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Hi! Can anyone please explain to me why the pepper parts and moves to the sides of the bowl when you touch the water with the tip of the soap? It was such a neat experiment but I couldn't for the life of me explain it to my ds. So embarassed. Is it a fairly obvious answer?

Kimi,

I have no idea! But my husband says it is by a process called diffusion.

When the bar of soap touches the water, the soap molecules begin to dissolve into the water creating outward motion. As a result, the pepper, in this case, is pushed to the sides in an outward motion.
Here is a definition of the process of diffusion:

Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion. The result of diffusion is a gradual mixing of material. In a phase with uniform temperature, absent external net forces acting on the particles, the diffusion process will eventually result in complete mixing or a state of equilibrium.

Hope this helps!

Candice

I think it could also be explained using the concept of surface tension. The water molecules form a "skin" on the top of the water, which the pepper is floating on, but the soap then breaks the surface tension or "skin". If your kids have ever seen water striders before in a creek, those large insects that seem to skate across the surface of the water, you could talk about those and about how they're able to stay on top of the water due to surface tension. A couple related experiments that we've done before that my kids really enjoyed include: Take a bowl and fill it with water. Ask your child if a paper clip will float and then try it. It will sink to the bottom. Then have them carefully lay a piece of napkin or paper towel on the surface of the water, and then lay the paper clip on top of that. As the paper towel absorbs water and gradually sinks to the bottom, the paper clip will stay floating on the water and you can clearly see the "skin" holding it up if you look carefully. It's really cool! Also, take a small bowl of milk and add a couple drops of food coloring in the middle. Swirl it around a tiny bit. Then drop a drop of dish soap in the center and the color will all scoot to the edges of the bowl (very similar to the pepper experiment.)
Hope this helps!
Kristin

Wow! That surely does help. Thanks so much, ladies!!!