About Newton's Second Law
Newton's Second Law of Motion is one of the foundational relationships in classical mechanics: the net force acting on an object equals the object's mass multiplied by its acceleration, written as F = m × a. It quantifies exactly how much force is needed to change an object's motion — the more massive the object, or the faster you want it to speed up, slow down, or change direction, the more net force is required. This calculator lets you solve the equation for any one of the three quantities (force, mass, or acceleration) when the other two are known, and converts between common metric and imperial units automatically.
Understanding the formula
F = m × a holds whenever mass is constant and speeds are far below the speed of light (the everyday regime of cars, sports, machinery, and lab experiments). In SI units, mass is measured in kilograms (kg), acceleration in meters per second squared (m/s²), and force in newtons (N), where 1 N = 1 kg·m/s² by definition. Rearranged, the same equation gives mass as m = F ÷ a, and acceleration as a = F ÷ m. The direction of the acceleration always matches the direction of the net force — if you push an object to the right, it accelerates to the right, regardless of which way it was already moving.
Net force, not just one force
The "F" in F = m × a is the net force — the vector sum of every force acting on the object (applied force, friction, gravity, air resistance, normal force, etc.), not any single force in isolation. If several forces act on an object at once, add them (accounting for direction) before applying the formula. An object with zero net force has zero acceleration and moves at constant velocity (or stays at rest) — this is Newton's First Law, and it's the special case of the Second Law where a = 0.