Particle Equilibrium Recall that a particle in equilibrium is one for which the external forces are balanced. Static equilibrium involves objects at rest, and dynamic equilibrium involves objects in motion without acceleration. We now make use of our knowledge of the different types of forces and use free-body diagrams to solve additional problems in particle equilibrium. Different Tensions at Different Angles Consider the traffic light (mass of 15.0 kg) suspended from two wires as shown below. Find the tension in each wire, neglecting the masses of the wires. Sketch (a) ?1y 30° Just some of the forces are shown here. Only forces on the system are shown. ?, ?, ?, T2 30 145° O ?, y ?2 30° 45° × ?2 13 13 System of interest (b) (c) Free-body diagram TZV ?, T2 45º TIY T2x ?1x . 13 The net vertical force is zero, so ?1y+ ?zy = - ? T2x The net horizontal force is zero, so ?„x =- ?2x (d) (e) A traffic light is suspended from two wires. (b) Some of the forces involved. (c) Only forces acting on the system are shown here. The free-body diagram for the traffic light is also shown. (d) The forces projected onto vertical (y) and horizontal (x) axes. The horizontal components of the tensions must cancel, and the sum of the vertical components of the tensions must equal the weight of the traffic light. (e) The free-body diagram shows the vertical and horizontal forces acting on the traffic light.