What is force in physics?

In physics, force is any interaction that can change an object's motion. It is a vector quantity measured in newtons (N). One newton is the force needed to accelerate a 1 kg mass by 1 m/s².

What are the 3 main types of force this calculator can compute?

This calculator can compute: (1) Net force from mass and acceleration using F = m·a, (2) Weight (gravitational force) using F = m·g, and (3) Friction force using F = μ·N. It also lets you compute centripetal force and pressure from force.

How do I calculate net force?

Net force is calculated using Newton's Second Law: F = m·a, where F is net force in newtons, m is mass, and a is acceleration. If multiple forces act along one line, you can also add them with signs (positive/negative) to get the net force.

How do I calculate weight from mass?

Weight is the gravitational force on an object and is given by F = m·g, where m is mass and g is gravitational acceleration. On Earth, g ≈ 9.81 m/s², so a 70 kg person has a weight of about 687 N.

What units does this force calculator support?

The calculator works natively in SI units (newtons, kilograms, meters, seconds), but it also accepts common alternatives like pounds-force (lbf), grams, metric tons, kilometers per hour squared, and feet per second squared. Results can be shown in both newtons and pounds-force.

Force Calculator – Net Force, Weight, Friction & More

How this force calculator works

This tool is built around Newton’s laws of motion and the standard SI unit of force, the newton (N). It lets you compute several common forces you meet in physics and engineering:

Net force from mass and acceleration: \(F = m \cdot a\)
Weight (gravitational force): \(F = m \cdot g\)
Friction force: \(F = \mu \cdot N\)
Centripetal force in circular motion: \(F = m \cdot \dfrac{v^2}{r}\)
Force from pressure on an area: \(F = p \cdot A\)

1. Net force – Newton’s Second Law

Formula

\[ F = m \cdot a \]

\(F\) – net force (N)
\(m\) – mass (kg)
\(a\) – acceleration (m/s²)

The calculator converts any supported mass and acceleration units to kg and m/s² internally, multiplies them, and then shows the force in newtons and pounds-force.

2. Weight – gravitational force

Formula

\[ W = m \cdot g \]

\(W\) – weight (N)
\(m\) – mass (kg)
\(g\) – gravitational acceleration (m/s²)

On Earth, \(g \approx 9.81\ \text{m/s}^2\). On the Moon, \(g \approx 1.62\ \text{m/s}^2\). The calculator lets you change \(g\) so you can explore weight on other planets.

3. Friction force

Formula

\[ F_\text{friction} = \mu \cdot N \]

\(\mu\) – coefficient of friction (dimensionless)
\(N\) – normal force (N)

The normal force is usually equal to the object’s weight on a horizontal surface, but it can be different on slopes or when additional vertical forces act.

4. Centripetal force in circular motion

Formula

\[ F_c = m \cdot \frac{v^2}{r} \]

\(F_c\) – centripetal force (N)
\(m\) – mass (kg)
\(v\) – speed (m/s)
\(r\) – radius of the circular path (m)

This is the inward force required to keep an object moving in a circle. The faster it moves or the tighter the curve (smaller radius), the larger the required force.

5. Force from pressure

Formula

\[ F = p \cdot A \]

\(p\) – pressure (Pa)
\(A\) – area (m²)

This is useful for hydraulic presses, pistons, and contact forces on surfaces. The calculator converts common pressure and area units to pascals and square meters before multiplying.

Units of force

The SI unit of force is the newton (N):

\[ 1\ \text{N} = 1\ \text{kg} \cdot \text{m/s}^2 \]

Other common units:

Pound-force (lbf) – used in US customary units
kilonewton (kN) – 1 kN = 1000 N, common in engineering

Worked example

A 1,200 kg car accelerates from rest with an acceleration of 3 m/s². What is the net force on the car?

Enter mass = 1200 kg, acceleration = 3 m/s² in the Net force tab.
The calculator uses \(F = m \cdot a\): \(F = 1200 \cdot 3 = 3600\ \text{N}\).
It also shows \(F \approx 809\ \text{lbf}\) and \(3.6\ \text{kN}\).

FAQ

Is force a vector or a scalar?

Force is a vector quantity: it has both magnitude and direction. This calculator focuses on magnitudes, but in real problems you must also consider the direction of each force when finding the net force.

What is the difference between mass and weight?

Mass is the amount of matter in an object (measured in kilograms) and does not depend on location. Weight is the gravitational force on that mass (measured in newtons) and depends on the local gravitational field.