Let us make water appear to boil with only the touch from a finger.
Things Required:
Cotton handkerchief
Clear drinking glass (with straight, smooth sides)
Rubber band
Directions:
Wet the handkerchief with water. Squeeze out any excess water. Fill the glass to the top with water. Drape the wet cloth over the mouth of the glass. Place the rubber band over the cloth in the middle of the glass to hold the cloth close to the glass. Use your fingers to touch the cloth down about one inch below the water level.
Pick the glass up, hold the bottom with one hand, and turn it upside down. Note: There will be some spillage, so do this over a sink. Place the other hand under the hanging cloth and hold the glass. At this point one hand is holding the cloth next to the glass with the free end of the cloth draped over this hand. With the free hand push down on the bottom of the glass. Allow the glass to slip down slowly into the cloth.
This Is What Happens:
The water does not fall out of the glass and it appears to start boiling.
Science Behind It:
Water does not flow out of the cloth because the tiny holes in the cloth are filled with water. Water molecules have a strong attraction for one another which draws them close together. This causes the water to behave as if a thin skin were covering each hole in the cloth, preventing the water in the glass from falling out.
Pushing the glass down causes the cloth to be pulled out of the glass. This outward movement of the cloth creates a vacuum inside and the air outside is pushed through the cloth. Small bubbles of air form inside the water, giving an appearance of boiling water.
