Toying with Tubing
		Materials: Tygon or vinyl tubing Some oil

Procedure: Pour water in the tube. Notice how the water levels in either side of the tube are always the same regardless of the tube position or diameter. Now plug one side - this is no longer true. Finally, add oil to one side - notice the two levels are different now.

Explanation: The air pressure on both sides initially are atmospheric, so the levels are the same. When one end is plugged, the air pressure in the tube varies with the position of the tube and thumb - hence the different heights. In the last case the oil is less dense than water and therefore the oil level is slightly higher (since the oil is lighter, less water is needed on the other side to balance it).