What is Newton's second law?
Newton's second law of motion states that the force acting on an object equals its mass multiplied by its acceleration: F = m × a. Force is measured in newtons (N), mass in kilograms (kg), and acceleration in metres per second squared (m/s²). One newton is the force required to accelerate a one-kilogram mass at one metre per second squared. The law is the cornerstone of classical mechanics and applies to everything from falling apples to orbiting satellites.
How to use this calculator
Choose what you want to solve for—Force, Mass, or Acceleration—using the toggle at the top. Enter the two known values in the input fields and click Calculate. The result appears instantly along with the formula that was applied. When solving for force the card also displays conversions to kilonewtons, dynes, pounds-force, and kilogram-force so you can use the answer in any unit system.
Rearranging the formula
The same equation can be rearranged to solve for any of its three variables. To find mass: m = F / a. To find acceleration: a = F / m. This calculator handles the rearrangement automatically—just pick the unknown and enter the other two values. No algebra required.
Practical applications
Engineers use F = ma to size motors, brakes, and structural supports. Physicists apply it in projectile-motion and orbital-mechanics calculations. Sports scientists analyse the forces generated by athletes during sprinting and jumping. Automotive designers calculate braking distances and crash forces. Even everyday tasks—lifting a bag, pushing a cart—follow Newton's second law, making it one of the most broadly applicable equations in science.
Tips
Always use consistent SI units (kg, m/s², N) to avoid errors. For weight on Earth, use a = 9.81 m/s². Remember that force is a vector—it has both magnitude and direction, though this calculator gives the magnitude. This free tool runs entirely in your browser with no sign-up or download. Bookmark it for quick force, mass, and acceleration calculations on any device.