Exploring Surface Tension: Doing Fun Science at Home during School Closures (Activity #18)

By Sandra Slutz on April 27, 2020 11:00 AM

Follow along with a Science Buddies parent who is using family STEM activities to keep her kids learning at home during the COVID-19 school shutdown. New posts every Monday, Wednesday, and Friday. Today's adventure... exploring surface tension by making wire water striders.

Student touching a wire water strider floating in a plate of colored water

A Spill Leads to Exploring Surface Tension

What happens when you put a freshly laundered tablecloth on the table? Well, in my house, it immediately triples the chance that someone will spill something at the next meal. Okay, that's probably not true, and if I bothered to keep track of the "data," I'd likely be shown to be wrong — but it sure feels like that's how it goes! Today's spill was just water, and the cool thing was that this tablecloth (a relatively new one for us) is fairly water repellent. So, the spilled water formed several dime-sized blobs. My second-grader was fascinated. She'd never taken the time to really look at a bead of water before, and these were particularly large, so they were easy to observe.

Tip: If you and your children want to take a closer look at water beads, just dribble some water on wax paper. Adding food coloring to the water makes them easier to see.

As my daughter oohed and ahhed over the water beads, my seventh-grader was quick to show off his knowledge by informing her that surface tension made the water form beads. You can imagine that the ensuing conversation between brother and sister left my second-grader pretty confused.

Surface tension is one of those concepts that is simple to experiment and play with at a very young age but remarkably complicated once you start exploring it. Explaining it to a second-grader, long before they know about molecules and forces, is a bit tough. Here's how I explained it to my second-grader: Water is really attracted to itself. So, at the top layer, which we call the surface, it clings together tightly to maximize touching more water instead of the air. When it does this, the layer of water at the surface forms a film that is a little bit elastic — similar to a thin layer of bubble gum.

That simple explanation of surface tension is good enough to let you do and understand a lot of fun explorations. Here's a list of cool activities to try that all have to do with surface tension:

Build a Bathtub Toy Raft Powered by Surface Tension: see how using soap to disrupt the surface tension of water results in enough force to propel a small toy raft.
Make a Milk Rainbow: visualize the movement of water away from soap with food coloring.
Holes That Do Not Leak!: explore how surface tension can be strong enough to plug a small hole and prevent leaks.
Build a Water Strider: experiment to see how the shape of a water strider helps it stay on top of the water's surface.
Blowing the Best Bubbles: discover the best recipe for making bubbles.

My Pick of the Day: Making Water Striders

Since the spill onto the new tablecloth meant we were well into a discussion about surface tension anyway, I figured it was the perfect time to do the Build a Water Strider activity. This activity was on my personal short-list already, as we often see water striders in some of the areas where we kayak, and they're always amazing to watch zip along on top of the water.

As usual, I showed both of my kids the video before we started the activity.

Make a Water Strider - STEM Activity

https://www.youtube.com/watch?v=8h7UZ8pE_Q0

My kids agreed they were up to the challenge of trying to make and float their own water striders. So, we grabbed a spool of beading wire and some wire clippers and got to work. Thinking bigger water striders would be even more fun, the lengths of wire the kids initially cut were about 16 centimeters — roughly twice as long as the instructions called for. I wondered if that would work, or if the total weight would be too much. We forged ahead anyway — after all, science is about experimenting! Twisting the wires together to form the body took a bit of practice, but they both managed it. Then came shaping the legs.

Three photos showing steps of assembling a water strider from wire, cutting, twisting, and bending

Student twisting wire to make a water strider body

About 10 minutes after they started, they were ready to test their first wire water striders. I got out a plate for each kid, and they filled their plates with water and then added a drop of food coloring. The food coloring serves two purposes: it adds to the fun, and it makes it easier to see the water and what is happening.

My daughter went first — immediately her water strider sunk like a brick. She tried three or four more times before declaring it didn't work. I gently reminded her that this was a project that was going to take some tinkering. I encouraged her not to give up and suggested it might be easier to get it working with a smaller water strider.

Student placing wire water strider on the surface of water

So, we cut a new set of shorter (8 cm) wires for her. I also cut a set of wires for myself and did the steps alongside her. It took me a couple of attempts and adjustments to my strider's legs — but I found it fairly easy to make a working water strider, one that could stand on the surface of the water without sinking. What I learned though was that it can be tricky to place the water strider on the water's surface gently enough to not disrupt the surface of the water. Having diagnosed this as a possible point of failure, I offered my daughter my water strider (which I knew was bent properly so that it could stand) so that she could learn, by trial and error, how to set it on the water's surface. It took her a dozen attempts before she got it. She was quite proud of herself once she figured it out though, and that success encouraged her enough to go back to tinkering with the legs of her own strider to try and get it to work.

Meanwhile, my son had quietly been working on his own strider. He, too, struggled to get the longer wires to work and switched to shorter ones. After the switch, he was quick to get a small water strider built and working. A minute or two later my daughter also got her small water strider to work, and both kids had fun looking closely at how the wire water strider stood on the surface and observing how the surface of the water was just slightly bowed under each of the strider's legs. They tried blowing on the water striders to move them across the plate and also experimented with sinking the striders by making waves or rain.

After a few minutes of playing with the working water striders, I was still curious if, having had more practice, we could get the larger water striders to work, too. My second-grader was not interested and wandered off to play, but my seventh-grader was up for the extra challenge. He and I both tried rebuilding the 16 cm striders. It took a bit of trial and error, but after a few attempts, we both succeeded in getting the larger water striders to work. My son's was particularly stable, and he was deservedly proud of himself.

Two wire water striders, large and small, floating in colored water

Overall, this activity was fairly fast, and both kids were very interested in the real world connection to the water striders we see out in nature. The activity basically involves cutting wires, twisting wires to make the body, and then adjusting the legs so that the strider can balance on the surface of the water. It took us less than 20 minutes to get working water striders, and about half of that time was spent tinkering with the legs! While both kids were ultimately successful with the activity, my seventh-grader was much more interested than my second-grader in sticking with it and continuing to explore different designs. He and I easily spent an additional 20 minutes experimenting.

If your kids make water striders, or do any of the other surface tension-related activities, we'd love to see. Post a picture of what they make on social media and tag us. You can find us on Twitter, Facebook, and Instagram.

If this blog post was useful to you, please share it with other parents. Follow the links below to see what other science adventures we've been having at home.

View All Posts in this Series

A science activity log is available as a Word document or as a Google doc for online convenience. (Just choose "File/Make a copy" to save it to your Google Drive.)

About the Author

Sandra, Science Buddies' Vice President of STEM education, holds a PhD in Genetics from Stanford University and has spent the last twelve years working on science education and STEM outreach. Right now, she's stuck working from her home in the Pacific Northwest with her husband, second grader, middle schooler, and two oddly noisy gerbils. She hypothesizes her sanity will hold as long as she gets a daily dose of sunshine.