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Check out this video of a cool experiment conducted by astronauts and then stick around for the science.

The Science

Water is Partially Charged

What is happening here, as was explained by the astronaut in the video, is the interaction of electrical charges. When you rub a surface like polystyrene (the material of the knitting needles) or PVC (polyvinyl chloride) with a piece of cloth (silk usually works the best), electrons are transferred from the cloth to the surface of the needle. Since electrons are negatively charged, this transfer gives the surface of the needle a negative charge.

So how does this negatively charged needle interact with water? As a whole, a molecule of water does not have an overall positive or negative charge. However, water is what is called a polar molecule. This means that one end of the molecule is slightly positive and the other is slightly negative.

Oxygen is a very "electronegative" element. In the water molecule, although it shares electrons in a covalent bond, it hogs the electrons so that they are closer to the oxygen than they are to the hydrogen. This results in the hydrogen parts of the water molecule being slightly positive and the oxygen end being slightly negative (because electrons are negatively charged, having less of the share of them will result in a positive partial charge).

The charges average out as a whole molecule, but this polarity allows water to interact in interesting ways. For example, the reason why water is such a good solvent, or good at cleaning up dirt and dust, is because its partial charges interact with the particles and allow them to be washed away. Additionally, the reason why water has a surface tension and forms droplets (cohesion) is because of these partial polar charges interacting with other water molecules.

Charges can Interact Forcefully

So the reason that the knitting needle and the water droplets interact is because the needle has a negatively charged surface and the water droplets have a slight positive charge. These opposite charges attract.

According to the physical principle Coulomb’s Law, charges at a distance exert a force on each other. Opposite charges exert a force to attract each other and similar charges exert a repelling force on each other.

All of this means that once the water droplets in the video are set in motion, they are forcefully attracted to the needle, and because of the lack of any gravitational force, they go into “orbit.” The kinetic energy from the droplets moving through space and the electric attraction from the needle interact in such a way to produce the phenomena in the video above. Of course, trajectories, amount of charge, droplet velocity, etc., all play into this interaction, but the resulting video is fascinating enough to stick around for the fascinating science.


SIDE EXPERIMENT: You can test the attractive properties as seen in this video in your own home (sadly without the orbiting). All you need is a balloon and a faucet. Blow up the balloon and rub it on your head to create a charged surface on the balloon. Start the faucet and then slowly move the balloon closer to the stream of water. Amazingly, you will see the flow of water contort to the balloon!

Remember that this is because of the negatively charged surface of the balloon interacting with the partially positive charges of the water. Science!