Bending Water with a Plastic Comb

SmarterThanThat Experiments

Sunday, 30 November 2008 01:47 Written by mooeypoo

Yes, yes, I seem to have an affinity towards bending stuff, specifically wet stuff. Last time I bent a laser beam using water, and this time I’m going to magically bend water using a plastic comb.

Science magic! Okay, well, it’s not quite magic, it’s science magic, which means it has (as always) a perfectly good explanation to it. But - can you guess it?

This is a very straight forward demonstration about static electricity, and it is working so well, that it really is fun to do anywhere with a faucet (and a plastic comb..).

What Do You Need?

• A plastic comb or a nylon balloon.
• Dry hair.
• Dry environment (humidity is baaaad)
• A very thin flow of water (about 1 cm thick, or for all you metric-deniers, about 1/16th of an inch).

What’s Going On?

Well, the plastic comb is made of molecules (as is every other matter) that have electrons floating around them. Electrons have a negative charge, and just like a polarized magnet, they are repelled by other negative charges.

When I comb my (dry!) hair with the plastic comb, it collects electrons from the individual strands of hair to itself. About 10 strokes should be enough to make the charge strong enough for the demonstration. The electrons move from my hair strands to the comb and, therefore, lose negative charge. The individual hairs become positive (because they have lost negative charge), the comb becomes negative (because it gained negative charges, in the form of electrons).

The molecules in the water stream are neutral - they have both positive and negative charges, and all their electrons nicely floating around wherever they are supposed to be. When I move the (now negatively charged) comb next to the water stream, the electrons that are closer to the comb are being repelled away. The molecules that are closer to the comb, therefore, become positive, and away from the comb there is more negative charge (more electrons).

The side of the water flow that is closer to the comb is now positively charged, and the comb is negatively charged. Positive and Negative attract one another, and that concept allows the water flow to bend towards the comb.

Voila! instant science magic!

Practical Applications

Static electricity exists in nature, as you may well have noticed in a hot, dry day, trying to open a metal door knob and heard a tiny Bzzzz, followed by an inconvenient sting. Our body exchanges electrons with the surroundings all the time, gathering up and discharging static electricity. But there are more applications and phenomena that are attributed to static electricity:

• Electrostatic Percipitator: This invention is used to clean the air from other particles by inducing electrostatic charge. It’s quite useful, specifically for power plants or big industrial facilities.
• Xerography: this is a photocopying technique developed in the late 1930s. It distributes a uniform electrostatic charge on a surface of a drum. The image is then lit through (so wherever there is color, the surface remains unlit) on a grid on top of the charged drum. The light dissipates the charge, so the grid remains charged only where the image is printed. Then, carrier particles are mixed through the drum and “soaked” into the paper - so they “stick” where the charge exists, and therefore duplicate the image.

More References

• This demonstration on about.com: http://chemistry.about.com/od/chemistryexperiments/ht/bendwater.htm
• This demonstration on sciencebob.com http://www.sciencebob.com/experiments/bendwater.html
• This demonstration on SciFun@Wisconsin university: http://scifun.chem.wisc.edu/homeexpts/BENDWATER.html
• This demonstration on Science Made Fun: http://www.sciencemadesimple.co.uk/page30g.html
• Wikipedia entry on Static Electricity: http://en.wikipedia.org/wiki/Static_electricity

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