Transform water play into an incredible science lesson with these simple supplies: a cup and a plastic lid, a jar and a piece of screen. The first time I shared these two investigations with my kids, they were simply spellbound. The results are so surprising, they seem like magic.

But it’s not magic–it’s science! Here’s how to do it:

Gravity-defying Lid

Show your child that if you put a plastic lid on top of a dry cup and turn them upside down, the lid falls as soon as you remove your hand. Now put the lid on a cup that has water in it. Turn them upside down (using two hands to keep the lid in place) and when you let go, the lid sticks! You can even shake it, and the lid still stays in place, keeping all of that water inside the cup. Try it with the cup almost empty or completely full of water. Try two cups on the same lid and see if you can get them both to suction on. 

Magic Screen

Secure a nylon stocking or piece of netting over a cup with a rubber band, or use a mason jar and metal ring. Make sure the screen is smooth and flat. Show your child how water can flow into the container easily, passing right through the screen. Then place a plastic lid on top and turn the jar or cup upside down. Take away the lid, and the water stays in the jar! And it will stay in as long as the jar is level and the screen is flat. But if you tip it just a little, then all the water rushes out. Poke the screen, some water dribbles out. Notice how each time water goes out, air bubbles rush up?

The short answer for why these activities work is that physics is awesome, and water is amazing. Forces need to be balanced. If the water is going to come out of the cup, something needs to take its place. For more detailed explanations, you can check out a YouTube video I put together or this free foldable booklet that can be downloaded here.

Oh, and a quick pro tip: the Magic Screen activity works best with water that has strong surface tension and is not soapy. So if you do these activities during bathtime, see if you notice a difference in how it works before and after you add the bubbles.


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