Pepper & Soap Experiment

Use this experiment to show your kids the strength of soap! Pepper floats on the surface of water due to surface tension. That means the molecules on the surface of the water hold onto each other so tightly that they create a strong layer that keeps the pepper afloat. But when soap is dropped into the water, it breaks the surface tension and the pepper pieces shoot away.

  1. Ages: 5 - 8

  2. <30 minutes

  3. A little messy


Step-by-step tutorial

  • Step 1

    Shake or grind the pepper to cover the surface of the water.

    Photo reference of how to complete step 1

  • Step 2

    Ask your child what they expect will happen when you drop the soap in and why. What do other things do when you drop them into water? Then drip a drop of soap into the middle of the bowl (or put soap on your finger and touch the middle).

    Photo reference of how to complete step 2

  • Done!

    The pepper swims away!
    Did the pepper do something different than what your child expected? How interesting that adding soap to water can make it do something that you didn't expect! Water has a surface that allows light-weight things to float on it. This is how water bugs walk on water. But soap breaks this surface tension, so when the water's "skin" scoots away from where it was popped, the pepper goes with it!

    Photo reference of how to complete step 3

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