The Coolest Preschool Science Activity – Surface Tension

My 4 year old son, R, loves any activity that involves water. So I knew he would enjoy this fun surface tension experiment.

Materials for Preschool Science Surface Tension Experiment

I set up a tray with the following items:

• mat
• empty glass bowl
• jug of water
• ground pepper
• dish washing liquid

Approach to Preschool Science Surface Tension Experiment

R placed the mat and the empty glass bowl on the table. He then poured the jug of water into the bowl. He really enjoyed this process as you can see by the smile on his face. He was very excited to find out what our experiment might be about. R is 4 years old, and this was his first formal exposure to the concept of surface tension so I didn’t want to go into too much detail about molecules and cohesion. I simply explained that the surface of water acts like a stretchy, elastic skin.

After we had discussed the properties of the water’s surface, R poured in the ground pepper.

When I saw how much pepper was in the bowl, I thought we might need more for the experiment to be successful, so R ground some pepper directly into the bowl using our pepper mill. This was a great opportunity to develop some practical life and fine motor skills.

Once we were satisfied that we had sufficient pepper, I asked R to place his finger into the water. “What do you see?” I asked him. “Has anything happened?” He noted that there was no observable change to the water or the pepper.

Next, R dipped his finger into the dish washing liquid.

He dipped his finger into the water again and…..magic! The pepper grounds immediately radiated out to the sides of the bowl. The effect is so fast that it really is exciting to watch. I loved his reaction which was a softly whispered “Wow!” He was so enthralled by it that he repeated the experiment four times in succession.

How it works:

The dish washing liquid breaks the surface tension and as the water molecules try to realign themselves and straighten up again, they gravitate to the sides of the bowl, taking the pepper with them. To explain this in more simple terms for R, I told him that the surface of the water was stretchy and elastic. When a rubber band is snapped, it will bounce off in another direction. So too, when the dish washing liquid breaks the stretchy skin of the water, it breaks and snaps away.

This experiment was quick and simple to put together and R was really fascinated. There are many simple experiments for demonstrating surface tension and we are both excited to try more of them in the future.

Thanks for reading,
Ness