Net Force and Equilibrium

In the real world, objects rarely have just one force acting on them. A force is a push or a pull, measured in Newtons (N). When multiple forces act on an object simultaneously, we look at the Net Force ($F_{net}$), which is the vector sum of all individual forces. Think of it like a mathematical 'tug-of-war.' If forces act in the same direction, we add them together. If they act in opposite directions, we treat one direction as positive and the other as negative, then combine them. The direction of the resulting net force determines which way the object will eventually move.

When the sum of all forces acting on an object equals zero ($F_{net} = 0N$), we say the forces are balanced. This state is called mechanical equilibrium. An object in equilibrium experiences no change in its motion. If it was at rest, it stays at rest. If it was moving, it continues moving at a constant speed in a straight line. This is why a book stays on a table: the downward force of gravity is perfectly cancelled out by the upward normal force of the table. Because the forces are equal in size but opposite in direction, the net force is zero.

If the forces do not cancel out ($F_{net} \neq 0$), the forces are unbalanced. Unbalanced forces always cause a change in motion, known as acceleration. This means the object will either speed up, slow down, or change direction. The direction of the acceleration will always be the same as the direction of the net force. For example, if you are riding a bike and the force of your pedaling is greater than the force of air resistance and friction, you will accelerate forward.