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An Easy Overhead Projector Demonstration of Surface Tension
Discrepant Events Research
LEGO Timeline
LEGO Story
A LEGO Lesson
Evaporation Activity
Condensation Activity
Raindrop Activity
Mass/Weight Misconception
Dissolving Misconception
Living Things Misconception
Air/Oxygen Misconception
Planetary Orbit Misconception
Surface Tension Demonstration
Air Pressure Paradox
Iodine/Starch Paradox
Air Pressure Paradox
Daytime Star Paradox
Mouse Simile
Rabbit Simile
Giraffe Simile
Bear Simile
Air Speed/Flight Demonstration
Cohesion Demonstration
Optical Illusion Demonstration
Lightning Demonstration
Twinkling Star Demonstration
Density Paradox

Science Area:  Chemistry




A dish with water

Liquid Soap





1. Fill a dish with water and place it on the overhead projector.

2. Sprinkle pepper on the water surface.

3. Place a drop of liquid soap in the center of the dish. 

4. Observe the spreading of the pepper. 



You can also use either powdered soap or a bar of soap. 

If you use powdered soap, follow steps 1 & 2, then place a flake or two of the soap in the middle of the dish.

If you use a bar of soap, follow steps 1 & 2, then place a corner of the bar of soap in the middle of the dish.





Why is the pepper floating?


What made the pepper flakes move away once the soap was added?


What is the soap doing to the surface tension of the water?


Would other substances cause this same reaction?



Water is a polar substance.  This means that one end of the molecule is negative and one end is positive.  The positive end of one water molecule is attracted to the negative end of another water molecule.  This causes all of the water molecules at the surface form a film because they are all attracted to one another. This is known as surface tension.  In this demonstration, the pepper is floating upon the film.  When the liquid soap hits the water it disrupts the attraction of the water molecules. The soap has a positive charge to it and the negative poles of the water molecule are now attracted to the soap.  This disruption causes the water molecules to move taking the pepper along for a ride.