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Q: When you fill a glass with water, how can the water rise above the rim of the glass?

The reason this can happen is because molecules of water are strongly attracted to one another. The molecules on the surface of the water are pulled down towards those below them. The attraction of water molecules to each other makes the surface of water act as if it had a thin skin over it. This effect is called surface tension. The force of the attraction is so great that it allows the water to rise a little above the walls of the glass, stretching this “skin” like a rubber balloon.

Try it: In the kitchen sink fill a glass with water. Use a drinking straw to transfer water to the glass drop by drop. Even after the glass looks full to burssting, you can usually add more drops before it over flows.

Special Thanks to CBC 4 Kids: The Lab