Force Calculator

Quick Answer

A 10 kg object accelerating at 9.8 m/s^2 experiences a net force of 98.00 N. The weight of a 75 kg person on Earth is 735.75 N.

Newton's Second Law (F = ma)

Solve For

Mass (kg)

Acceleration (m/s²)

Weight from Mass (W = mg)

Mass (kg)

Gravitational Acceleration (m/s²)

Earth: 9.81, Moon: 1.62, Mars: 3.72, Jupiter: 24.79

Common Examples

Input	Result
m = 10 kg, a = 9.8 m/s^2	F = 98.00 N
F = 500 N, m = 50 kg	a = 10.00 m/s^2
F = 200 N, a = 4 m/s^2	m = 50.00 kg
m = 75 kg, g = 9.81 m/s^2 (weight)	W = 735.75 N
m = 75 kg, g = 1.62 m/s^2 (Moon)	W = 121.50 N

How It Works

This calculator uses Newton’s Second Law of Motion:

F = m x a

Where:

F = net force in Newtons (N)
m = mass in kilograms (kg)
a = acceleration in meters per second squared (m/s^2)

One Newton is defined as the force required to accelerate a one-kilogram mass at one meter per second squared. The equation can be rearranged:

Force: F = m x a
Mass: m = F / a
Acceleration: a = F / m

Weight as a Force

Weight is the gravitational force acting on an object:

W = m x g

Where g is the gravitational acceleration. On Earth’s surface, g = 9.81 m/s^2. Weight is measured in Newtons, not kilograms. A 1 kg mass weighs 9.81 N on Earth but only 1.62 N on the Moon, because the Moon’s gravitational acceleration is smaller.

Force Units

1 Newton (N) = 1 kg x m/s^2
1 kilonewton (kN) = 1,000 N
1 pound-force (lbf) = 4.44822 N
1 dyne = 0.00001 N

Net Force and Multiple Forces

Newton’s second law applies to the net (total) force on an object. If multiple forces act on an object, the acceleration depends on the vector sum of all forces. This calculator assumes you are entering the net force or solving for it directly.

Worked Example

A 1,200 kg car accelerates at 2.5 m/s^2. The net force is F = 1,200 x 2.5 = 3,000 N (3 kN). Conversely, if a 50 N force acts on a 10 kg box, the acceleration is a = 50 / 10 = 5.0 m/s^2. For weight: a 75 kg person on Earth weighs W = 75 x 9.81 = 735.75 N. On Mars (g = 3.72 m/s^2), the same person weighs W = 75 x 3.72 = 279.00 N.

Related Calculators

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Calculate kinetic energy, mass, or velocity using the formula KE = ½mv².

Frequently Asked Questions

What is a Newton?

A Newton (N) is the SI unit of force. It is defined as the force needed to accelerate a 1 kilogram mass at 1 meter per second squared. One Newton is approximately the weight of a small apple (about 100 grams) on Earth. The unit is named after Sir Isaac Newton.

What is the difference between mass and weight?

Mass is a measure of how much matter an object contains, measured in kilograms. It does not change based on location. Weight is the gravitational force acting on that mass, measured in Newtons. Weight changes depending on the gravitational field. A 70 kg person has the same mass everywhere but weighs 686.7 N on Earth and only 113.4 N on the Moon.

Does F = ma work for objects at rest?

Yes. If the net force on an object is zero, then acceleration is also zero, and the object remains at rest or continues moving at constant velocity. This is consistent with Newton's first law (the law of inertia). F = ma applies to all scenarios, including equilibrium.

What gravitational acceleration values are common?

Earth surface: 9.81 m/s^2. Moon: 1.62 m/s^2. Mars: 3.72 m/s^2. Jupiter: 24.79 m/s^2. Venus: 8.87 m/s^2. The Sun: 274 m/s^2. These values are averages at the surface level.

Can force be negative?

Yes. A negative force indicates force in the opposite direction of the chosen positive axis. For example, friction force is typically negative relative to the direction of motion. The calculator works with negative values for force and acceleration.