Water bubbles orbiting a knitting needle on the ISS

Astronaut Don Pettit is a national treasure. He's been to space three times—once for a six-month stay on the ISS. On every mission, he's found time to make huge contributions to the public communication of science, including making a series of amazing "Science Saturday" videos and inventing (from spare parts he found lying around the ISS) a system to help the space station take clearer, sharper pictures of the Earth at night.

Pettit went to space with an international crew in December 2011 and is currently in space. This new video—where he demonstrates the way a small electric charge can manipulate the behavior of water droplets in microgravity—is a great addition to his oeuvre!

Thanks for Submitterating, James!

Video Link




  1. I had no idea water did that in zero-g. This almost makes sense of accretion discs and all those thing that never made sense about how exactly planets ever get around to forming out of dispersed dust clouds. Apparently god is a knitter.  :)

    1. Water will also sort of do this right here on the surface of the Earth. On a  dry day when you are running your heat a lot, comb your hair with a plastic comb until  you build up a good static charge. turn the sink on to where you have a very thin continuous stream coming out. hold the comb near the water. You will find you can deflect the stream of water.

      This works only because electric charge is unevenly distributed inside the water molecule. Liquids with even charge distribution can’t be deflected.

        1. He mentions charging the water droplets with the nylon knitting needle, so I think this is charge induced in the water, rather than dipole moment. I could be wrong though. My understanding: The nylon needle held next to the syringe pulls charge into the metal of the syringe by induction. The only source of this charge is the water, resulting in an opposite charge on the water when it is ejected from the syringe.

          I think a dipole moment would be more like a tidal force in this case. The net charge in the water would be zero, but imbalanced in the droplet. So the molecules would all orient with the same facing toward the main knitting needle. I’m not sure what the net charge is on the knitting needle, so I can’t tell whether the O atom or the 2H atoms in the water would be the closest to the needle.  OTOH, the comb experiment mentioned above seems to demonstrate that the dipole forces are larger than I expect.

    2. I’m a bit surprised he didn’t mention the biggest difference with gravitational force: the smaller particles orbit the needle at a faster speed than the large ones. For gravitation, orbital velocity at a given distance from the central object is constant because the force is proportional to the mass of the orbiting object, which cancels out when calculating the acceleration. In electrostatics the force is proportional to the charge of the orbiting droplet, and apparently his technique (looks like static induction using the nylon needle) creates a charge on the water droplets that decays more slowly than the mass. (i.e., for smaller masses the charge/mass ratio is higher, not that the charge is necessarily constant)

        1. I remember reading somewhere that they were letting plastic knitting needles on.  Plastic stabby things are ok now but you still can’t bring a bottle of water on.

          1. You can still stab someone with a plastic needle,  and if you have the long ones, with a cord in between, you can do more than stab.  Security measures these days are a joke.  I have a story I wish I could share.

  2. Very cool but I could only watch 2 minutes because the only word that was pronounced with an extreme accent was “knitting.” Yes, I’m a knitting snob…

  3. I’d like to also see the opposite – a container of teflon and like-charged particles being repelled  and bouncing around on the inside.

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