What is a Newton in everyday terms?

About the weight of a medium apple (roughly 100 g × 9.81 ≈ 0.98 N). The force you feel when holding a 100 g object.

What is the difference between mass and weight?

Mass (kg) is the amount of matter in an object. Weight (N) is the gravitational force on it. Your mass is the same on the Moon, but your weight is about 1/6 of what it is on Earth.

What is Newton's First Law?

An object at rest stays at rest, and an object in motion stays in motion, unless acted upon by a net force. The Second Law tells you what happens when a net force exists.

What is Newton's Third Law?

For every action, there is an equal and opposite reaction. Push a wall with 100 N and the wall pushes back with 100 N.

How do I find acceleration if I know force and mass?

Rearrange: a = F / m. If a 500 N force acts on a 50 kg object, a = 500/50 = 10 m/s².

What is gravitational acceleration on other planets?

Moon: 1.62 m/s². Mars: 3.72 m/s². Jupiter: 24.79 m/s². Earth: 9.81 m/s².

Force Calculator: Newton's Second Law

Mass

Enter 0 to calculate

Acceleration

m/s²

Enter 0 to calculate. Gravity = 9.81 m/s²

Formula

F = m × a

Force (N) = Mass (kg) × Acceleration (m/s²). 1 Newton = 1 kg·m/s². Earth's gravitational acceleration is 9.81 m/s².

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TL;DR

Enter mass and acceleration to calculate force in Newtons. Uses F = m × a.

Enter mass in kilograms and acceleration in m/s² to get force in Newtons. The calculator also rearranges Newton's second law to find mass from force and acceleration, or acceleration from force and mass. Earth's gravitational acceleration is 9.81 m/s² if you need it.

Newton's Second Law states that the net force on an object equals its mass times its acceleration (F = ma). This is one of the most fundamental equations in physics. Use it to find the force needed to accelerate an object, the weight of an object under gravity, or to analyze motion problems.

You came here because

Common situations

Weight calculation: Weight = mass × 9.81 m/s². A 70 kg person weighs 686.7 N.
Vehicle dynamics: Calculate the force needed to accelerate a car at a given rate.
Structural engineering: Determine forces on beams and supports under load.
Physics homework: Solve mechanics problems involving F = ma quickly.

Under the hood

How the calculation works

1Enter mass in kilograms.
2Enter acceleration in m/s². For weight under gravity, use 9.81 m/s².
3The calculator multiplies mass by acceleration to get force in Newtons.
4Kilogram-force (kgf) conversion is also shown for practical reference.

Show me

A real example

Example: A 2,000 kg car accelerates at 3 m/s²

1F = m × a
2F = 2000 kg × 3 m/s²
3F = 6,000 N
4In kgf: 6000 / 9.81 ≈ 611.6 kgf

Result: 6,000 N net force required

Watch out for

What can go wrong

Using weight in Newtons as mass in kg: A 70 kg person weighs about 686 N on Earth (70 × 9.81). If a problem gives you weight in Newtons, divide by 9.81 to get mass in kg before using the force formula.
Forgetting to account for direction: Force is a vector quantity. The formula F = ma gives magnitude. In problems involving multiple forces or angles, you need vector addition, not just this simple product.
Using non-SI units without converting: If mass is in pounds or acceleration in ft/s², the result will not be in Newtons. Convert to kg and m/s² first. 1 lb = 0.4536 kg; 1 ft/s² = 0.3048 m/s².
Confusing gravitational acceleration with applied acceleration: Earth's gravitational acceleration (9.81 m/s²) is the specific acceleration due to gravity. For other types of motion, use the actual acceleration of the object, not this constant.

Glossary

Related concepts

Term	Definition
Newton (N)	SI unit of force. 1 N = 1 kg·m/s². The force that accelerates a 1 kg mass at 1 m/s².
Newton's Second Law	F = ma. Net force equals mass times acceleration. The direction of force equals the direction of acceleration.
Weight vs mass	Mass is constant (kg). Weight is the gravitational force on that mass (N = kg × 9.81). They are different.
Inertia	The resistance of an object to changes in its motion. Greater mass means greater inertia, making the object harder to accelerate or decelerate.

Make it better

Pro tips

Rearrange for mass or acceleration: The calculator solves for force, mass, or acceleration depending on which two values you know. Use it to find required acceleration given a force limit, or required mass to produce a target force.
Use g = 9.81 m/s² for Earth gravity problems: For objects falling or resting on a surface, the acceleration is 9.81 m/s². Multiplying mass by 9.81 gives the gravitational force (weight) in Newtons.
Check your answer with units: Force in Newtons = kg × m/s². If your units do not cancel to N, you have a unit mismatch. Always verify unit consistency in physics calculations.
Apply to friction and tension problems: Friction force = coefficient × normal force. Normal force on a flat surface = mass × g. This calculator handles the core F = ma step; combine with a friction coefficient separately.

Common questions

Frequently asked questions

For related calculations, try the Density Calculator, or Ohm's Law Calculator. Browse all Calculator Online calculators for the full catalog.

Methodology

This calculator uses the standard force calculator formula. Results match those from established financial, scientific, and health references.

Reviewed by

Calculator Online Editorial Team. All formulas verified against authoritative sources before publication.

Last updated

2026-01-15