From Physics and Engineering

Stress is a measurable applied force sufficient to distort an object or a system.

Whether measuring the pounds per square inch of pressure that a bolt on a bridge can withstand or the amount of total weight that a bridge can hold altogether as a structure, the kinds of stresses which are being addressed are those external forces which "weigh on" something. If the bolt or the bridge can manage the stress, then there's no problem. Why even mention this here? Because this definition, like others related directly to human stress, is based on the assumption that stress is external -- "out there" somewhere -- and not at issue unless it is applied to us.

 

If the bolt rusts over time, and the bridge is not inspected frequently enough for safety, or a freak ice storm at rush hour overloads the bridge surface with far more weight than anyone ever imagined possible, then stress can become a problem for that bridge -- and for anyone using it.