Physics calculator
Force Calculator
Calculate force, mass, or acceleration using Newton's second law.
Calculated force
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Enter two compatible values to calculate.
What is force?
Force is a push or pull that can change an object's motion. The SI unit of force is the newton (N). This calculator finds force, mass, or acceleration when the other two values are known.
Newton's second law
Newton's second law says that an object's net force equals its mass multiplied by its acceleration:
Force and mass are converted to newtons and kilograms, while acceleration is converted to meters per second squared before calculation.
Force, mass, and acceleration
Force is measured in newtons, mass in kilograms, and acceleration in meters per second squared. Rearranging the equation gives:
A negative acceleration represents acceleration in the opposite direction of the chosen positive direction. Mass cannot be negative.
Worked examples
For a 10 kg object accelerating at 2 m/s²:
For 20 N of force acting on 4 kg:
One kilogram accelerating at standard gravity produces:
Units and conversions
The calculator uses SI units internally. It uses 1 lb = 0.45359237 kg, 1 ft/s² = 0.3048 m/s², standard gravity g = 9.80665 m/s², and 1 lbf = 4.4482216152605 N. A newton and a pound-force are both force units, but they are not numerically equal.
Common uses
Force calculations are useful in mechanics, engineering, vehicle dynamics, structural analysis, sports science, and estimating the load produced when an object accelerates or decelerates.
Frequently asked questions
What is the difference between newtons and pounds-force?
A newton is the SI unit of force. A pound-force is an imperial force unit; 1 lbf equals approximately 4.44822 N.
Can acceleration be negative?
Yes. Negative acceleration indicates a direction opposite to the selected positive direction, so the resulting force can also be negative.
Can mass be zero or negative?
Zero mass can produce zero force, but it cannot be used as a divisor when finding acceleration. Negative mass is rejected because it is not a valid ordinary physical input.
Why is no result shown?
The calculator needs two valid known values. Blank, non-finite, negative-mass, or division-by-zero inputs are not used.
What does standard gravity mean?
Standard gravity is the defined reference acceleration 9.80665 m/s², written as g or g0. It is a reference value, not a promise that gravity is identical everywhere.