Science project

Soapy Surface Tension

Research Question:

How does soap affect the surface tension of water?

Did you know that the molecules on the surface of a cup of water stick together? This is because of a force called surface tension. In fact, if you carefully place a paper clip on the surface of a cup of water, it will seem to float because of surface tension. But what happens when a drop of soap hits the water’s skin? Find out with this science project.


  • Pennies
  • Plastic Cup
  • Water
  • Eye dropper
  • Liquid soap

Experimental Procedure:

  1. Fill a plastic cup with water.
  2. Dip the dropper into the cup, and suction in some water.
  3. Place drops of water from the dropper onto a penny, counting how many it takes for the water to spill off the penny. This is the number of drops it takes until the surface tension breaks.
  4. Dry off the penny.
  5. Repeat this process several times to make sure that you have an accurate count of how many drops it takes to break the surface tension.
  6. Dilute the water in the cup with a drop or two of liquid soap.
  7. Now see how many drops of water it takes until the water spills off the penny. How can you explain the difference?

Terms/Concepts: Surface tension; Water skidder (insect); How does soap interact with water?


  • Experiments With Bubbles, by Robert Gardner. Pp 18-20.
Disclaimer and Safety Precautions provides the Science Fair Project Ideas for informational purposes only. does not make any guarantee or representation regarding the Science Fair Project Ideas and is not responsible or liable for any loss or damage, directly or indirectly, caused by your use of such information. By accessing the Science Fair Project Ideas, you waive and renounce any claims against that arise thereof. In addition, your access to's website and Science Fair Project Ideas is covered by's Privacy Policy and site Terms of Use, which include limitations on's liability.

Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state's handbook of Science Safety.

Add to collection

Create new collection

Create new collection

New Collection


New Collection>

0 items