Rotating Ice Experiment

Materials

ice cubes
a bowl
warm water
food coloring

Procedure

Fill the bowl with warm water. Place an ice cube into the water. Now watch it as it melts. Don't get bored and give up yet. Watch for a minute and something should happen. The ice cube will tip over on its side. A short while later, it will turn again, and then again. It will keep turning over every minute or so until there is no ice left. Why did it turn over?

Conclusion

The warm water was melting the ice that was under the surface, but the top of the ice cube melted more slowly. This caused the ice cube to get top-heavy. It became unstable and tipped over. Then the same thing happened again and again.

Using half red/half plain Ice Cubes

It may be difficult to tell whether the ice cube was turning over or just rocking a bit. To make it easier, some special ice cubes may be used.

Put a few drops of red food coloring into some water and then fill the ice cube tray half-full with the red water. Put that in the freezer and let it freeze solid. Then add some very cold, plain water. The plain water must be very cold to start with (you may stirr it with some ice) to keep it from melting the red ice. Quickly putting this back into the freezer, to get the half-red and half clear ice cubes.

Make some red and clear ice cubes and try the experiment again. It is much easier to see when the ice cube tips, but you will also see other interesting things. The red ice melts, and you get streamers of red water flowing downwards from the ice cube. Though the ice is less dense than the water (which causes it to float), the very cold water of the newly melted ice is more dense than the surrounding water, so it sinks. It is not the coloring that makes it denser. You can see this even without the food coloring, but the color makes it much easier to see. Very cold water sinks, but when it gets even colder, it suddenly expands, rises and freezes into ice which floats. This is just one of the many things that make water one of the strangest chemicals we know of.