Okay so the subtitle is a bit of a joke, but I really do believe that kids should be immersed in science. They should not just learn from a textbook (although some great learning can come from books). They need to feel, see, hear, and sometimes smell and taste science.
I did this activity years ago when our oldest was just 4 or 5. I wanted to run it again for the young ones, but I added some ideas to it so that the older ones would learn too. (though honestly they would have had fun doing the original version again).
Fill a 5 gallon bucket (or other large container) with water. Collect a few items that can be dropped in and ask the kids if it will sink or float.
Let the kids hold the objects, so that they can make their guess.
Then let them run around the house and find things that they want to try (this is a good time to make sure that your cell phone is out of reach). This is an important part of the activity. You pick some objects to get them started, but they need to be able to pick their own items to test the different theories that they have.
Do not tell them anything. Just let them guess and try dropping them in. Eventually they will start to figure out why some things sink and some float.
Once they figure it out, you can explain the word “density”. A simple definition might be “how heavy something is compared to how big it is”.
Sometimes funny things will happen like a pen we dropped in sank, but only 1 end touched the bottom. Or some objects might float for a little while and then sink when a air bubble escapes. These “funny” things open the door for some good conversations.
This time we had a hair-tie that did not sink, but technically was not floating.
If you look closely you can see light shining around the hair-tie. This is because the water is bent and reflecting the light. The hair-tie was denser than water, which we saw later when it sank, but was light enough that it did not break the surface tension of the water.
Water molecules act like tiny magnets. When an object goes into water, it must break those magnets apart. The magnetic forces are very weak , so it is not normally a problem, but if an object is light enough, it can stay on top. A water strider is a great example of this. Unfortunately it is not warm enough to find some and take a picture, but you can see a good on here.
For the older kids:
I dropped a plastic container in. Of course it floated. Then we carefully added pennies until it sank.
Then we used a kitchen scale to weight the container and pennies, after we dried them.Finally I took the pennies out and filled the container with water. I asked the kids if it would weigh more or less than the container with the pennies.
The result: they weigh the same! Well, not quite, but then Elijah looked closely and declared, “It is surface tension!” Nice save, Elijah. We had actually poured in a little too much water and it was above the top of the container. When the surface tension allows the water to go above the top, it is called a meniscus.
When we added the pennies, we increased the density of the container until it was as dense as the water at which point it sank. (make sure you container does not have a lip that will trap air in it).
This is also a good time to explain “specific gravity”, which is the ratio of an objects density to the density of water. Water has a specific gravity of 1 (because that would be comparing water to itself). If the specific gravity is greater than 1, it will sink. If it is less than 1, it will float.
When you do a science activity with your kids, don’t be too structured. Sometimes you need some structure to keep them safe, but try to let them play with the science. Let them get their hand on it and explore. Even if you think their idea is silly, they will learn from it, and occasionally I do too.
There’s a great sink and float puzzle also available.