Sammy and I were eating applesauce out of those little disposable cups, using regular, stainless steel spoons. When I finished, I set my spoon on my napkin. Sammy said, WHERE'S YOUR SPOON, MOMMY? "It's here on my napkin." YOU PUT IT THERE SO YOUR CUP DOESN'T FALL OVER. "That's right - if I set it in the cup, the cup tips over, like this." I put my spoon in my cup and it tipped over. Sammy knows how this works from her own experiments, but I was impressed that she could identify the reason I set my spoon on the napkin.
After I showed her how it tipped over, I suggested she try her own, which was still about half full. IT DOESN'T TIP OVER, MOMMY! "Do you know why yours stays up and mine tips over?" BECAUSE MINE STILL HAS APPLESAUCE IN IT! "That's right! Because it still has applesauce in it, it is heavier. See, lift them both up." And she picked up the empty and the half-full cups to feel their weight. (I didn't want to teach her about how the weight was distributed, just the simplest, observable facts.)
Then I asked her, "What do you think will happen if I put water in my cup?" I poured some water from her glass into my cup. "Do you think it will stand up?" YES. "Look, you're right. It's heavier with the water in it so it stands up."
Then we had fun pouring water back and forth and testing our theory. I wanted to try just a bit of water and show her that if there was not enough, it would not stand, but there was too much spilling before we got there.
It's not too difficult to find "teaching moments" like this, since a 3-year-old is constantly noticing things, experimenting, and asking WHY? Sammy is finally into the WHY stage in a big way and I'm loving it. This is the part of parenting that I've been looking forward to! I hope I can build a good thread of Teaching Moments here on my blog, because these are true Little Things.