In 1978, in an accident at a school in Harrisburg, Pennsylvania, several children lost parts of their fingers when a nylon rope suddenly snapped during a giant tug-of-war among 2300 children. The rope was known to have a breaking tension of 58,000 N. Each child can exert a pull of approximately 130 N. Was it safe to employ this rope in this tug-of-war?

We assume that one-half of the children are pulling from each end during the tug-of-war. If each child exerts a force of 130 N toward their end of the rope, the middle section of the rope is subject to a net force of zero. This is because there are equal and opposite forces applied from each end; and the middle section therefore will not accelerate toward either end.

But, the parting tension being applied to the rope is not zero! Its magnitude is given by the size of the applied forces, namely

This is much greater than the rated breaking tension of 58,000 N, so this rope was not safe to use!