Newtons Second Law
Calculator

It states that the net force acting on an object equals its mass times its acceleration, meaning force is what causes a change in velocity, not what maintains a constant velocity. Given any two of force, mass, or acceleration, the calculator solves for the third.

Acceleration is inversely proportional to mass for a fixed force, so a heavier object accelerates less than a lighter one under the identical applied force. This is why pushing an empty shopping cart speeds it up far more easily than pushing one loaded with groceries.

No — mass (in kilograms) is the amount of matter in an object and stays constant everywhere, while weight is the force of gravity on that mass (weight = mass × gravitational acceleration) and changes depending on location, such as being lower on the Moon. This calculator's mass input should always be in kilograms, not a weight in pounds or newtons.

Net force is the vector sum of every force acting on an object — including friction, gravity, applied pushes, and air resistance — after they've been added or subtracted based on direction, not just one force in isolation. If opposing forces are balanced, net force is zero and the object doesn't accelerate at all, regardless of how large the individual forces are.

Yes — a negative result simply means the acceleration points in the opposite direction to the one you defined as positive, which typically represents deceleration (slowing down) if the object was already moving in the positive direction. The sign convention is a bookkeeping choice, not an indication that something unusual is happening physically.