Surface Tension - Thread On Water

Purpose

To demonstrate how detergent decreases the surface tension of water.

Equipment

Glass dish with water, liquid dishwashing detergent, thread loop, overhead projector.

Suggestions

Keep the thread near the center of the dish; use only a small drop of soap solution.

Setup Time

5 min.

Images

f3-04

Description

Fill a container with water and place it on the overhead projector. Place a loop of thread on top of the water such that it forms an irregular shape. A drop of detergent solution gently placed inside the loop with the eyedropper reduces the surface tension of the water inside the loop. The greater surface tension outside the loop then pulls the thread outward into a uniform circle.

References

Ernest K. Chapin, Surface Tension and Floating Bodies, AJP 24, 178 (1956). ◙Ernest K. Chapin, The Strange World of Surface Film, TPT 4, 271-275, 286 (1966). ◙Richard Marble, Floating Objects, TPT 10, 67-68, (1972). ◙James T. Schreiber, Barroom Physics, Part II, TPT 13, 418-428, (1975).