Surprise! What happens when you wring a washcloth out in space


Two science students in Nova Scotia posed the question of what would happen if you wrung out a wet washcloth in space. Watch to find out.

When I first clicked play on this video of space station Commander Chris Hadfield wringing out a washcloth in the space station, I thought I knew what would happen. Boy, was I wrong. Take a look and you might be as surprised as I was. But it makes perfect sense.

Water is attracted to itself on a molecular level, creating such wonders as spherical droplets. It’s all because each molecule has a negative and positive side that’s attracted to a neighboring molecule with the opposite charges. Photo: Bob King

Water molecules cling together because of something called surface tension. It’s what makes drops of dew on grass spherical and enables water striders to glide over the surface of a creek as if it were smooth as ice.

You may have noticed it when pouring a glass of water right up to the edge. Try it sometime and look closely; if you’re careful you can fill the glass beyond the rim without water spilling over the side.

Molecules of water are made of two hydrogen atoms attached to either side of an oxygen atom – good old H2O.

Because of the how the electric charges are distributed over the molecule, one its hydrogen “ears” has a slightly negative charge, the other slightly positive.

A water molecule (left). At right, water molecules align according to their electrical attractions to one another. This is how surface tension is created and what made the water form a “tube” around the cloth in the video. Credit: Wikipedia / Qwerter

The positive end attracts the negative end of another water molecule floating by, and the negative end latches onto the positive of another water molecule. When billions of molecules hook up this way they create a loosely-ordered structure or film.

A water strider exploits the surface tension of water to dart rapidly from spot to spot in pursuit of food. Photo: Bob King

Molecules on the surface of liquid water are special. They’re not surrounded by their mates tugging on them equally from all sides. Instead they’re pulled toward one another and downward by molecules water just below the surface.

This makes the water surface contract or “tighten up”, creating a barrier to objects that might penetrate it. Called surface tension, it’s why you can float a paper clip in a glass of water

Careful though. The bonds connecting the molecules are easily broken. Disturb the glass or poke your finger in the water and it will spill or slosh. Had Commander Hadfield wrung the washcloth, water would have broken away from the cloth and flew across the cabin!

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About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

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