Me, talking to my gang of teenage kids about their day. I asked my oldest son what he was working for the upcoming science olympiad. My son: "We're working on a pendulum." Me: "Must be a lot of back and forth." ACTUAL LAUGHTER! After we settled back down, my son said, "We're also working on objects." I said "Objects?" puzzled. "No Dad! Optics!" "Oh! Optics.....I see. (big grin)" Laughter again! TRIUMPH!
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.