A variant of the experiment we just did was performed by Galileo long before the concept of energy was known. The question we ask is how does the pendulum respond if I prevent it from following the ``conventional'' path by introducing a pin in the path of the string holding the pendulum such that it ``trips'' the pendulum as it passes the vetical position. We observe that at least if we leave enough string between the pin and the pendulum mass the mass although awkwardly does swing to that same max height position that corresponds to how much mechanical energy was introduced into the system from the outset. If I tease the system even more by leaving too little string to allow the mass to reach the top then kinetic energy remains at the max height allowable and more complicated forms of motion occur. Typically such motion eventually results in dissipation associated with the tension in the string which ends up acting along the direction of propagation.