Why does pepper move away from soap?
Touch the water with a clean stick, then a soapy one
Surface holds together
Tiny particles of water attract each other. On the surface, they seem to hold on to their neighbors, and an elastic boundary is obtained.
This is called surface tension. Thanks to it, light dry grains of pepper can remain on the surface.
Touch the water with a clean stick. There will be a small ripple, but the pepper will not scatter to all edges.
Soap releases tension
A drop of soap got into the middle. At this point, the soap particles prevent the surface of the water from sticking together as strongly.
Near the edges the tension is still stronger. It pulls the surface from the soapy place outward - the water begins to move.
Floating peppercorns leave with the water. They are not afraid of anything: they are carried by the flow.
The place of the drop changes its movement
Let's start again with fresh water. Now let's add soap not in the middle, but near the left edge.
There the tension will become weaker. The surface will stretch from this place to the side where the tension is even stronger.
The pepper will move with the water again, but the movement pattern will be different. We only changed the place of the drop.
For adults · discuss together
The peppercorns are enlarged. After each run, we take fresh water so that the results can be compared.
Before experience
Ask: “What do you think will happen?” Let the child check his guess first.
After the experience
What has changed? What remains the same? Where can you notice a similar phenomenon?
