- Equilibrium and Statics
- 12.1: Conditions for Static Equilibrium
- The First Condition for Equilibrium
Equilibrium and Statics
When all the forces that act upon an object are balanced, then the object is said to be in a state of equilibrium. The forces are considered to be balanced if the.what online
Equilibrium , in physics , the condition of a system when neither its state of motion nor its internal energy state tends to change with time. A simple mechanical body is said to be in equilibrium if it experiences neither linear acceleration nor angular acceleration; unless it is disturbed by an outside force, it will continue in that condition indefinitely. For a single particle, equilibrium arises if the vector sum of all forces acting upon the particle is zero. A rigid body by definition distinguished from a particle in having the property of extension is considered to be in equilibrium if, in addition to the states listed for the particle above, the vector sum of all torques acting on the body equals zero so that its state of rotational motion remains constant. An equilibrium is said to be stable if small, externally induced displacements from that state produce forces that tend to oppose the displacement and return the body or particle to the equilibrium state. Examples include a weight suspended by a spring or a brick lying on a level surface. An equilibrium is unstable if the least departure produces forces that tend to increase the displacement.
We say that a rigid body is in equilibrium when both its linear and angular acceleration are zero relative to an inertial frame of reference. This means that a body in equilibrium can be moving, but if so, its linear and angular velocities must be constant. We say that a rigid body is in static equilibrium when it is at rest in our selected frame of reference. Notice that the distinction between the state of rest and a state of uniform motion is artificial—that is, an object may be at rest in our selected frame of reference, yet to an observer moving at constant velocity relative to our frame, the same object appears to be in uniform motion with constant velocity. Because the motion is relative , what is in static equilibrium to us is in dynamic equilibrium to the moving observer, and vice versa. Since the laws of physics are identical for all inertial reference frames, in an inertial frame of reference, there is no distinction between static equilibrium and equilibrium. In equilibrium, the linear acceleration is zero.
For an object to be in equilibrium, it must be experiencing no acceleration. This means that both the net force and the net torque on the object must be zero. Here we will discuss the first condition, that of zero net force. In order to achieve this conditon, the forces acting along each axis of motion must sum to zero. For example, the net external forces along the typical x — and y -axes are zero.
If an object is at equilibrium, then the forces are balanced. Balanced is the key word that is used to describe equilibrium situations. This extends from Newton's first law of motion. An object at equilibrium is either This too extends from Newton's first law of motion.
12.1: Conditions for Static Equilibrium
The First Condition for Equilibrium