Newton's Second Law

Newton's second law F = m · a: find force, mass or acceleration with unit conversion and a step-by-step solution.

What to find:

Numbers can be decimals (2.5), fractions (1/3) or scientific notation (1.5e3). Pick any units — the calculator converts them to SI.

Test yourself

The Newton's second law calculator finds force, mass or acceleration from the other two. You can enter grams and tonnes, kilonewtons and cm/s² — the solution shows the conversion to SI, the formula and the substitution.

Newton's laws

First law: a body stays at rest or moves uniformly in a straight line unless acted on by an unbalanced force.
Second law: the acceleration of a body is directly proportional to the net force and inversely proportional to its mass.
Third law: two bodies act on each other with forces equal in magnitude and opposite in direction.

F = m · a, m = F / a, a = F / m

The unit of force is the newton: 1 N = 1 kg · m/s², the force that gives a 1 kg mass an acceleration of 1 m/s². Force and acceleration may be negative, meaning they point against the chosen axis (for example, when braking).

Example 1. A 1200 kg car accelerates at 2.5 m/s²: F = 1200 · 2.5 = 3000 N = 3 kN.

Example 2. A 500 N force acts on a 50 kg body: a = 500 / 50 = 10 m/s².