Freezing Under Pressure Science Experiment

Slippery and Sticky Ice

We have been watching the Winter Olympics, so I decided to do an experiment with ice. It is a simple one, but it ties in well with the Olympic sports.

You will need:

• two ice cubes
• a wash cloth or paper towel

Pick up the two ice cubes. Look for the smoothest side on each cube. This will probably be the top if the cube was made in an ice cube tray, or the side if it came from an ice maker. If you don't like getting your fingers cold, you can use the cloth to hold the ice. Rub the two smooth sides together and you should notice that they slide across each other very easily. It is easy to see why it is so easy to slip on an icy sidewalk.

Next, hold your hand out flat, with your palm upwards. Cover your hand with the cloth and then place the two ice cubes in the center of your palm, with the two flat surfaces touching. Now, squeeze the two cubes together firmly for a few seconds. Release the pressure and examine the ice. They are now stuck together!

How can the ice be slippery one minute and sticky the next? This is something that has interested scientists since the time of my hero, Michael Faraday. In fact, Faraday did quite a bit of experimentation on this very subject. Many scientists claimed that pressure on the ice cubes caused the ice to melt and then when the pressure was released, it would refreeze. Faraday thought that ice always had a thin layer of water on its surface and that when you pressed the ice pieces together, the parts that were firmly in contact were no longer part of the surface. This allowed the layer of water to freeze, connecting the two pieces.

Since then, it has been shown that Faraday was correct. The layer of water gives ice its slippery surface. It can also refreeze if it is between two pieces of ice that are firmly in contact. The thickness of this layer of water depends on the temperature. The colder it is, the thinner the layer. A thinner layer means less "cement," which is why wet snow makes better snow balls than very cold, dry snow. It is one of the reasons the sports announcers talk about how fast the ice is and the quality of the snow.

Don't waste the ice cubes from your experiment. Put them in a glass and cover them with something good to drink. Pop some popcorn and settle back to watch all the science in these sports.

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