What is Newton's Second Law?

Newton’s Second Law of Motion states that the net force acting on an object equals its mass multiplied by its acceleration: F = m × a. Rearranged: m = F / a and a = F / m.

What units does this calculator support?

Metric: Newtons (N) for force, kilograms (kg) for mass, metres per second squared (m/s\xc2\xb2) for acceleration. Imperial: pound-force (lbf) for force, pounds-mass (lb) for mass, feet per second squared (ft/s\xc2\xb2) for acceleration.

Can I mix metric and imperial values?

No. This calculator requires all values in the same unit system. Select either metric or imperial before entering values to ensure consistent results.

What is the difference between pounds-mass (lb) and pound-force (lbf)?

In the imperial system, mass is measured in pounds-mass (lb) and force in pound-force (lbf). F = ma still holds, but the gravitational constant (g = 32.174 ft/s\xc2\xb2) links them. This calculator treats the relationship directly: F (lbf) = m (lb) \xc3\x97 a (ft/s\xc2\xb2) / 32.174.

How many significant figures does the result use?

Results are displayed to 4 significant figures, which is appropriate for most physics and engineering problems.

Newton's Second Law Calculator

Name: Newton's Second Law Calculator
Availability: InStock
Author: Nham Vu

Enter any two of force (F), mass (m), or acceleration (a) to instantly solve for the third using Newton’s Second Law: F = m × a.

Enter Two Known Values

Unit System

Solve For

Force — F (N)

Mass — m (kg)

Acceleration — a (m/s²)

m/s²

Results

Select what to solve for, enter two values, and click Calculate.

F = m × a

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Summary

Enter any two of force (F), mass (m), or acceleration (a) to instantly solve for the third using Newton’s Second Law: F = m × a.

How it works

Select the unit system: metric (N, kg, m/s\xc2\xb2) or imperial (lbf, lb, ft/s\xc2\xb2).
Choose which quantity to solve for: Force, Mass, or Acceleration.
Enter the two known values in the input fields.
Click Calculate to instantly compute the unknown quantity.
Click Reset to clear all fields and start a new calculation.

Use cases

Physics students verifying homework problems involving F = ma.
Engineers calculating net force required to accelerate a mass.
Robotics designers sizing motors for target acceleration profiles.
Science teachers demonstrating Newton's Second Law interactively.

Frequently Asked Questions

Last updated: 2026-06-09 · Reviewed by Nham Vu