Force Calculator

Newton's Second Law — F = ma — is one of the most useful equations in physics. It tells you that the net force on an object equals its mass times the acceleration that force produces. Rearranging it lets you solve for any of the three quantities when the other two are known, which is exactly what this calculator does.

Force is measured in Newtons (N), where 1 N = 1 kg·m/s² — the force needed to accelerate a 1 kg mass at 1 m/s². Mass is in kilograms and acceleration in meters per second squared. Because force is a vector, the answer also has a direction: positive values point along the direction of acceleration, negative values point opposite.

A delivery worker pushes a 25 kg box across a smooth floor with a horizontal force. The box accelerates at 1.6 m/s². How much force is being applied?

• Mass: m = 25 kg
• Acceleration: a = 1.6 m/s²
• Force: F = m × a = 25 × 1.6 = 40 N

A second example: a 1,500 kg car accelerates from 0 to 27 m/s (about 60 mph) in 7 seconds. Average acceleration is 27 ÷ 7 ≈ 3.86 m/s², so the average net force from the wheels on the road is 1,500 × 3.86 ≈ 5,786 N.

• Physics homework — solving F = ma problems with mass, acceleration, or force unknown.
• Engineering estimates — sizing motors, springs, or actuators for a target acceleration on a known load.
• Vehicle dynamics — quickly checking required thrust or braking force for a given mass and acceleration.
• Lab work — confirming experimental data matches the F = ma prediction within measurement error.
• Free-fall and gravity problems — using F = mg to find weight from mass on Earth or other planets.

• Confusing weight with mass. Always enter mass in kilograms here, not weight in Newtons or pounds.
• Using gravitational acceleration where you shouldn't. g = 9.8 m/s² applies to free fall on Earth — not to a box being pushed across a floor.
• Ignoring opposing forces. If friction or air resistance acts on the object, the F you compute from F = ma is the net force, not the applied force.
• Mixing unit systems. Mass in pounds with acceleration in m/s² gives nonsense. Convert pounds to kilograms (× 0.4536) first.
• Forgetting that acceleration is a vector. A car going around a curve at constant speed is still accelerating — and therefore experiencing a net force toward the center of the curve.