What is the formula for force?

Newton’s Second Law: F = m·a, where F is force in newtons, m is mass in kilograms, and a is acceleration in m/s².

How do I calculate weight on other planets?

Weight is the force due to gravity: W = m·g. Pick a planet; the calculator uses its surface gravity (g) to compute the weight.

What units does the calculator support?

Mass: kg, g, lbm, slug. Acceleration: m/s², ft/s², g (standard gravity). Results appear in newtons (N), kilonewtons (kN), and pound-force (lbf).

What is the difference between lbm and lbf?

lbm is pound-mass (a unit of mass). lbf is pound-force (a unit of force). The calculator converts mass units to SI internally and outputs force in lbf for convenience.

Can acceleration be negative?

Yes. A negative acceleration indicates that the force vector opposes the chosen positive direction. The magnitude is still |F| = m·|a|.

How accurate are the planetary gravities?

Surface gravity values come from NASA fact sheets and are suitable for typical engineering and educational use. Local variations and altitude are not modeled.

Force Calculator | Science

Data Source and Methodology

Authoritative Source: Bureau International des Poids et Mesures (BIPM). “The International System of Units (SI) – 9th Edition (2019).” SI Brochure. Standard gravity g₀ = 9.80665 m/s² aligns with NIST guidance. Planetary surface gravities referenced from NASA Planetary Fact Sheets. Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

Newton’s Second Law:

$$F = m \cdot a$$

Weight (force due to gravity):

$$W = m \cdot g$$

Unit relations:

$$1~\mathrm{N} = 1~\mathrm{kg}\cdot\mathrm{m/s^2}, \quad 1~\mathrm{lbf} = 4.4482216152605~\mathrm{N}$$

Glossary of Variables

m (Mass): Quantity of matter in an object. Inputs accepted in kg, g, lbm, slug.
a (Acceleration): Rate of change of velocity. Accepted in m/s², ft/s², or multiples of g.
g (Gravity): Local gravitational acceleration used in weight calculations. Defaults to 9.80665 m/s² for Earth.
F or W (Force): Result in newtons (N). Also presented as kilonewtons (kN) and pound-force (lbf).
Decimal places: Output display precision; does not affect internal calculation accuracy.

How It Works: A Step-by-Step Example

Suppose a 75 kg athlete accelerates at 2.5 m/s². Using Newton’s Second Law:

$$F = m \cdot a = 75~\mathrm{kg} \times 2.5~\mathrm{m/s^2} = 187.5~\mathrm{N}$$

Convert to other units:

$$kN = \frac{187.5}{1000} = 0.1875~\mathrm{kN}, \quad lbf = \frac{187.5}{4.4482216152605} \approx 42.15~\mathrm{lbf}$$

Frequently Asked Questions (FAQ)

What is the difference between mass and weight?

Mass is an intrinsic property of matter measured in kilograms; weight is the force due to gravity acting on that mass, measured in newtons or pound-force.

Can I enter negative acceleration?

Yes. Negative acceleration yields a negative force if mass is positive, indicating a direction opposite to the chosen positive axis.

Which gravity value does “g” use?

The calculator uses the standard gravity g₀ = 9.80665 m/s² for the “g” unit and for Earth, per BIPM/NIST convention.

How are unit conversions handled?

All inputs are converted to SI internally: kg for mass and m/s² for acceleration. Results are computed in newtons and displayed additionally in kN and lbf.

Why is my result slightly different from another website?

Minor differences arise from rounding, use of slightly different constants, or number of displayed decimals. This tool uses high-precision constants and rounds only for display.

Do you support slugs and pound-mass?

Yes. 1 slug = 14.5939029372 kg; 1 lbm = 0.45359237 kg. The calculator converts these to SI before computing force.

Tool developed by Ugo Candido. Content verified by CalcDomain Editorial Team.
Last reviewed for accuracy on: September 15, 2025.