"Dad, why is there high tide and low tide?"
"The Moon, bud."
"What do you mean? How does the Moon do it?"
"How do you think the Moon does it?"
"Well, I think the Moon gets lonely during the daytime, so it tries to splash us with waves, so that we remember to look up at it."
"I like that."
"Is that what happens?"
"Kinda. The Moon tugs on the water, with gravity, and that causes the tides."
"Like Isaac Newton's apple?"
"You know about that?"
"Yeah, we watched a LiveCast about it in school. The apple fell on his head."
"Right, but do you know what gravity is?"
"Gravity is like... pulling. The Earth pulls everything down towards it. That's why when you throw a rock into the air, it comes back down and plops on the ground. Is that good, Dad?"
"Sure is! But, what about balloons?"
"What about them? Do you have any?"
"Not right now. We're on the beach. So, how come balloons float in the air and fly away into the sky when you let go?"
"Oh, right. Well, not all balloons do that, Dad. Only the ones with helium. The stuff that makes your voice funny. Did you ever try that, Dad?"
"Once or twice. It's bad for you, though, so don't do it."
"But it's funny, though."
"Yeah, I mean, no. Anyway, seems like helium avoids gravity, somehow?"
"I guess. I'll have to ask my teacher about that."
"Good. Let me know what they say."
"I'm surprised you don't know about it, Dad. But what about the tides?"
"What about them?"
"You never explained how the Moon causes the tides."
"Gravity. I already told you."
"No, but like how?"
"Oh, uhh... maybe we can research it together, bud. When we get back to the house. We can look it up together."
"Okay! Can I use your phone for it?"
"Yep. I think it's something with the daily rotation of the earth, but let's make sure, okay?"
"Okay! Hey, Dad?"
"Yes, bud?"
"What causes tide pools?"
"The tides do."
"Well, duh. But is the Moon involved?"
"Yes."
"But, I mean, where do the little fish people riding on seahorses and crabs go when the tide pools disappear?"
"The what?"
"The mermaids. And the fish people. You know... when there's a big tide pool here, you can always see their little coral city underneath the water. They wave at me and I wave back, and I watch their races and teeny battles and sometimes I give them little nibbles of Cheerios from my snackcup."
"What are you talking about, bud?"
"The tide pool cities! C'mon, stop joking, Dad. What happens to all those fish people when high tide comes back? Do they go back to the Moon?"
"I don't know, bud. You'll have to show me next time."
"Okay, Dad. Anyway, can I see your phone now?"
"Yes, bud."