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Force Calculator

Computes net force from mass and acceleration with Newton's second law, reported in newtons, kilonewtons and pounds-force, together with the object's weight under standard gravity.

When to use

You know a mass and its acceleration (or deceleration) and need the net force, or you need an object's weight in newtons or pounds-force from its mass.

Do not use when: You need the gravitational pull between two bodies (use gravitational-force), a spring force (use hookes-law) or the force in circular motion (use centripetal-force).

Formula

force_n = mass_kg × acceleration_m_s2; weight_n = mass_kg × 9.80665; force_lbf = force_n / 4.4482216152605; force_kn = force_n / 1000

Inputs

Parameter	Type	Unit	Required	Description
`mass_kg`	number	kg	yes	Mass of the object in kilograms. Range: > 0
`acceleration_m_s2`	number	m/s²	yes	Acceleration of the mass; negative for deceleration. Use 9.80665 for the force needed to hold the object against gravity.

Outputs

Output	Type	Unit	Description
`force_n`	number	N	Net force F = m·a.
`force_kn`	number	kN	Force in kilonewtons.
`force_lbf`	number	lbf	Force in pounds-force (1 lbf = 4.4482216152605 N).
`weight_n`	number	N	Weight of the mass under standard gravity: m × 9.80665.
`weight_lbf`	number	lbf	Weight in pounds-force.

Example

1200 kg car accelerating at 3 m/s²: {"mass_kg":1200,"acceleration_m_s2":3} → {"force_n":3600,"force_kn":3.6,"force_lbf":809.3122,"weight_n":11767.98}

0.145 kg baseball at 2000 m/s²: {"mass_kg":0.145,"acceleration_m_s2":2000} → {"force_n":290,"weight_n":1.422}

GET https://tttkmbb.com/api/v1/calculate/newtons-second-law?mass_kg=1200&acceleration_m_s2=3

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/newtons-second-law (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/newtons-second-law · Markdown: https://tttkmbb.com/physics/newtons-second-law.md · JSON definition: https://tttkmbb.com/physics/newtons-second-law.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="newtons-second-law"
OpenAPI operationId: calculate_force
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

HyperPhysics – Newton's laws (reference)
NIST CODATA – standard acceleration of gravity g_n = 9.80665 m/s² (standard)
NIST Special Publication 811 – Guide for the Use of the SI, Appendix B (conversion factors) (standard)

FAQ

What is the difference between mass and weight?

Mass (kg) is the amount of matter; weight is the gravitational force on it, W = m·g, measured in newtons. A 1 kg mass weighs 9.80665 N on Earth and about 1.62 N on the Moon.

Is the force the net force?

Yes. F = m·a gives the resultant of all forces; individual forces such as friction or thrust must be combined with vector addition to obtain a.

Related calculators

Acceleration Calculator — Get acceleration from velocities and time first.
Gravitational Force Calculator — Force between two masses by Newton's law of gravitation.
Pressure Calculator — Divide a force by area to get pressure.