· a drinking glass
 · a piece of cheese cloth (or any other thin cloth) large enough to cover the mouth of the glass

1. Fill the glass 3/4 full of water
2. Wet the cloth under the tap (water should be seen to flow easily through the cloth)
3. Place the cloth over the mouth of the glass and push the fringes against the side of the glass.
4. Hold the fringes with one hand against the glass; with the other hand hold the bottom part of the glass without holding the cloth and invert. (Turn it upside down... doing this over a sink might be wise!)
5. Let go of the first hand. The cloth will stay attached and the water will stay in the glass.
 Try This:
  Push a pencil through the cloth on the inverted glass of water without emptying the water from glass?
  The cloth needed to be wet with water so that it could adhere to the sides of the glass (adhesive forces between water and cloth, and water and glass). During the process of inverting, some water poured out, because the cloth is porous, causing an increase in the air pocket volume above the water, which in turn reduced the pressure inside the glass. This activity is also representative of the cohesive forces between water molecules, as a film of water molecules is formed in the little pores of the cloth.
1. Why does the wet cloth cling to the sides of the glass?
2. Explain why some water flows out of the glass in the beginning.
3. Why does the water stop flowing out?
4. What is keeping the water and the cloth up?
5. Can we hold the glass at a slant or sideways without letting the water flow out?
6. What shape does the cloth take when we hold the glass vertically upside down? Why?

Obtaining credit for your efforts

  • Print a copy of the blank laboratory write-up paper.
  • Read and complete each section, incomplete write-ups receive no credit.
  • Have your parent check your work and sign the paper.