Following a book of science experiments for children with my daughter, we did the following:
- put some water in a shallow dish;
- put some ground pepper floating on the water surface;
- touch the water surface with the tip of a small stick previously dipped in liquid soap;
- then the floating pepper escapes radially from the soap.
But I was at a loss to explain why. I mumbled something about “surface tension”, but didn't convince even myself.
What was going on?
I am pretty sure that the pepper in itself plays no role but showing the surface motion of water. Am I correct?