We explored another one of water's properties: surface tension. First, we filled up a cup and observed how the top became a dome. The kids were amazed to see the water staying in the cup. You can actually see their heads as they were flat on the floor for a better look.
I gave each one a shiny penny, a dropper, and a cup of water. I asked how many drops of water they though could fit on the penny. Big Sister said 5, Little Guy said 1. After working hard squishing drops, they found out that it took 17 drops or more for the water to spill!
They were able to see a perfect little dome on top of the penny.
Then, we experimented with a few water solutions. Big Sister added coarse salt to a cup of water. We wanted to observed if salty water had an effect on the water surface tension. We were surprised to see none or very little changes. We were able to continue to create domes with about 15 drops in each coin.
Here is Little Guy building his salty water dome.
Our next solution included water and liquid detergent. I asked the kids to make a fresh water dome, and add just one drop of the soapy water. The soap weakened the surface tension and the water spilled immediately.