Surface Tension Racers

They zoom on molecular power.

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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 - 

· Photocopy the template onto card about 220 ppt (about the weight of manila folder card)

· cut out one of the boat shapes, taking care to cut out the inner hole as well.

· Half fill the trough with water and gently float the boat at one end facing into the middle.

· 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.