This force calculator applies Newton’s second law, F = m × a. Solve for force, mass or acceleration — enter the two values you know and get the third, in newtons.
What Is Force? (Newton’s Second Law)
Force is a push or pull measured in newtons, and Newton’s second law defines it: F = m × a — the net force on an object equals its mass times its acceleration. It is the most-used equation in mechanics: it explains why heavy things are hard to shove, why seatbelts matter, and how rockets are sized. This calculator is part of our Physics Calculators collection.
Worked Example (Verified)
A 10 kg object accelerating at 9.8 m/s²: F = 10 × 9.8 = 98 N. That example is no coincidence — gravity accelerates everything at ~9.8 m/s² on Earth, so an object’s weight (the gravitational force on it) is F = m × 9.8: a 70 kg person weighs about 686 N (even though their mass is 70 kg everywhere in the universe). Mass is intrinsic; weight is a force and changes with gravity — the same person weighs ~114 N on the Moon.
Force Intuition
- 1 newton ≈ the weight of a small apple (102 g) in your hand.
- A car pushing: accelerating a 1,200 kg car at 3 m/s² needs 3,600 N of net force at the wheels.
- Braking: stopping that car at −8 m/s² means the brakes and tires exert ~9,600 N — deceleration is acceleration with a sign.
- Net force: F = ma uses the sum of all forces. A book resting on a table has gravity and the table’s normal force canceling — net force zero, acceleration zero.
Force applied over a distance does work and changes kinetic energy — the bridge to our Kinetic Energy Calculator.
Related Tools
- Kinetic Energy Calculator — KE = ½mv²
- Density Calculator
- Physics Calculators — the full collection
Frequently Asked Questions
What is the unit of force?
The newton (N): 1 N = 1 kg·m/s² — the force that accelerates 1 kg by 1 m/s². In imperial units, 1 N ≈ 0.225 pounds-force (lbf).
What is the difference between mass and weight?
Mass (kg) is how much matter an object has and never changes. Weight is the gravitational force on that mass (newtons) and depends on local gravity.
How do I find acceleration from force?
a = F ÷ m. Choose “Acceleration” above — a 500 N net force on a 50 kg object gives 10 m/s².
What acceleration does gravity produce?
About 9.8 m/s² near Earth’s surface (exactly 9.80665 by definition for standard gravity), regardless of the object’s mass — Galileo’s insight.
Is friction a force?
Yes — it opposes motion and is part of the net force. A pushed box that does not accelerate has friction exactly balancing your push.
Is this force calculator free?
Yes — free, instant, no sign-up.