Force equilibrium is a fundamental concept in physics. When an object is in equilibrium, the sum of all forces acting on it equals zero. Here we see a block resting on a surface. The weight force pulls downward, while the normal force from the surface pushes upward with equal magnitude, resulting in zero net force.
When an object hangs from a string, it demonstrates another example of force equilibrium. The tension force in the string pulls upward on the mass, while gravity pulls downward. For the object to remain stationary, these forces must be equal in magnitude but opposite in direction.
In more complex situations, multiple forces can act on an object simultaneously. For equilibrium to exist, we must consider all forces acting in different directions. The sum of forces in the x-direction must equal zero, and the sum of forces in the y-direction must also equal zero.
To better understand equilibrium, let's compare balanced and unbalanced forces. In the top example, unbalanced forces result in a net force that causes acceleration. In the bottom example, balanced forces result in zero net force, meaning no acceleration occurs and the object maintains its current state of motion.
Force equilibrium is directly related to Newton's First Law of Motion. This law states that objects maintain their state of motion unless acted upon by unbalanced forces. Whether an object is at rest or moving at constant velocity, equilibrium means the net force is zero, confirming Newton's fundamental principle of inertia.