculator
What Is Force?
In physics, a force is a push or a pull that can change an object's motion — start it moving, stop it, speed it up, slow it down or change its direction. Forces are measured in newtons (N) in the SI system, where one newton is the force needed to accelerate a one-kilogram mass at one meter per second squared. This force calculator applies Newton's second law to find force, mass or acceleration when you know the other two.
Newton's Second Law
F = m × a — force equals mass times acceleration. Rearranged, m = F ÷ a and a = F ÷ m. A 10 kg object accelerating at 3 m/s² needs a net force of 30 N. The same force on a 20 kg object produces only half the acceleration, which is why heavier things are harder to get moving.
Worked Example
The default values — 10 kg at 9.8 m/s² — show the force of gravity on a 10 kg object near Earth's surface: 98 newtons, which is that object's weight. (9.8 m/s² is standard gravitational acceleration on Earth.)
Net Force Is What Matters
The "F" in the law is the net force: the sum of all the forces on the object. If you push a box with 30 N and friction pushes back with 10 N, the net force is 20 N, and that is what produces the acceleration. When all forces cancel, the net force is zero and the object keeps moving at a constant velocity (or stays at rest) — Newton's first law.
Common Units
- Newton (N): 1 kg·m/s².
- Kilonewton (kN): 1,000 N, used in engineering.
- Pound-force (lbf): about 4.448 N.
- Dyne: 10⁻⁵ N, from the older CGS system.
Weight Is a Force Too
Weight is the gravitational force on a mass: W = m × g, where g ≈ 9.81 m/s² on Earth. A 70 kg person weighs about 687 N. Mass stays the same everywhere, but weight changes with gravity — on the Moon the same person weighs roughly one-sixth as much.
Related Calculators
Forces feed into other quantities: multiply a force by a distance to get work in the Work and Energy Calculator, or divide it by an area to get stress in the Pressure Calculator.
Worked example
A 10 kg object accelerating at 9.8 m/s² (Earth's gravity) experiences 98 newtons of force — its weight, about 22 lbf.
Frequently asked questions
What is Newton's second law?
Force equals mass times acceleration (F = ma) — the more mass an object has, or the faster it accelerates, the more force is required.
Why does the default use 9.8 m/s²?
That's the standard acceleration due to gravity near Earth's surface, so this default shows the force of gravity on a 10 kg object — its weight.
What's the difference between mass and weight?
Mass is constant everywhere; weight is the force of gravity on that mass, so it changes depending on which planet (or acceleration) you use.
What units does this use?
Mass in kilograms, acceleration in m/s², force in newtons (kg·m/s²) — with a pound-force (lbf) conversion shown alongside.
