Watch drops of water in space 'orbit' a knitting needle like tiny planets

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Ever wonder what planets would look like orbiting a cylindrical sun? Now, thanks to the magic of electric charge, microgravity, and awesome astronaut Don Pettit, you can see for yourself. Watch tiny liquid planets 'orbit' a knitting needle, and find out why they do.

Some days it's hard to recognize that the world is a wondrous place and life is beautiful. Other days, there are experiments like this. Don Pettit, on the International Space Station, is conducting science demonstrations and this one is incredible, giving us a look at orbiting planets in microcosm (although technically the forces at work are somewhat different from those happening with planets). Key to all of this is a lack of significant gravity. Any real downward force would not allow the watery 'planets' to float free around the needle.


First the knitting needle is charged up with paper. The needles is made of teflon, so rubbing it causes it to acquire a negative charge, grabbing electrons from the paper. Meanwhile the water droplets are shot out of a syringe, losing their electrons along the way and acquiring a positive charge. They should splat right into each other, and some do. But some droplets are not heading directly towards the needle. They're flying off to the side, and the pull of the dissimilar charges tugs them off their course. This re-positioning of the droplet subtly change the tug of the needle. Since the water will be drawn toward the center of the needle, as the water glides by the center of the needle the force of the pull will change position relative to it. This alters the course still further, and the water is turned in a circle the way a tetherball is turned in a circle by the force of the string and pole that it's attached to. In this case it's charge that forms the connecting 'string.' In the case of the planets in the solar system, it's gravity. But they both orbit.

The water droplets orbit around a cylinder rather than a sphere, and so their orbits can be a little more adventurous than a planet's orbit. They can get tugged up or down the length of the cylinder by the charge in the rest of the needle, describing a kind of 3D figure eight motion. At last, like our planets eventually will, the droplets fall inwards. But until they do, it's an incredible sight to see the tiny liquid planets in their orbit.


Via Physics Central