Newton's Second Law Calculator

With the Newton's second law calculator, you can explore the famous second law of motion thanks to Isaac Newton.

Force3 kN1,200 kg × 2.5 m/s²

Force in pounds-force674.4268 lbf

Force in kilograms-force305.9149 kgfthe mass that this force would weigh on Earth

Weight at this gravity11.768 kN1,200 kg × 9.80665 m/s²

Mass1,200 kg2,645.547 lb — mass, not weight

Acceleration2.5 m/s²0.2549 g

Acceleration in g0.2549 gmultiples of standard gravity — what a pilot, a rider or an accelerometer reads

Force as a fraction of weight0.2549×the same as the acceleration in g

Momentum gained per second3,000 kg·m/sforce is the rate of change of momentum, which is Newton's second law in its original form

The formula

F = ma; weight = mg

Mass and weight are different quantities

Mass measures how much matter there is and how strongly it resists acceleration; it is the same everywhere. Weight is the force gravity exerts on that mass, so it changes with location — the same object weighs about a sixth as much on the Moon and nothing at all in free fall, while its mass is unchanged.

The confusion is built into everyday units. A bathroom scale reads in kilograms but measures force, and a "kilogram-force" is the weight of one kilogram under standard gravity — 9.80665 newtons. Pounds are worse, serving as both a mass and a force depending on context, which is why the pound-force has its own name.

Newton originally stated the second law as force being the rate of change of momentum, which is the more general form: it still holds when mass changes, as it does for a rocket burning fuel, where F = ma alone would mislead.