**Static Equilibrium for a Particle**

**A particle: **An object with inertia
(mass) but of negligible dimensions

**Equilibrium equations for a particle:**
A particle is in equilibrium if the resultant of ALL
forces acting on the particle is equal to zero

**Equilibrium equations in component form:**
In a rectangular coordinate system the equilibrium equations can be represented
by three scalar equations:

**Free-Body diagram: **A diagram
showing the particle under consideration and all the forces acting on this
particle. Each force in this diagram must labeled.

**String or cable: **A mechanical
device that can only transmit a tensile force along itself.

**Linear spring: **A mechanical device
which exerts a force along its line of action and proportional to its
extension.

**Frictionless pulleys:** For a
frictionless pulley in static equilibrium, the tension in the cable is the same
on both sides of the pulley.

**Examples:**