A simple and amazing experiment to entertain your child
Reagents and equipment
- freshly-ground pepper;
- cotton swab;
- liquid soap.
Fill the plate with water and grind some black pepper into it; the pepper should float on the surface. Apply some liquid soap to one end of a cotton swab, then dip the soapy swab in the water. Observe as the pepper “escapes” to the edge of the plate. To repeat this experiment, rinse the plate thoroughly and refill with fresh, non-soapy water.
Water’s strong surface tension suspends the ground pepper particles on the water’s surface. The surfactants contained in soap reduce this same surface tension. The water pulls the pepper away from the spreading soap film because the force of attraction between water and pepper is greater than that between soap and pepper.