Newton's Second Law Calculator
Newton's Second Law calculator (F = ma): solve for force, mass or acceleration in SI units, with a US/imperial readout. Curriculum-aligned.
Newton's Second Law Calculator
Enter any two values and leave the third blank — the calculator solves for it. Results are in SI units, with a US/imperial readout below.
- Curriculum
- English (Singapore) — Singapore Examinations and Assessment Board (SEAB)
- Built against
- SEAB GCE O-Level Pure Physics 6091 (2023–2026)
- Unit system
- SI primary; US/imperial readout below
- First published
- 1 Jun 2026
- Last updated
- 1 Jun 2026
View authoritative scientific sources
- NIST SP 811 (2008), §3 — units & conversions
- BIPM SI Brochure, 9th edition (2019)
- CODATA 2018 recommended values
- Newton's Laws of Motion — Encyclopædia Britannica
⚠️ Educational use only — see full disclaimer
EDUCATIONAL USE DISCLAIMER
This calculator is provided for educational and reference purposes only. It is not a substitute for instruction from a qualified teacher, your prescribed textbook, or your school's official curriculum materials.
When preparing for examinations, always cross-check our calculations and notation against your current syllabus and your teacher's guidance. Syllabus conventions and accepted notation vary between curricula and may change between examination years.
If you believe any calculation, notation, or curriculum reference in this tool is inaccurate, please let us know via the feedback button. We review feedback promptly and update tools when verified corrections are needed.
RECATOOLS accepts no liability for academic, examination, professional, or research outcomes arising from use of this tool.
How to Use the Newton's Second Law Calculator
Pick your curriculum
Use the curriculum pills above to match your syllabus. Terminology, the worked example and the whole page follow your selection.
Enter any two values
Type two of force, mass and acceleration — leave the one you want to find blank. Each field has a unit selector; pick kg or lb, N or lb-f, m/s² or g.
Read the SI result
The answer is shown in SI units (the standard every syllabus teaches), with a dimmed US/imperial readout below that you can hide.
Check against your syllabus
The Tool Information block shows exactly which syllabus this is built against. Spot something off? Use the feedback button — we review every report.
Newton's Second Law, in Your Curriculum's Words
Newton's Second Law of Motion
Worked example (SEAB style): An MRT train of mass 50 000 kg accelerates from rest at 0.8 m/s². Calculate the net force.
Given: m = 50 000 kg, a = 0.8 m/s²
Applying F = ma:
F = 50 000 × 0.8 = 40 000 N = 4.0 × 10⁴ N
Newton's second law states that the net force on an object equals its mass times its acceleration: F = ma. Force is in newtons (N), mass in kilograms (kg), acceleration in metres per second squared (m/s²) — the SI units the SEAB syllabus uses throughout. Rearranged, the same law gives mass (m = F / a) or acceleration (a = F / m).
SEAB Pure Physics teaches mechanics in SI, so SI is always the primary result. We add a dimmed US/imperial readout for reference. All calculation happens in your browser — nothing is uploaded.
One newton is the force that gives a one-kilogram mass an acceleration of one metre per second squared. The law is the same everywhere; only the words around it change.
10 Facts About Newton's Second Law
F = ma is the second of Newton's three laws of motion, published in 1687.
One newton accelerates a 1 kg mass at 1 m/s² — the SI definition.
The law is about net force — the sum of all forces on the object.
More precisely, force is the rate of change of momentum, F = dp/dt.
Double the force and acceleration doubles; double the mass and it halves.
Weight is just F = mg — mass times gravity (9.81 m/s²).
Every curriculum from IGCSE to 高考 teaches this law in SI units.
In imperial units the force unit is the pound-force (1 N ≈ 0.2248 lb-f).
The law holds only in an inertial frame — one not itself accelerating.
This calculator runs in your browser — your working stays private.
Frequently Asked Questions
- F = ma — net force equals mass times acceleration. Rearranged, m = F / a and a = F / m. This calculator solves for whichever of the three you leave blank.
- SI units: newtons (N), kilograms (kg), metres per second squared (m/s²). You may enter other units (lb, oz, lb-f, ft/s², g); the tool converts to SI internally and shows the result in SI with a US/imperial readout.
- Yes. Enter any two of force, mass and acceleration and leave the third blank — the calculator rearranges F = ma and solves for the missing value.
- The physics — F = ma in SI units — is identical worldwide. What changes is the terminology, worked-example style and exam conventions. The selector matches those to your syllabus so the tool reads like your textbook.
- The smaller of your inputs' significant figures, capped at five, switching to scientific notation for very large or very small numbers — standard exam practice.
- Weight is a specific force — gravity on a mass — given by F = mg with g ≈ 9.81 m/s². To find weight, enter the mass and use g as the acceleration.
- The Tool Information block lists the exact syllabus for your selected curriculum (e.g. SEAB Pure Physics 6091 or SPM Fizik 4531). It is a study aid, not a substitute for your official syllabus or teacher.
- Use the "Spot an inaccuracy?" feedback button in the Tool Information block. Tell us the issue and your curriculum; we review every report and correct verified issues.
- No. Every calculation runs in your browser; nothing you type is uploaded. It works offline once the page has loaded.
- Completely free, no account or usage limit. It runs entirely in your browser and collects no data.
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