Cohesion is a property of liquids. Water is very cohesive, it sticks to itself. That’s why drops of water form spheres unless affected by outside forces like gravity or turbulent air.
I like using a cohesion activity when a group of students needs to learn to work in teams. This can lead to a discussion about being a cohesive group.
Sometimes I’m concerned about the class midway through a year and I use a different activity to revisit how to work together.
|Here’s a simple activity you’ll find in my FREEBIE product: Cohesion Pepper.
It’s part of a group of activities that I uploaded to TpT.
I included a presentation with a dozen copyright free images of insects floating on water for you to use to introduce or extend the activity.
Fill a clean container half full of water.
Shake pepper onto the water. Notice that most of the pepper floats on the surface of the water.
Touch a toothpick to dish soap and then touch the toothpick to the center of the water.
You’ll see that the pepper moves away from the toothpick.
The soap weakens the surface tension in the middle of the water. The surface tension around the sides of the bowl is not affected. The surface tension around the sides pulls the pepper to the outside of the container where it sinks to the bottom of the container.
EXTENSION: Touch the outside edges of the water very quickly and you’ll see the pepper moves toward the center of the water. If you’re quick you might form a star.
EXTENSION: This is an easy activity with common materials that can be sent home or shared with families at a science night. To make that easy there’s a small worksheet included in the product, just print, cut in half, and send home.
EXTENSION: Visit the web page created for these products for more information and activities.
Quick Science suggestions take minimal prep time and use common materials.