How to turn a leaf into a boat
Turning a leaf into a boat using liquid soap
- cotton swab;
- liquid soap;
- glass dish;
Apply some liquid soap to the tip of the leaf with a cotton swab. Toss the leaf into a dish filled with water. Note that it sails like a boat!
At the border between the boat and the water’s surface, the water is actively “pulling” the boat to itself. This force “pulls” the boat in all directions equally, and therefore the boat remains stationary. This force directly depends on surface tension. Soap contains surfactants, which reduce the surface tension of the water. This weakens the soapy water’s “grip” on the boat significantly. It would seem that soap pushes the boat forward; in fact, the opposite is true! The undiluted water pulls the boat harder than the soapy water, drawing the boat away from the soap film.