Pepper and Water Surface Tension

Black pepper sprinkled on water races to the edges when a tiny amount of detergent touches the surface. Soap lowers surface tension and the water pulls away from the soap, carrying the floating pepper.

1. Pour 1–2 cm of water into a shallow dish or plate.
2. Scatter a light, even layer of black pepper across the water surface.
3. Gently touch a clean dry finger to the water and note that little changes.
4. Place a tiny drop of dish soap on a fingertip, cotton bud, or toothpick.
5. Lightly touch the soapy tip to the center of the water surface and observe the pepper rush outward.
6. Reapply a trace of soap and touch a new spot if you want to trigger a second motion.

Pepper and Water Science Trick! Surface Tension Mini Segment - learningscienceisfun:

Pepper and Water Science Trick - DaveHax:

📄 Pepper and Soap Experiment - Education.com: https://www.education.com/activity/article/pepper-and-soap-experiment/

📄 A Soapy Magic trick - Discovery Centre: https://discoverycentre.thekids.org.au/siteassets/pdfs/germs/2---activity-at-home---a-soapy-magic-trick.pdf

• Test different soaps or detergents and compare how strongly they move the pepper.
• Try warm versus cold water to see how temperature affects the speed of motion.
• Swap pepper for ground cinnamon or paprika to compare particle size and hydrophobicity.
• Float a small paper raft, then touch soap behind it to make a simple surface tension boat.

• Do not put anything from the experiment into your mouth.

*Why does the pepper float instead of sinking or dissolving?

• What property of soap changes the behavior of the water surface?
• Why does the motion stop after a short time even if pepper remains on top?
• How would using skim milk, whole milk, or salt water change the result, and why?