Force Calculator

Calculate force, weight, friction, gravitational attraction and pressure with step-by-step workings

Newton's Second Law

// Newton's Laws of Motion

1st Law (Inertia)ΣF = 0 → constant velocity
2nd Law (F = ma)F = m × a
3rd LawEvery action has equal & opposite reaction
WeightW = m × g  (g = 9.81 m/s² on Earth)
Frictionf = μ × N  (μ = coefficient, N = normal force)
PressureP = F / A  (Pa = N/m²)

Newton's Laws and Force

Force is a push or pull that causes an object to accelerate, decelerate or change direction. It is measured in Newtons (N), where 1 N is the force needed to accelerate 1 kg at 1 m/s².

Formulas

Weight vs Mass

Mass is the amount of matter in an object (kg) — it is constant everywhere. Weight is the gravitational force acting on that mass (N) — it varies with location. A 70 kg person weighs 686 N on Earth but only 113 N on the Moon.

Note: All calculations assume classical (Newtonian) mechanics. These formulas break down at velocities approaching the speed of light or at quantum scales.
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Newton's Three Laws of Motion
Inertia, F=ma, and action-reaction explained with everyday examples.
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// Weight ≠ Mass

Mass is measured in kg; weight is a force in Newtons. 70 kg on Earth weighs 686 N. The same mass on the Moon weighs only 113 N.

// Friction Basics

Static friction (preventing motion) is slightly higher than kinetic friction (resisting ongoing motion). This is why it's harder to start sliding than to keep sliding.

// Pressure Example

A stiletto heel (1 cm² area) at 60 kg exerts: P = 588 N / 0.0001 m² = 5.88 MPa — greater than a car tyre pressure by 100×.

// g Varies

g is not exactly 9.81 everywhere. It's ~9.78 at the equator (centrifugal effect) and ~9.83 at the poles. Altitude also reduces g slightly.