Saturday, 10 January 2015

Science for kids - detergent powered boats

This is an easy one, assuming you occasionally clean your dishes. You just need some bread ties, water and detergent. The video is a little unimpressive, but you could dress the bread ties up to make them look like boats.

Essentially, the detergent is breaking the surface tension of the water, and if you break the surface tension behind the bread tie, the tension in front of the tie pulls it forward. Detergents are surfactants, which means they have a polar end (which is attracted to water) and a non-polar end (which is attracted to oil and grease). This is how detergents (and soaps) bond to both oil and water and hence wash your dishes. Water, without detergent, has a strong surface tension, which is created by the water molecules bonding to each other through Hydrogen bonds. The polar end of the detergent breaks the water surface tension by interfering with the hydrogen bonds at the surface - interestingly, the non-polar ends of the detergent, being hydrophobic, stick up into the air.

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