Here's a quick and simple science experiment you can do with basic things in your kitchen!
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).
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
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!