Pendulum (mechanics) Puns

Now, I am not a dad, but I told my father this joke and he giggled, so I feel like it still counts as a dad joke. In a unit on wave mechanics, my class was discussing pendulums. As we talked about pendulums and how they related to wave mechanics, my buddy said, in a contemplative manner, "I just don't know what to think about pendulums." I responded, "So you could say, your thoughts have gone back and forth on the matter." Many groans were had.