How does a water strider bug walk on the surface of a lake? Why does water bead and roll off of a duck’s back?  Why does water come out of a faucet in large  droplets?  Surface tension, that’s why! In this STEM Lab you’ll be swimming in science as you try to break water’s surface tension and send magical critters sailing away!

 

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Explain It: Students will begin by learning about surface tension and surfactants, and how surfactants affect the behavior of water. Then provide students with a place to float their critters – a sink, a pan full of water, a cookie sheet – any of these will work. You’ll want something that has some distance in though, so make sure you consider that as you find materials. Students will then race their critters across the container of water to test which liquids act as the best surfactant.

Explore it: This is a great activity because it’s open ended for parents/teachers based on the materials you have, time constraints, and ability levels of kids. In our STEM Lab, we’ve included a template of six different 3″ critters that kids can cut out for their experimentation or they can make their own!

All students will need is a critter (or more if they’re doing multiple trials), a hole punch, stop watch, scissors, various surfactants (like rubbing alcohol, vinegar, oil, dish soap, etc), a pan of water, a ruler, and a dropper.

 

1.  Have students carefully cut out the critter of their choice.
2.  Using a hand held hole punch, they’ll punch out a hole in place of the dark circle on their critter.
3.  Using scissors, cut along the dashed lines connected to the punched out hole to create a channel. The channel should be very small but not a slit.
4.  Students will place their critter in the water face side up (because it’s cuter that way!). They should NOT touch the critter again, lest the critter drown.  Students should prepare to time the critter’s travels by grabbing a stopwatch.

READY…
Swimming In Science STEM Lesson
Swimming In Science STEM Lesson
SET…
5.  Without touching the critter, students use a dropper to add a drop of their testing liquid to the punched out hole in the center of the critter.
Swimming In Science STEM Lesson
AAAAANNNNNNNND… GO! Did your critter swim?

6.  Using a stopwatch, have students measure how long in seconds it takes for their critter to come to a complete stop.  Using a ruler they’ll measure how far their critter travels in cm across the “pond”!

Did They Get It? Students run several trials if needed and finish by filling in a data table, graphing their results, and then answering extension questions to check understanding.

 

Here’s a Few Extensions for This Lesson:
  • Have students learn about the chemical composition of each surfactant and why they affect the behavior of water the way they do.
  • Have students try out different weights of paper and record and analyze any new data.

Need to Modify?

  • Pre-cut the critters for students with fine motor skill deficits
  • Lessen/increase the number of trials depending on student levels
  • Review extension questions as a class

Happy teaching!

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