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Scared Pepper

Cohesion is the word for this strange force.


- pepper,
- cup,
- water,
- dish soap.


We all know how glue or tape can be used to stick two objects together. Cohesion occurs on common everyday objects, for example rain to a car's windows or chewing gum on your clothes.

1. Fill a dish with water.
2. Sprinkle some pepper on top of the water.

3. Drop several drops of dishwashing detergent in the center of the water.

What happens to the pepper?



The pepper stays scattered all about the water. Water is pulling on the pepper evenly from all directions. When you drop the detergent into the water, it reduces the cohesiveness between the water and the pepper. ( It reduces the pulling action on the pepper and the pepper appears to run away from the detergent).

Cohesion is the force that holds a material together. It results from the attraction that atoms and molecules have for one another. This attraction decreases as the distance between particles increases. Thus, with few exceptions, cohesion is highest in solids. Liquids are less cohesive than solids, and gases are practically noncohesive.