Why does a paperclip sink when soap is added

When you added the dishwashing soap, however, you should have observed a change in the behavior of the rubber band and pin: The band should have suddenly popped out into a circle. In addition you should have noticed that adding the dish soap caused the pin to sink to the bottom of the bowl instead of floating. This helps make it an excellent cleaner. After you added the dishwashing liquid to the center of the rubber band the surface tension on the inside of the band broke down.

As a result, the water on the outside of the band still had strong surface tension, which caused it to pull the rubber band outward in all directions.

This made the rubber band pop suddenly into a circle shape. Similarly, after you added the soap to the water you should have seen the pin sink to the bottom of the bowl. Because the soap broke down the surface tension the water could no longer support the weight of the pin. This activity brought to you in partnership with Science Buddies. Already a subscriber? Sign in.

Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. Materials A bowl Water, enough to fill the bowl at least halfway Liquid dish soap A rubber band A metal sewing pin Preparation Fill your bowl at least halfway with water.

Procedure Place your rubber band on a table or other flat surface. Notice its shape when it sits on the table. When you added the detergent, the soap weakened the attraction the water molecules had for each other. This caused the surface film to disappear. Then the paperclip or needle sank. Skip to Main Content. Loading Close. Do Not Show Again Close. Sign In. Sink or Swim Here's an experiment, borrowed from the United States Environmental Protection Agency's website , that helps demonstrate how detergents and other soaps affect our streams.

What you'll need A clean bowl free of detergent Paper clip or sewing needle Fork or tweezers Liquid dish detergent. Adding a drop of liquid detergent provides enough energy to break the surface tension of the water, allowing the paper clip to sink. Summerlin, J. Summerlin, C. Borgford, J. Download a Printable Version. Molecular Structure, Bonding, Orbital Hybridization.