Last night I walked into the bathroom in my socks, which promptly became soaked with water. Uh oh. When I turned on the light, I saw that there was a pretty large puddle on the floor next to the pet waterer. The cord that goes to the pump was draped at such an angle that the water had dripped down it to the floor which had amassed the offending pool. Immediately I knew that this was a Teen Bot error, and decided to turn it into a teachable moment. I called Teen Bot to the bathroom and drew his attention to the cord.
“This is why it is important to make sure that the cord doesn’t touch the floor,” I explained. As we spoke, it became clear that he didn’t have an understanding of surface tension. Hoo boy. So, after we took care of the water in the bathroom, I took him back to the kitchen and drew a glass of water, narrating what I was doing along the way. I ground some pepper onto the surface of the water until the surface was well speckled with ground pepper and asked him if he understood what was going on there.
“The pepper is floating because it’s lighter than the water,” he said. As I started shaking my head he corrected himself, “well, I mean it’s less dense than the water.”
“Nope,” I corrected, “the pepper is actually more dense than the water, but it wants to be dry and the water has surface tension that is holding it up. Now, if we take some detergent…” I grabbed the bottle of Dawn and continued, “we can’t feed detergent to the cats, which would simplify the waterer situation, but check this out.” When I dropped a little squeeze of Dawn into the peppered water. The pepper predictably retreated from the drop point and continued to sink to the bottom of the glass.
“Woah,” said Teen Bot.
I smiled at him, “Yes. The detergent breaks the surface tension and the pepper sinks. This is why science is cool and fun. You can learn how the world works in little ways like this. I love that stuff, surface tension, venturi effect…”
Teen Bot stared blankly.
“You don’t know what the venturi effect is?” I asked incredulously. Out came the same glass, rinsed and refilled. I took a drinking straw and cut two small pieces out of it. “Hold this glass for me please.” I held the longer straw segment in the water and positioned the shorter piece at the top of it, pointed at Teen Bot. I blew through the straw and the ensuing spray of water hit his shirt. He laughed hysterically. “Now see,” I said, “when you’re out to pizza with your friends, you can use that trick to spray Coke all over them and make them mad at you. Can you tell me why that works that way?”
“No,” he admitted.
“Bernoulli’s Principle? No? An airplane’s wing is flat on the bottom and rounded on top. The air on top of the wing is moving faster, so it creates a low-pressure zone and the higher pressure air under the wing lifts the plane?”
“Oh right,” Teen Bot said, “I just forgot the name of it.”
I continued, “the venturi effect works pretty much the same way. The air coming out of the straw makes a low pressure zone that sucks the water up the straw and into the airstream.”
“Oooooooohhhhhh,” Teen Bot said, bells ringing.
I know, technically nothing sucks. The low pressure zone simply gives the atmospherically pressurized water somewhere to go. I swear, I knew all of this stuff before high school. What in the world are they teaching kids in school anymore? In all fairness, it was likely taught and he simply wasn’t paying attention. I’m confident that it was memorable enough that he’ll be a little more careful with the pump cord though. And, it was a fun father/son moment as well.