"A particle is in equilibrium provided it is at rest if originally at rest or has a constant velocity if originally in motion. Most often, however, the term "equilibrium" or, more specifically, "static equilibrium" is used to describe an object at rest. To maintain equilibrium, it is necessary to satisfy Newton's first law of motion, which requires the resultant force acting on a particle to be equal to zero." p81

ELASTIC SPRING

EQUILIBRIUM
A STEADY-STATE CONDITION IN WHICH FORCES, TORQUES, FLOWS MAY BE HAPPENING BUT THE SYSTEM UNDER STUDY IS NOT CHANGING WITH TIME.

EQUILIBRIUM
A STATE OF BALANCE. FORCES, MOMENTS, FLOWS MAY BE OCCURRING IN A SYSTEM BUT NO NET CHANGE IS OCCURRING IN THE SYSTEM.

FREE-BODY DIAGRAM
A DRAWING OF THE OBJECT UNDER STUDY, SHOWING ONLY THE OBJECT AND ALL FORCES APPLIED TO THE OBJECT.

LINEAR
PROPERTY OF SYSTEMS WHERE THE SYSTEM OUTPUT OR RESPONSE IS IN DIRECT PROPORTION TO THE INPUT. DOUBLING THE INPUT (LOAD, FORCE, ENERGY, TENSION,...) HAS THE EFFECT OF DOUBLING THE OUTPUT (STRETCH, COMPRESSION, DISPLACEMENT,...)

LINEAR ELASTIC SPRING

PULLEY
A WHEEL WITH A GROOVE, ON AN AXLE THAT CARRIES A BELT, ROPE OR WIRE THAT CAN BE USED TO PULL, LIFT OR OTHERWISE MOVE OBJECTS