Ever gotten unsteady on your feet or had your equilibrium messed up so you felt dizzy? In this sense, your balance has been compromised and there is usually something going on in your ears or with your brain to make it happen. While this use of the word equilibrium is a little different than the way it is used in physics, it is related. This comparison might help you remember what the physics definition of equilibrium means. In biology, the term means a state of physical balance, in physics it means a state in which all the physical forces acting on an object are balanced. In other words, an object is in equilibrium if every force is cancelled out by a second force.
Question
Is this object in equilibrium? How do you know?
Yes, this object is in equilibrium. Despite the fact that the 5 N does not equal the 15 N force, each force has another that "cancels" it out. The net force on this object is zero.
Question
Is this object in equilibrium? How do you know?
No, because the forces in the x-direction does not equal one another. The net force on this object is 10 N to the right.
Because of Newton's First Law, we can confidently state that an object in equilibrium will have no acceleration. It must be either not moving or moving at a constant speed. This becomes an essential understanding as we move on to discuss weight and apparent weight in this lesson.
