Explanation and example

Along a selected axis, Newton’s second law is F = ma. Leave the unknown field blank and enter the other two in newtons, kilograms or m/s². The signs of force and acceleration indicate direction relative to the axis; mass must remain positive.

Example: a net force of 6 N on a mass of 2 kg creates an acceleration of 3 m/s². Multiplying 2 by 3 checks the result. A force of −6 N on the same mass produces −3 m/s².

Limits

F means the sum of external forces. Entering only one force while ignoring friction or another force will not give the full motion. Zero force and zero acceleration cannot determine mass uniquely.