Question

The mayor of a city reprimands some city employees because they will not remove the obvious sags from the cables that support the city traffic lights. What explanation can the employees give? How do you think the case will be settled in mediation?

Short answer

The employees would win the case against the city mayor because physics tells s that cables must always sag in order to support their own weight.

Step-by-step solution

A concept:

Force is the force exerted by a rope, string, cable or similar object on one or more objects. Anything pulled, suspended, supported, or swung from a rope, string, cable, etc. is subject to a tensile force. Like all forces, tension can accelerate objects or cause them to deform.

The explanation is given by employees:

Consider a cable between two poles. The cable is in equilibrium, meaning that neither end of the cable is moving faster than the other. Let’s divide the cable into little segments which have a certain mass m. Again, in order for the cable to be in equilibrium, every segment needs to be in equilibrium, and the net force on the segments has to be zero.

As known, gravity is acting on our segment of mass m, so you need another force or forces to balance gravity out.

Since gravity acts vertically downwards in this case, you need a vertical component of the tension in the cable left and right.

If the cable was perfectly horizontal then you wouldn’t have had the forces to balance gravity out.