That moment when a science teacher's knowledge of pendulums, momentum, and Newton's laws turns recess into an impromptu physics demonstration! The poor kid on the left is experiencing the practical application of "for every action, there is an equal and opposite reaction"... except there's nothing equal about face-planting into a swing set. Meanwhile, the other children are unwitting participants in a lesson on periodic motion. Playground equipment: where theoretical physics becomes traumatically practical!