Simple Science Experiments for a Summer Evening
Jul 14, 2000 (Updated Sep 10, 2000)
At the suggestion of one of my 7-year-old charges, I put together a little science experiment yesterday evening (actually a series of three experiments), and the kids I work with (aged 4- to 7-years of age) loved it, as did their moms, who were enthusiastically called into the room to see what what we had done.
"Density" (mass per unit of volume) is a pretty difficult for kids (and adults?)to understand, as is the notion of what makes things float (if the mass of the floating object is less than the water it displaces). But our experiments helped introduce these concepts, and I think the older ones actually got it!
WHAT YOU NEED:
An ice tray
A small plastic “bottled water” bottle with the top cut off (scissors work)
Plastic food wrap
WHAT WE DID:
I showed my kids a bottled water bottle, with the top 4” cut off, filled with about 5” of water, and a cork. I said I was going to drop the cork into the water and asked if they thought it would float. “That’s easy! It will float!” said one of my precocious 7-year-olds. “Why?” I inquired. “Because it’s light! It’s got lots of holes!” said the same 7-year-old. Not bad, I thought. The 4- and 5-year-olds looked on. I dropped the cork in the water. It floated. “Oooooh!” said the little ones. “See—that was easy!” said the 7-year-old. I took out a penny. “Will this penny float”” I asked. “No, it’s too heavy!” said the other 7-year-old. I dropped the penny in. It sank like a rock. “Oooooh!” said the little ones. “I told you!” said the 7-year-old. End of Experiment 1. I emptied the water bottle to prepare for Experiment 2.
I filled our water bottle with about five” of “hot” tap water and said, “OK kids, I made some dark blue ice cubes earlier today. Do you think ice floats?” “No, it goes in the bottom of the glass!” said a 5-year-old. I twisted the plastic ice tray to liberate the cubes and called the kids up, one at a time, to put an ice cube in the hot water, replenishing the water after every second cube. Of course, the cubes floated.
"Remember the movie, Titanic?" "Yeah, that's the one where the ship runs into the iceberg and then it sinks and the man and the woman are in love and he dies and..." "OK, pretend these ice cubes are little icebergs, except then the water would be cold. Now watch what happens when the blue ice cubes melt!” “Oooooh!” said all the kids at once. As the cubes melted in the hot water, a blue stream shot down toward the bottom of the bottle. For reasons I still don’t completely understand, the melting ice briefly becomes denser than the surrounding water, shooting it down toward the bottom of the container. Use three or four drops of regular food coloring for a striking effect.
Once it neared the bottom, the blue water started to rise again. When my 7-year-olds started asking questions I wasn’t smart enough to answer, I said “I’d better do some more reading,” and moved on to Experiment #3. I like them to know that I have to read to keep “getting smarter” too.
I asked if the kids thought all liquids, like water, juice, pancake syrup, and corn oil, were the same weight, or if some liquids would float on others. Nobody knew.
I had three little cups ready. One contained about 3 oz of pancake syrup, one contained about 3 oz of water colored with blue food coloring (three drops), and one contained about 3 oz of corn oil. “Who wants to be my first helper for this one?” Hands shot up. “Briana, I want you to pour the pancake syrup into the water bottle. Slowly.” She did a good job. “I’ll be my own helper for the water with food coloring (food coloring stains). Let’s see if it floats on the pancake syrup!” “Oooooh!” said the little ones. “I knew it would!” said the 7-year-olds. I let one of the 4-year-olds help pour the corn oil on top of the water. Of course, it floated, and we now had a three-tier liquid layer cake in three colors.
I said, “So pancake syrup is heavy, water is kind of medium, and corn oil is lightest!” I wanted to summarize for those who would want to put what we found into words. I then taped some plastic wrap around the top, so our precious creation wouldn’t spill, and I let each of the kids gently rock it, to see if the liquids would mix. They did not. The coolest part was the way the the corn oil gently rolled on top of the colored water. It looked like a slow motion video of the surface of the ocean on a calm day. I thought of my long-departed Lava Lite.
After a few minutes of oohing and aahing, the kids all wanted to show their moms our three-tiered creation. So I let them rush out to find their moms. They had as much fun as the kids did, rocking our creation, and making comments about oil and water not mixing, and so on. I commented that I hadn’t realized pancake syrup was denser than water.
My two 7-year-olds remembered the word “density” later, and could accurately describe what we had done. The younger ones had a good time and could say we had done a “science experiment.” All asked if we could do more experiments next week. Need I say more?
Note: Two of the above “experiments” came from a science-for-kids type book which I used to have. I’ll have to track it down and review at a later date. Kids do love doing little experiments. The week before, each of us took a tiny magnet and went all around the room, logging (I did the writing) what things magnets are attracted to, and what things they’re not attracted to. Next week, we’re going to see if things really do float more easily in salt water than in fresh water.