What is force?

Force is a push or a pull that one object applies to another. Several usually act on the same thing at once. They point in different directions and offset each other, sometimes completely. Whatever is left over is called the net force. Only that leftover changes anything, which is why a thing can have plenty of force on it and still not move.

Force is a push or a pull that one object applies to another. Your hand does it, gravity does it, so does the road under a tyre. Forces rarely act alone, and direction decides what happens when they meet: two pushing opposite ways subtract from each other, two pushing the same way add up. Whatever is left over is the net force. That leftover is the only part that moves anything. A book on a table has gravity pulling it down and the table pushing back just as hard, so nothing is left over and the book sits still. Newton's second law puts numbers on it: acceleration is net force divided by mass. So one push sends an office chair rolling and barely shifts a filing cabinet, because the leftover is the same and the mass is not.

Force works like two people pushing a stalled car. Push from the same end and their efforts add up, so the car moves off faster than either of them could manage alone. Put one at the front instead and the efforts subtract, so the car sits there while both of them strain. The car responds only to what is left once the two pushes are added together.