A Newton (N) is the SI unit of force. It is approximately the weight of a small apple (about 100 grams). Everyday forces range from a few Newtons (opening a door) to millions (rocket engines).

What are contact and non-contact forces?

Contact forces require physical touching (friction, tension, normal force, air resistance). Non-contact forces act at a distance (gravity, electromagnetic force, strong and weak nuclear forces).

Can forces cancel each other out?

Yes. When equal and opposite forces act on an object, the net force is zero and the object remains in equilibrium. A book resting on a table has gravity pulling down and the normal force pushing up, canceling perfectly.

Force Calculator

Calculate force using Newton's Second Law — F = m × a

Force Calculator

Calculate force (F = m × a), Newton's second law

Force Calculator

F = m × a

Mass (kg)

Acceleration (m/s²)

Formula

F = m × a

What Is Force?

Force is a push or pull that causes an object to accelerate. Newton's Second Law states that force equals mass times acceleration (F = ma). Force is measured in Newtons (N) in SI units — one Newton is the force needed to accelerate 1 kg at 1 m/s². Understanding force is fundamental to physics, engineering, and everyday life from pushing a shopping cart to launching a rocket.

This calculator solves for any of the three variables: force (F), mass (m), or acceleration (a). Enter two known values to find the third. It also handles weight (gravitational force), friction force, and unit conversions between N, kN, lbf, and kgf — making it useful for both classroom problems and real-world engineering tasks.

How to Use the Force Calculator

Select the variable you want to solve for — force, mass, or acceleration.
Enter the two known values with their units.
Click Calculate.
Read the result with SI and imperial unit equivalents shown below.

Formulas & Unit Conversions

Newton's Second Law:
  F = m × a   (force = mass × acceleration)
  m = F / a   (mass = force / acceleration)
  a = F / m   (acceleration = force / mass)

Weight (gravitational force):
  W = m × g   where g = 9.81 m/s²

Unit conversions:
  1 N = 0.2248 lbf = 0.1020 kgf
  1 lbf = 4.448 N

Net force (multiple forces):
  F_net = F₁ + F₂ + ...  (vector sum)

Weight is a force (measured in Newtons), not mass (measured in kg). A 70 kg person weighs 70 × 9.81 = 686.7 N ≈ 154 lbf on Earth's surface.

Worked Examples

Example 1 — Push a 10 kg Box

A 10 kg box is pushed with an acceleration of 2 m/s². Using F = m × a: F = 10 × 2 = 20 N. That is roughly the force of lifting a 2 kg bag of sugar.

Example 2 — Weight of a 5 kg Object

Weight is gravitational force. For a 5 kg object on Earth: W = m × g = 5 × 9.81 = 49.05 N ≈ 11.02 lbf. This is why mass (kg) and weight (N) are different things.

Example 3 — Net Force with Friction

A 30 N forward push acts on an object with 10 N of friction opposing it. The net force is F_net = 30 − 10 = 20 N in the forward direction. The object accelerates at a = F_net / m.

Frequently Asked Questions

What is the difference between mass and weight?▾

Mass is the amount of matter in an object, measured in kilograms (kg). Weight is the gravitational force acting on that mass, measured in Newtons (N). On Earth, W = m × 9.81. The same object has the same mass on the Moon but a much lower weight because lunar gravity is about 1/6 of Earth's.

What exactly is one Newton?▾

One Newton (1 N) is the force required to accelerate a 1 kg mass at 1 m/s². In everyday terms, one Newton is roughly the weight of a small apple (about 102 grams) held in your hand.

What is net force?▾

Net force is the vector sum of all forces acting on an object. If a 50 N push acts to the right and a 20 N friction force acts to the left, the net force is 30 N to the right. An object accelerates only in the direction of the net force.

How does friction relate to force?▾

Friction is a resistive force that opposes motion. Kinetic friction is calculated as F_friction = μ × N, where μ is the coefficient of friction and N is the normal force (the perpendicular contact force). Higher normal force and higher μ both increase friction.

What are Newton's three laws of motion?▾

First Law (Inertia): An object stays at rest or moves in a straight line at constant speed unless acted on by a net force. Second Law: F = ma — net force equals mass times acceleration. Third Law: For every action there is an equal and opposite reaction (e.g., a rocket expels gas downward, so the gas pushes the rocket upward).