Surface Tension Racers

that zoom on molecular power.

 

 

 

Category - Solids, Liquids & Gases

Key Idea - Surface Tension

 

Purpose - Demonstrates the effect of detergent on the surface tension of a liquid.
Nature -  Demonstration  or Class Practical
Materials -  a copy of the template (available by clicking here), card, a shallow trough, water, detergent in a dropper bottle.
Method - 
  1. Photocopy the template onto card about 220 ppt (about the weight of manila folder card)
  2. cut out one of the boat shapes, taking care to cut out the inner hole as well.
  3. Half fill the trough with water and gently float the boat at one end facing into the middle.
  4. Drop a small drop of detergent into the hole at the centre of the boat and watch the boat zip across the trough. 
Safety - Nil
Explanation - Detergent is a substance that breaks the bonds between water molecules.  Because of the surrounding boat, the surface tension recoil only goes in one direction, forcing the boat along. 
Notes - The fact that detergent breaks surface tension is exactly what makes it useful in cleaning.